Journal of the Institute of Petroleum, Vol. 31, No. 262

Vol. 31. No. 262. O c t o b e r 1945.

CODE OF ELECTRICAL PRACTICE FOR THE PETROLEUM INDUSTRY.

Al a n D. Ma c l e a n ( F e llo w ) . Pr e f a c e.

I h a v e been requested to present this pap er in m y capacity o f Chairm an

and spokesm an of th e Sub-Com m ittee of th e In s titu te of Petroleum appointed to d ra ft th e Code of P ractice form ing its subject.

I would like, a t th e outset, to p a y a sincere trib u te to m y fellow-members on th e com m ittee an d others associated w ith th e w ork for th e enthusiastic a tte n tio n th e y hav e devoted to th e production of th e Code. I t has not been easy for an y of th em to spare th e tim e an d trouble th e y have so willingly given to see it through.

We are all alive to th e im perfections of th e result, b u t feel th a t a fair sta rt has been m ade to fill an im p o rtan t need, and th a t if th e Code is k ep t under regular revision as experience is gained in its application a n d to keep it abreast of electro-technical developm ent, it will be of considerable a n d lasting service to th e petroleum industry.

I t is n o t easy to m ake a paper of this k in d interesting, or indeed very informative, to any who have n o t read th e d ra ft Code itself. All I can do in a short space is to give some account of th e w ork of th e drafting com­

mittee and indicate th e form an d scope of th e Code a n d some of its more im portant basic aspects.

The Code was compiled w ith th e idea of its being issued by th e I n s titu te of Petroleum as a guide to appropriate electrical practice applied solely to the petroleum industry. Some p a rts of it are still under consideration by various com m ittees of th e In stitu te , an d it has recently been suggested by th e B.S.I. th a t w hen it has reached final form it m ight instead be issued by th em as a B.S. Code of P ractice.

N either this paper n o r th e Code itself p u rp o rts to em body or disclose any original work, b u t m erely to survey a n d correlate th e w ork an d views of other workers in th is field a n d to ex tra c t an d set o u t reasonable and practical rules for th e guidance of those concerned w ith electrical m atters in th e industry.

Certain controversial m a tte rs th a t have emerged during drafting will be m entioned in th e hope th a t these m ay draw suggestions for im provem ent.

Or i g i n s o f t h e Co d e.

As m ight be expected by those of us who knew of his pioneering work in th e application of electrical power to all purposes in th e petroleum industry, and th e continuing in te rest th a t he took during his lifetime in all m a tte rs electrical, th e idea of compiling a B ritish Code of Electrical Practice relate d specifically to th e problem s an d conditions encountered in th a t in d u stry , originated in th e m ind of t h e j a t e . President of th e In stitu te , Mr. C hristopher Dailey.

E E

H e, like others of us concerned in th is work, h a d become increasingly conscious of th e growing need for th e developm ent of sta n d a rd lines of electrical equipm ent especially suited to these conditions. Also, as refinery processes an d products becam e m ore diverse, th e v a rie ty of kinds and sources of risk increased, so th a t one h ad a t tim es to look to th e practice followed in other industries to find guidance for certain applications in our in d u stry , a n d he felt th a t a com pilation giving fairly general guidance on th e selection of suitable electrical equipm ent an d m ethods of installation would be helpful.

In addition, it was felt t h a t such a Code would assist B ritish m anufacturers in m eeting th e needs of th e in d u stry overseas as well as a t home.

D uring 1941 some a tte n tio n h a d been directed to th e m a tte r by the P etroleum D ivision of th e M inistry of F u el a n d Pow er in connection with proposals form ulated b y them for th e pro tectio n of oil storages under war­

tim e conditions. These proposals included certain recom m endations relating to th e use or incidence of electricity, including lightning an d static.

In 1942 a G overnm ent P etroleum In sta lla tio n s C om m ittee was set up b y th e M inistry of F uel an d Power, a n d form ulated, as p a r t o f a special report, rules for th e use of electricity in buried in stallatio n s for spirit storage. These rules were subsequently ad o p te d b y th e P etroleum Board an d th e G overnm ent D ep artm en ts concerned, a n d are a t present in operation.

R equests were a t th is tim e received b y th e I n s titu te from G reat Britain a n d overseas for guidance in reg ard to these m atters, and th is intensified Mr. D ailey’s feeling th a t, although n o t easy to achieve in w ar-tim e, a code o f practice generally rep resen tativ e of th e views of th e in d u stry itself should if possible be produced.

Discussions in th e I n s titu te an d th e in d u stry generally m ade it apparent th a t, p articu larly in regard to oilfields, where conditions v a ry enormously, and to a lesser e x te n t in refineries a n d installations overseas, a considerable diversity of opinion a n d practice prevailed.

In th e absence of a u th o rita tiv e guidance, an d indeed in some cases of suitable p la n t an d equipm ent available from B ritain, some B ritish concerns h ad necessarily adopted A m erican p la n t a n d practice or developed their own.

Moreover, a p a rt from th e obvious desire of all concerned to follow safe, sound an d reasonably uniform practice, th ere appeared to be some danger th a t unless th e in d u stry itself produced some guidance, unnecessarily onerous or unsuitable a n d ham pering regulations m ight be im posed upon it from w ith o u t through im perfect knowledge of th e n a tu re and e x te n t of th e risks involved on th e p a rt of those fram ing th e regulations.

Co m m i t t e e o f El e c t r i c a l a n d Al l i e d Ma t t e r s.

The first step ta k e n by th e In s titu te was th e form ation in Ja n u a ry , 1943, of a com m ittee know n as th e Com m ittee of E lectrical a n d Allied M atters, under th e C hairm anship o f Mr. Dailey, to explore th e m a tte r.

This Com m ittee was generally rep resen tativ e of th e m ajo r B ritish oil com panies operating in B ritain an d overseas. I ts term s of reference were to collate a n d review existing au th o rita tiv e rules for p a rtic u la r conditions 380 MACLEAN : CODE OF ELEC TR IC A L JTKAUTKJE

FO R TH E PETR O LEU M IN D U STR Y . 381 a n d to o btain particulars of th e rules a n d practice followed by th e m ajor companies, which together w ould form a basis for regulations to be issued by th e I n s titu te of Petroleum . In addition to dealing w ith electric power and lighting, guidance was to be given in regard to protection against lightning an d static electricity.

Dr a f t i n g Su b-Co m m i t t e e.

A fter arranging to obtain for consideration particulars of th e electrical practice followed b y th e m ajor companies, a sub-com m ittee composed of electrical engineers connected w ith these companies was formed, w ith m yself as Chairm an.

Our term s of reference were very wide, comprising consideration of the above-m entioned applications of electricity and incidence of electrical phenom ena th ro u g h o u t th e in d u stry —as Mr. D ailey p u t it, “ from th e oil well to th e kerbside p u m p .”

I t soon becam e ap p aren t th a t certain premises for which special provision is already m ade in G overnm ent or Local G overnm ent regulations, such as tankers and public garages, should for th e tim e being be excluded from th e purview of th e Code.

I t was also recognized th a t special consideration m ay la ter require to be given to th e requirem ents of such processes as can repairing w ith electrically h eated soldering irons.

I t m ay be m entioned th a t since th e D rafting Com m ittee began its work the whole question of th e use of electricity in so-called dangerous industries has received, and is still receiving, widespread a tte n tio n . A notable paper has been read before th e I.E .E . upon “ In d u stria l Eire Risks ” by W.

Fordham Cooper an d F. H . M ann, which touches upon th e risks encountered in th e petroleum industry, am ong others. Several articles dealing w ith th e design an d installation of flam eproof an d intrinsically safe ap p aratu s have appeared in th e technical press.

An extrem ely valuable an d comprehensive Review of Electrical Research and Testing w ith regard to F .L .P . enclosure an d In trin sic Safety of Electrical A pparatus a n d Circuits has been issued by th e M inistry of Fuel an d Power w hich goes a long w ay in clarifying ideas ab o u t th e problem s involved in these m atters an d th e technical factors entering into their solution. The review m akes it clear th a t a good deal of fu rth er research is needed, especially in regard to intrinsically safe ap p aratu s and circuits, before com plete solution of th e m ap y problem s is achieved, b u t a t least th e n a tu re of these can now be seen w ith considerable clarity, an d th e lim itations of solutions offered so far can be largely defined w ith safety.

A com m ittee of th e I.E .E . is a t present engaged upon drawing up a section of rules for th e installation an d m aintenance of flameproof apparatus.

Com m ittees of th e B .S.I. are engaged in revising th e B.S. Specifications for F .L .P . an d for intrinsically safe ap p aratu s and circuits. The revised Specification No. 229 for F .L .P . ap p a ratu s in p articular is of especial im portance to th e petroleum industry, as it will classify types and require­

m ents of such a p p a ratu s over a wider range an d in m uch greater detail th a n h ith erto .

The In s titu te of Petroleum is represented on these committees, and to

382 MACLEAN : C O D E O F i / L U J A X V 1 U A L i I DA L i l C i i

some e x te n t th e needs of th e in d u stry will be m e t b y th is co-operation, h u t th e full ground is n o t covered b y th is outside w ork, a n d it is still felt t h a t a com prehensive Code specifically and solely concerned w ith ou r aspects of th e problem , a n d rep re sen tativ e of th e views of B ritish oil in tere sts, is desirable.

I n th is connection it m ay be m entioned th a t th e D raftin g Sub-Com m ittee is com posed of electrical engineers, all o f whom have h a d a num b er of years experience in th e oil in d u stry which, ta k e n together, covers oilfield, refinery, a n d d istrib u tio n practice. I t is a com m ittee of users, n o t m anufacturers or civil serv an ts. T hey are n o t so m uch concerned w ith design as w ith th e requirem ents of design. T hey are, however, not chem ists, drillers, producers, or refiners, so t h a t in assessing risks th e y have necessarily had recourse to advice based u p o n th e experience of th e ir chem ical a n d other specialist colleagues.

The a ttitu d e of th e electrical com m ittee has been, in effect, to say to th e ir colleagues, “ Y ou tell us th e n a tu re a n d properties of a given atm o­

sphere an d we shall tell you w hether or n o t it is safe to use electrical a p p a ra tu s hi it a t all a n d if so w h a t ty p e of available a p p a ra tu s to employ a n d how to in sta l a n d use i t . ”

A nother p o m t to bear in m ind is t h a t th e Code is concerned prim arily w ith avoidance o f ignition of inflam m able atm ospheres by electric arcs or sparks, an d not of danger to life from shock or to x icity . This la st point is of im portance, as in th e m a jo rity of cases in th e oil in d u stry avoidance of toxic concentrations will au to m atically exclude risk of explosion.

C ustom ary precautions ta k e n in th is connection, therefore, render the in d u stry safer from electricity risks th a n m ight a p p ear a t first sight.

Fo r m o f Co d e.

The Code is divided in to four m ain Sections, n am ely :—

Section I .—Introduction describing th e scope a n d purpose of the Code.

Section I I . — Definitions o f th e term s requiring to have a specific m eaning a tta c h e d to th em to m ake th e in te n t a n d application of the R ules clear a n d unam biguous.

Section I I I .— E x p lan ato ry Schedules to describe th e purpose and basis of th e Rules.

Section IV .— The Rules them selves.

Section I .— Recom m endations covering certain suggested pre­

cautions n o t given m a n d ato ry statu s.

W ith th e exception of th e In tro d u c tio n a n d th e R ecom m endations, each o f th e above sections is sub-divided u n d e r various headings to facilitate reference to p articu la r applications.

The m ethod followed in compiling th e Code has been to refer a n jT p articu ­ la r subject requiring special stu d y for its clarification to one m em ber of th e C om m ittee, who has produced for general discussion a d ra ft Schedule, a section o f D efinitions a n d a set of R ules dealing w ith it.

A general review was first m ade o f A m erican codes of rules a n d explosion- p ro o f ap p ara tu s, B ritish coal-m ining practice, a n d F .L .P . ap p a ra tu s, also

FO R T H E PETR O LEU M IN D U STR Y . 383 of B ritish rules, such as those contained in th e Petroleum (Consolidation) A ct, those issued by the R ailw ay Clearing House, th e Home Office, th e M inistry of L abour an d N ational Service, and th e In d ian and Canadian G overnm ents, as well as th e statem en ts of practice followed by th e m ajor oil companies an d th e rules recently form ulated by G overnm ent committees.

This review indicated th a t to ex tra c t th e essential inform ation from these and p u t th is into a form capable of general application and acceptance would require som ething m ore th a n th e production of a bald set of rules w ithout explanation.

In view p articu larly of differences in term inology ra th e r th a n in ten t, it was found desirable to a tte m p t to define clearly n o t m erely th e electrical term s employed, b u t o th er term s used in th e in d u stry an d th e conditions of risk likely to be encountered.

I t m ay be suggested th a t to define or assess th e n a tu re of w hat m ay be described as th e petroleum or chemical factor of th e risk is n o t w ithin the province of th e electrical engineer, b u t before he can recom m end suitable electrical p la n t an d precautions he m ust know som ething of th e physical and chemical n a tu re of th e atm osphere in which it is to operate. This has been recognized by th e o th er Com m ittees referred to previously who are dealing w ith certain aspects of th e problem . F .L .P . p lan t, for instance, is classified by th e perm issible gap betw een flange faces, which depends on th e n a tu re of th e atm osphere which is likely to surround it, so th a t a classification of such atm ospheres is necessarily included in its specification.

I t is n o t custom ary, in codes of practice, to include m uch in th e w ay of explanatory m atter, b u t in th e present case it was considered desirable to describe ra th e r more fully th a n usual th e n a tu re of th e problem s dealt w ith and th e principles underlying th e com paratively brief rifles an d recom ­ m endations finally arrived at. One reason for th is was th a t it would help officials a n d engineers in th e field, especially overseas, who could n o t readily obtain advice or explanation, to in terp re t th e in te n t of th e Code and apply it to unusual cases.

The following brief com m ents on each section of th e Code will bring out th e m ain points in each which m ay give rise to useful discussion :—

Section I . —Introduction.

This explains th a t th e Code does n o t p u rp o rt to indicate w hat constitutes safe an d reliable electrical practice in general, b u t is intended rath er to supplem ent existing regulations in this respect w ith guidance in regard to th e application of special electrical practice a n d a p p aratu s to th e particular conditions encountered in th e petroleum in d u stry w ith a view to the avoidance of fire or explosion.

Reference is m ade to th e sim ilarity th a t exists to some ex te n t between th e petroleum an d coal-mining industries, b u t it is pointed out th a t on the whole conditions in th e oil in d u stry are considered to be less hazardous th a n in coal m ining.

Section I I . —Definitions.

The objects aim ed a t in fram ing definitions of term s used in th e Code were :—

384 MACLEAN : CODE OF E L E C TE IC A L PR A C TICE

(a) To secure some m easure of b re v ity in th e rules them selves w ith o u t introducing am biguity.

(b) To identify, b y m eans of consistent term s, conceptions th a t are given different and often am biguous or unacceptable nam es in several different codes.

(c) To define certain conditions, classes of risk, etc., w hich seemed to call for e x act definition, a n d for w hich no very clear definitions appeared to exist in o th er publications.

As originally d ra fted th e definitions were fairly num erous, an d some of th e m were ra th e r clumsy, b u t, w ith th e assistance of a special P an el of the N om enclature C om m ittee, th e y have been g reatly reduced in num ber and im proved in clarity of expression. Term s which m ay be ta k e n as commonly understood have been excluded, a n d only those ab o u t which am biguity m ight lead to a m isin terp retatio n of th e in te n t an d application of th e Code have been retained.

P a rtic u la r in terest n a tu ra lly attach es to th e definitions of dangerous atm osphere, d angerous location, an d dangerous area.

I t was a t first hoped t h a t all conditions encountered m ight be classed as either safe or dangerous, th e la tte r class being em braced w ith in th e above definitions, b u t it was la te r decided t h a t in reg ard to oilfields it seemed essential to introduce an interm ediate class described as remotely dangerous.

I t m ay be m entioned t h a t th e necessity for som ething of th is kind has been recognized by o th er authorities.

T he argum ents on th is question will be in d icated in th e rem arks made ab o u t th e corresponding ex p lan a to ry schedules.

F o r th e present it is sufficient to sta te t h a t th e som ew hat arbitrary distance of 50 feet from a dangerous location or a possible p o in t of emission of a dangerous atm osphere, which is ta k e n as defining a dangerous area or space, accords w ith th e definition laid dow n in th e rules of th e Petroleum In stallatio n s C om m ittee of th e M inistry of F u el an d Pow er referred to previously.

I n regard to electrical definitions, those given in th e G lossary of Terms num bered B.S.S. 205 have been ad o p ted so fa r as th e y apply. Definitions are given of additional electrical term s used in th e Code, e.g., “ non-spark­

ing ” ap p a ra tu s suitable for use, w ith ad eq u ate precautions, in remotely dangerous areas in oilfields.

The definition of flam eproof dem ands some notice. I t is t h a t given in th e c u rren t issue of B.S.S. 229-1940, b u t th is Specification is a t present u nder revision. W hen revised it will be found to be g reatly expanded and clarified. So fa r as can be seen a t present, th e new B.S.S. 229 will not conflict in an y w ay w ith our Code, b u t, on th e contrary, will confirm its principles an d assist in its application.

A p o in t of difference betw een practice as preferred a n d p rev alen t among B ritish concerns an d t h a t laid dow n in th e A m erican codes concerns the use of arm oured cables. These are n o t accepted in dangerous areas in Am erica, b u t preferred in G reat B ritain . T he p o in t was referred b y th e C om m ittee to A m erican authorities, b u t th e reasons given in rep ly were not, in our opinion, entirely satisfactory, or sufficient to change our view.

FO R T H E PET R O L EU M IN D U STR Y . 385 I t emerged, however, th a t th e te rm “ arm oured cable ” has a different significance in Am erica from th a t in G reat B ritain, so it was considered desirable to include a definition of our classes of such cable, since we would perm it these, b u t not perm it those of th e A m erican description.

In view of th e special problem s surrounding th e use of flexible cables, a sub-section defining th e term s used in th is connection is included.

A section is given dealing w ith lightning protection term s in which both A merican a n d B ritish practice has been draw n upon, and an indication of th e source of each definition is given.

The definitions in th e section devoted to oilfield term s are necessarily open to argum ent, b u t it is believed th a t th e ir in te n t is clear, which is th e m ain consideration.

Section I I I . —Schedules.

I t is n o t possible in th e compass of a brief account to deal w ith th e explanatory Schedules in detail. E ach w ould w arran t a paper to itself for its adequate treatm en t.

All th a t will now be a tte m p te d is to m ention th e m ain purpose and points of each :—

Schedule A .— This gives a broad classification of dangerous atm ospheres as used in th e Code and a correlation of these classes w ith B uxton Groups (as a t present classified) for B ritish flam eproof ap p aratu s and w ith th e American N ational B oard of F ire U nderw riters’ classification of corre­

sponding explosion-proof apparatus.

This is to facilitate th e purchase of appropriate ap p aratu s from m an u ­ facturers in either country.

I t is pointed out th a t for th e m ajo rity of dangerous conditions encountered in th e petroleum industry, B u x to n Group I I or N .B .E .U . Class I Group D equipm ent is suitable.

The selection of suitable equipm ent for special conditions falling outside of th e above Groups will be simplified when th e revised B.S.S. 229 is' issued.

I t should be no ted th a t th e Code Class B— correlated w ith B uxton Group I I an d N .B .F .U . Class I Group D —includes vapour from petroleum having a flashpoint of 130° F . or less.

The figure to be ta k e n for th e lim iting flashpoint, and indeed th e desir­

ability of giving one a t all, was th e subject of a good deal of discussion, b u t it was finally included as representing safe practice an d affording a ready guide to th e m an on th e spot in assessing where th e dangerous area con­

ditions m ight apply.

Schedule B .—This is com plem entary to Schedule A, and indicates the m ain factors affecting th e degree of danger introduced into an atm osphere by th e presence of an inflam m able gas or vapour.

* I t points out th a t th e more readily-inflam m able gases m ay n o t in practice necessarily create th e m ost dangerous conditions. Hydrogen, for instance, although highly inflammable, will, because of its extrem e lightness, rise rapidly w ith little diffusion in still air, so th a t if electrical ap p aratu s be installed a t ground level and reasonably d ista n t from any p otential source of leakage of gas, and m eans are provided for th e ready escape of gas a t high level, it is unlikely th a t a dangerous atm osphere will accum ulate near th e electrical ap p aratu s.

386 MACLEAN : CODE OF ELE C TR IC A L PRA C TICE

T he im portance of la y o u t in regard to v en tila tio n to ensure t h a t danger­

ous gases are draw n aw ay from , a n d n o t tow ards electrical a p p a ra tu s is stressed.

D angerous conditions are show n to be m ost likely to arise w ith a gas or v ap o u r having high inflam m ability, wide range o f inflam m able concentration in air, den sity equal to or g reater th a n t h a t of air, low hu m id ity , a n d im properly directed v entilation.

A list of ty p ical gases a n d vapours encountered in th e petroleum industry classified to correspond w ith Schedule A is given.

Schedule G.—T his gives notes upo n incidence of risk of fire arising from electrical causes. I t points o u t t h a t for a fire or explosion to occur involving an electrical cause tw o factors m u st co-exist :

(а) There m u st be a d angerous a tm o s p h e re ; a n d (б) T here m u st be an electric spark, arc o r h o t spot.

I t th e n suggests th re e w ays of avoiding a dangerous com bination of these tw o factors. These are :—

(1) To suppress or elim inate en tirely th e dangerous atm osphere, in w hich case an electric sp ark can occur w ith o u t danger.

(2) Conversely, to elim inate or suppress en tirely a n y chance of an electric spark (or a flame resulting from it) reaching a surrounding dangerous atm osphere, in which case special a tte n tio n to th e sup­

pression or elim ination of such an atm osphere is unnecessary.

(3) To p a y a tte n tio n to b o th factors— i.e., th e suppression of the atm osphere an d th e elim ination o f th e sp ark or flame—to an extent in each case a n d in such a m anner t h a t th e com bined probability of th e ir occurring sim ultaneously is so rem ote as to be negligible.

One or other of th e first tw o m ethods is custom ary an d appropriate in th e m a jo rity of cases in refineries an d installations.

T h e th ird m ethod is one t h a t has been p erm itted in certain circumstances b y th e Code in oilfield practice only. H ere it can usually be arranged by th e ad option of custom ary suppressive m easures a t a well t h a t a dangerous atm osphere is norm ally unlikely to arise a t an y tim e, although it m ay do so occasionally.

I n th e sam e w ay, w ith non-sparking m otors a n d a p p a ra tu s a spark is sim ilarly unlikely to arise a t an y tim e, since all norm ally sparking parts are flam e-proof enclosed, although it m ay do so in th e abnorm al event of a fa u lt developing.

W ith such conditions th e com bined p ro b ab ility of th e tw o factors of danger arising sim ultaneously is v ery rem ote, an d th is com bination of precautions is considered to be adequate.

T he rules in tro d u ce safeguards, including th e use of gas-testing a p p a ratu s, to provide for conditions arising from failure of suppressive or safety m easures of either kind.

Discussions have revealed some confusion of th o u g h t an d a tendency to loose expression on th is subject, an d in view of its p rim a ry im portance, it seems desirable to dwell a little fu rth e r on it a t th is stage.

T he definition of dangerous atm osphere is clear an d sim ple. I t is :

“ A n atm osphere containing an y inflam m able gases or v ap o u r in a con­

FO R T H E PETR O LEU M IN D U S T R Y . 387 centration capable o f ignition by an electric spark or a rc .” An atm o ­ sphere a t an y place m ust, under th is definition, obviously be either safe or dangerous a t an y given m om ent of tim e.

As a step tow ards defining a dangerous area we have introduced and defined th e term ‘ dangerous location ” to fix a point from which th e ex ten t of a dangerous area shall be m easured.

A t th is stage a qualification is introduced. A dangerous location is defined as one where a leakage or emission of a product which can produce a dangerous atm osphere is normally likely to arise. I t should be noted th a t this does not m ean th a t a dangerous atm osphere is norm ally 'present or persisting. There is a persisting risk of its arising b u t not a persisting atmosphere. The decision as to where such conditions exist is of course a m a tte r for th e judgm ent of th e occupier.

In th e view of th e Com m ittee, confirmed by th e m ajor oil companies consulted, where th ere is a know n persisting—i.e., ever-present dangerous atmosphere— electrical ap p aratu s of any kind should be k ep t out of it.

W here, however, th ere is m erely a norm al or persisting risk or likelihood of such an atm osphere arising a t any tim e—though it is n o t usually present

—th e n th a t point is a dangerous location surrounded by a dangerous area, and th e appropriate electrical practice is flam eproof or th e equivalent.

W here th ere is a rem ote—i.e., infrequent or non-persisting—risk of a dangerous atm osphere arising, t h a t constitutes a rem otely dangerous location surrounded by a rem otely dangerous area, and th e stringency of th e electrical precautions m ay be correspondingly relaxed.

A brief sum m ary m ay help to clarify these notions and fix th em in m ind.

Given in decreasing order of danger we have :—-

(1) Continuously dangerous surrounding conditions : i.e., Dangerous atm osphere always present.

P ractice : N o electricity to be used.

(2) Dangerous surrounding conditions : i.e., D angerous atm osphere, although usually absent, norm ally likely to arise a t any tim e. This is th e usual case in refineries and installations.

Practice : F .L .P . or th e equivalent.

(3) Remotely dangerous surrounding conditions: i.e., U sually safe, b u t a dangerous atm osphere rem otely likely to arise in abnorm al circum stances th ro u g h failure of precautionary measures for its avoid­

ance. This is th e case in p arts of m any oilfields.

P r a c tic e : N on-sparking electrical ap p ara tu s w ith certain safeguards to provide against failure of preventive measures.

(4) Safe surrounding conditions: i.e., Dangerous atm osphere never present or likely to arise.

P ractice : In d u stria l equipm ent.

I t m ay be m entioned th a t since condition (I) above does not, in th e view of th e C om m ittee, perm it +he use of electricity it is n o t specifically m entioned in th e Code Rules b u t is referred to in th e Recom m endations.

The rem ainder of Schedule G deals specifically w ith conditions on oil­

fields. A n a tte m p t is m ade to classify oilfield areas into safe, rem otely dangerous, an d dangerous, so as to enable appropriate electrical practice to be applied a t an y place.

388 MACLEAN : CODE OF ELE C TR IC A L PRA C TICE

I n fram ing th e classification th e c o n tribution of danger b y each of th e following factors to a n y p a rtic u lar case is considered :—

(1) N ature of crude.— I t is assum ed th a t all crudes are capable of giving rise to a dangerous atm osphere if n o t confined a t th e surface.

(2) T ype of operation— i.e., drilling or producing. D rilling operations m ay be dangerous or rem otely dangerous, depending on m ethod and oth er factors, b u t never safe. Producing operations w ith a n open system are dangerous, b u t w ith a closed system only rem otely dangerous.

(3) Pressure in and depth below surface o f oil reservoir.—Pressure conditions are described as subnorm al, norm al, or abnorm al, depending on w hether th e pressure a t th e oil horizon is less th a n , equal to or greater th a n th e equivalent h y d ro sta tic head.

F o r purposes of assessing risk a t th e surface, th e first tw o classes—

i.e., subnorm al an d norm al— are grouped to g eth er a n d a m argin of perm issible excess pressure a t th e surface is provided b y tak in g salt w ater for calculating h y d ro static h ead an d th e n adding 150 lbs./sq. in.

before classing conditions as abnorm al.

T his reduces th e classes to tw o— viz., N orm al an d A bnorm al.

(4) T yp e o f drilling operation.—D istinctions are draw n between w ildcatting or exploring, outstepping, an d ex p lo itatio n or infiller, all of which are defined.

Combining th e above factors a n d considerations gives th e following classification of areas aro u n d oil wells :—

Dangerous areas—w ithin 50 feet of :—

(а) A producing well w ith open system o f p roduction (or any po in t where th e crude comes o u t in to th e open).

(б) A w ild-cat well th ro u g h o u t drilling operations.

(c) A n infiller well being drilled in a know n “ abnorm al ” area.

Remotely dangerous areas—w ithin 25 feet of :—

(a) A producing well w ith closed system of production.

(b) A n infiller well being drilled in a know n norm al area with an adequate closed system of drilling.

Other areas on oilfields are classed as safe or dangerous in accordance w ith th e general definitions of these term s.

In view of th e difficulty of laying dow n drilling an d producing methods considered a d eq u ate to ensure t h a t th e p o ten tially dangerous area around a well m ay be classed as rem otely dangerous, th e Code requires routine gas tests to be carried out near th e well in an area classed as rem otely dangerous, so t h a t should a dangerous atm osphere arise, th ro u g h th e failure or tem por­

a ry derangem ent of suppressive m easures, th is will n o t persist unobserved.

On such an atm osphere being observed th e Code requires electricity to be cu t off from all b u t F .L .P . or equivalent equipm ent u n til conditions have again been b ro u g h t under control.

I t m ay be m entioned t h a t routine gas-testing accords w ith th e practice of one m ajo r oil com pany w hich has extensively applied electric drilling .and oilfield electrification generally. T heir experience indicates th a t, owing to th e open n a tu re of th e rigs em ployed, a n d using ad eq u ate sup­

pressive m easures in a norm al area, a dangerous atm osphere, if it arises,

FO R T H E PET R O L EU M IN D U STR Y . 389 rarely trav els more th a n a few feet from th e point of its emission before safe dispersion occurs. This experience supports th e adoption of 25 feet as th e radius of ex te n t for a rem otely dangerous area.

The electrical precautions described in Schedule G call for little com­

m ent ; th e y m erely indicate th e relaxation of com pletely F .L .P . or equi­

valent ty p e construction th a t is admissible in a rem otely dangerous area, and th a t th is perm its of a w ider application w ith safety and economy of modern m ethods of electric drilling th a n would otherwise be possible.

Schedule C .— This deals w ith th e question of static electricity other th a n lightning. Much of th e inform ation given in it has been draw n from Circular No. C 438, d a te d 1942, issued by th e U.S. D epartm ent of Commerce, N ational B ureau of S tandards, an d from a paper read by J . M. Pearson of th e Sun Oil Co., Philadelphia, to th e A m erican Petroleum In stitu tio n in Chicago in 1940.

T he early p a r t of th e schedule describes in a non-technical m anner th e commonly accepted basis of th e phenom ena associated w ith th e generation, accum ulation, an d discharge of static electricity. The unexpected dangers th a t m ay arise from induced an d bound charges are described.

We need n o t here concern ourselves w ith th e technical aspects of static, b u t m ay refer briefly to some of th e practical points arising from them .

As a p articu lar source of danger, among others, it is shown th a t when a composite stream of light petroleum liquid and an immiscible contam inant such as w ater flows th ro u g h a pipe, especially a t high velocity, th e particles are altern ately pressed together a n d to rn ap art, also similarly pressed against an d to rn aw ay from th e pipe wall. The result is th a t a charge of one sign is accum ulated on one liquid and a charge of opposite sign on the other. I f th e pipe is long enough, an equilibrium condition is reached a t which leakage and recom bination of charges equals th e rate of th eir production.

E xperim ents carried out a t Delft, H olland, and elsewhere have d eter­

mined th e order of value of charges and potentials obtainable in this way.

The m axim um observed current flow carried by th e stream corresponds to about 1-7 X 10-9 am peres per gallon per m inute of flow.

I t is found th a t a t velocities below ab o u t 3 ft./sec. no charge accum ulates.

Such charges are n o t in general im p o rtan t in th e pipeline, although this should be earth ed for th e safe discharge of bound charges on th e pipeline when th is is drained, or th e contents changed, b u t th e y become im portant when discharged into tanks.

H ere th e liquids separate. T he heavier—usually w ater—takes one charge w ith it to th e bottom , where it can be drained aw ay by earthing.

The other expands like a gas through th e body of th e oil. Some of it reaches th e ta n k walls on th e w ay up, th e rem ainder rises to th e surface. The only p a th for th is to th e m etal wall, whence it can flow round to be neutralized, is across th e oil surface. I f th e surface resistance is high, th e rate of leakage across it m ay be less th a n th e in p u t of fresh charges. In such a case th e p o tential will rise u ntil a flash-over occurs. W ith lighter spirits th e atm osphere in th e vapour space will usually be too rich to ignite, b u t w ith oils in th e kerosine range th is is n o t usually so and a fire m ay result.

Safeguards for these conditions are set out in th e Schedule and th e R ules.' T hey include n o t only intelligent earthing, b u t such suggestions as the introduction of incoming stream s low down in tanks.

390 MACLEAN : CODE OF E L E C TR IC A L P R A C TIC E

T he problem s presented b y different ty p es of ta n k s are discussed, and precautions ap p ro p ria te to each described.

T he la te r p a rt of th e schedule describes conditions arising during the filling an d em ptying of ro ad -and rail cars, an d shows th e benefit of careful a tte n tio n to earth in g an d o th e r precautions before a n y oil is perm itted to flow in to or o u t from such containers.

T he process of th e building up of sta tic charges on ro a d cars b y th e passage of ty re s over th e ground is described. T his trouble, as indeed all static troubles, is little in evidence in norm ally hu m id atm ospheres, b u t m ay be a serious source of danger in v ery d ry clim ates of, say, 60 p er cent, or less relativ e h u m id ity .

A n oil com pany has given p articu lars of a fire t h a t occurred on one of th e ir refineries in th e M iddle E a st. I t was established t h a t th is arose from a discharge of sta tic electricity accum ulated th ro u g h th e im pingem ent of a stream of oil on to a splash p late. T h ey carried o u t a series of experiments duplicating th e conditions b u t a t various hum idities. A t relative hum idi­

ties above 55-57 per cent, th e sparking disappeared altogether, b u t a t lower h um idities th e sparking was dangerous an d caused ignition.

Schedule D .—Deals w ith pro tectio n against lightning. Owing to the g re at v a riatio n in conditions of all kinds affecting th is problem , few rules can be laid dow n to be of general application.

I t is p ointed o u t th a t th e e x te n t to w hich it m ay be desirable or necessary to p ro te c t buildings or stru ctu re s will depend on a n assessm ent of the following factors :—

(1) T he freqdency an d severity of th u n d ersto rm s likely to occur in th e locality concerned.

(2) T he degree an d e x te n t of danger to life of operating personnel or occupants of an y building or stru c tu re arising from its susceptibility to being stru ck b y hghtning.

(3) T he im portance a tta c h e d by th e owners to dam age or destruction b y hgh tn in g of an y p a rtic u lar building or stru ctu re.

(4) T he possibility of a fire spreading to neighbouring pro p erty and th e im portance a tta c h e d to this.

(5) A ny local regulations w hich m ay require hgh tn in g protection in an y p articu lar case.

(6) T he n a tu re of th e soil an d th e pollution of th e atm osphere.

Reference is m ade to th e following p ubhcations dealing v ery fully with th e practice to be apphed :—

(a) “ Code for P ro te ctio n against L ig h tn in g .” N atio n al Bureau of S tan d ard s H andbook H . 21 issued 2nd N ovem ber, 1937, by U.S.

D e p artm en t of Commerce.

(b) “ P ro tec tio n of S tru ctu res against L ig h tn in g .” B ritish Standard Code of P ractice C .P.I. 1943.

The various principles a n d practice to be app h ed to stru ctu res where, afte r an assessm ent of th e requirem ents of th e case, it is decided th a t

•protection is desirable, are described in considerable detail. P articu lar a tte n tio n is given to th e case of oil tan k s, m ost of w hich of m odern design

are found to be self-protecting.

FO R T H E PET R O L EU M IN D U STR Y . 391 W here protection is applied, stress is laid upon regular testing of th e protective system . This is im p o rtan t, as e a rth resistance will usually v ary greatly th ro u g h o u t th e year in any locality n o t always waterlogged.

Schedule E .—This schedule is largely a precis of electrical protective system s an d devices. I t draw s a tte n tio n to th e differences in th e require­

m ents of such devices w hen applied to system and p lan t protection.

I t arose o u t of discussions on th e desirability or otherwise of a growing tendency to p u t forw ard e arth leakage protection as a general safety measure. T he Com m ittee were n o t entirely hi agreem ent w ith this tendency, an d a m ain purpose of th e schedule was to indicate th e various forms of such protection and th eir lim itations, and to p u t them into some perspective w ith other forms.

I t is hoped t h a t th is question will be clarified by discussions a t present proceeding in com m ittees of other In stitu te s. M eantime, excepting in connection w ith certain applications of flexible cables, th e Code does not make th e use of e a rth leakage protection obligatory.

I t is felt t h a t in its present form th is schedule is n o t entirely appropriate to the Code, an d since it gives rise to no m an d ato ry Rules, it m ay eventually be om itted or considerably revised.

Some discussions on th e question of e a rth leakage protection by those present th is evening w ould be helpful in arriving a t a decision on this question.

Schedule F .—This deals w ith th e use of flexible cables in dangerous areas. A t th e o u tset it is stressed th a t, wherever practicable, an electrical installation should comprise fixed ap p a ratu s an d perm anent wiring of appropriate ty p e.

I t is recognized, however, th a t this is n o t always practicable, and appro­

priate types of cables, fittings, a n d m ethods of connection are described.

One prevalent source of danger has been flexible cables or so-called

“ cords ” connected to th e m ains and used w ith portable handlam ps.

Although th is question has received, and is now receiving, prom inent atten tio n it has not, in th e view of th e Committee, y et been satisfactorily solved, an d th e y have therefore m eantim e forbidden th e use of such a m ethod of lighting in dangerous areas, although it is p erm itted in American practice.

The cases where earth-leakage protection and electrical interlocking are considered desirable are described a n d th e in te n t of th e rules in these con­

nections is explained. To a large ex ten t m odern coal-mining practice has been followed, b u t it m ay be no ted th a t th e Code requirem ents in this particular case regarding provision against earth leakage are somewhat more stringent th a n those laid down in th e Mines Regulations (Amendments).

The im portance of regular inspection and adequate m aintenance of all flexible cables is stressed.

Section I V .—Rules.

These are divided into four m ain series :—■

Series 100 are of general application, and are subdivided into those th a t ap p ly in any area and those th a t are specific to a dangerous area.

Series 200 deal w ith precautions for th e avoidance of danger from static in relation to process p lan ts, pipelines, ta n k s, ships, ro a d or rail vehicles, an d so on w here a dangerous atm osphere m ay be present or arise.

Series 300 deals w ith pro tectio n against lightning in relatio n to oil ta n k s, buildings, a n d telephone lines w here a dangerous atm osphere m ay arise.

Series 500 is d evoted solely to oilfields, an d therefore is largely concerned w ith relax atio n in electrical safe ty precautions permissible in rem otely dangerous areas, a n d in sta tin g th e safeguards under w hich th is relax atio n m a y be applied. T his series is still under con­

sideration b y th e m ajor oil com panies, an d will no d o u b t a t least require final editing.

S hort of quoting th e R ules in full, th ere is little t h a t can be said about th em , as all are im p o rta n t.

I t m ay, however, be said t h a t th e y do n o t conflict w ith th e in ten t of those issued b y th e P etro leu m In stallatio n s C om m ittee so far as these apply.

Section V.—Recommendations.

This is a v ery sh o rt section. I t comprises a few suggestions, which arose o u t of discussion, for possible rules, b u t w hich it was decided should not be given m a n d ato ry statu s.

P erh ap s th e m ost im p o rta n t is th e last, w hich recom m ends th a t electricity shall n o t be used in a know n persisting dangerous atm osphere.

Co n c l u s i o n.

I t will be ap p reciated th a t th is p ap er deals w ith th e Code in its present d ra ft stage, an d t h a t its order a n d co n ten t m ay be am ended during final editing.

392 CODE OF ELE C TR IC A L PR A C TIC E FO R T H E P E T R O L E u lii a -'.jj-j.j a —^ .

393

THE INSTITUTE OF PETROLEUM.

A m e e t i n g oi th e In s titu te of Petroleum was held a t Manson House, 26 P o rtla n d Place, London, W .l, on W ednesday, 9th May, 1945. Thé President, Professor P . H . G arner, was in th e Chair.

A pap er on Code of E lectric P ractice for th e Petroleum In d u stry ” was read by Mr. A lan D. Maclean. [See pp. 379-392.]

D IS C U S S IO N .

T h e P r e s i d e n t co m p lim e n ted M r. M aclean on th e ab le m an n e r in w hich he h a d accom plished th e fo rm id ab le ta s k of p re se n tin g th e su b ject.

R eferrin g to Schedule B of S ectio n I I I , w hich d e a lt w ith d an g ero u s atm o sp h eres, th e P re sid e n t co m m en ted o n th e fa c t th a t, a fte r considerable discussion, th e flash ­ p o in t chosen fo r v a p o u r w as 130° F . H e a sk ed M r. M aclean to enlarge on th e reasons w hy t h a t p a rtic u la r te m p e ra tu re w as chosen, a n d w h e th er it sh o u ld d ep en d on th e p a rtic u la r atm o sp h e ric te m p e ra tu re in volved. T h u s, for tro p ic a l clim ates, p e rh a p s a different te m p e ra tu re m ig h t h a v e b een chosen fro m t h a t ap p ly in g to te m p e ra te clim ates.

H e also a sk ed for a brief d esc rip tio n of th e difference b e tw een th e A m erican a n d B ritish cables re fe rre d to b y M r. M aclean.

M r . A l a n D . M a c l e a n , a f te r th a n k in g th e P re sid e n t on b e h alf of him self a n d th e m em bers of th e S ub -C o m m ittee fo r h is v e ry k in d in tro d u c to ry re m ark s, rep lied t h a t th ere h a d b een m u ch discussion b efore 130° F . w as fixed as th e flash p o in t for v ap o u r.

A fter th e m a tte r w as discussed it w as re fe rre d b a c k to th e v a rio u s com panies, an d one opinion w as t h a t kerosine co u ld n e v e r p ro d u ce a d a n g ero u s c o n d itio n in th e v a p o u r space. T h a t, how ever, w as n o t t r u e ; if th e re w ere a fire, one of th e m o st dangerous th in g s w as a n e m p ty k erosine ta n k . T h e S ub-C om m ittee h a d d ecided a t one tim e t h a t it co u ld n o t p u t fo rw a rd a n y figure t h a t w as u n ifo rm ly accep tab le.

One large oil co m p a n y to w h o m th e m a tte r w as referred h a d s ta te d t h a t th e ir p ra ctic e w as to a d o p t th e figure of 130° F . ; a n d th is w as ad o p te d . I t w as n o t m a n d a to ry , b u t illu stra te d , fo r ex am p le, w h a t p ro d u c ts of h ig h er flash, such as fuel oils, w ere u nlikely to give rise to explosive co n d itio n s in th e v a p o u r space.

I n re p ly to th e P re s id e n t’s q u e stio n concerning cables, th e ty p e of cable th e Sub- C om m ittee h a d in m in d w as a 3-core cable, p a p e r-in su la te d a n d lead-covered. T he A m erican arm o u re d cab le w as u su a lly a V .I.R . m u lti-co re cable, sh e a th e d w ith a flexible m etallic tu b in g ; or a t a n y ra te , it looked like th a t. A considerable n u m b er of te s ts , com p risin g p re ssu re a n d o th e r te s ts , w as specified for th e flexible tu b in g . B u t w h ereas th e arm o u rin g on th e B ritish cable w as a b u ilt-u p a rm o u rin g , th e A m erican cable w as d ra w n in to its arm o u rin g , a n d in th e view of th e S ub-C om m ittee w as n o t s a tis fa c to ry to use for flam eproof purposes. O n th e o th e r h a n d , th e a rg u ­ m en ts u sed a g a in st th e B ritish arm o u re d cable w ere considered b y th e S ub-C om m ittee to be q u ite in v alid .

T he m a tte r w as re fe rre d to th e A m erican N a tio n a l B o a rd of F ire U n d erw riters, w ho h a d s ta te d th e ir ad h eren ce to th e view t h a t rigid c o n d u it w as th e only s a tis ­ fa cto ry th in g to use in d an g ero u s areas. T h ey h a d p o in te d o u t t h a t th e degree of s a fe ty in a h a za rd o u s lo ca tio n w as d e p e n d e n t on th e a b ility of th e arm o u red cable to w ith s ta n d m ech an ical in ju ry a n d to p re v e n t flam e or sufficient h e a t being t r a n s ­ m itte d to th e s u rro u n d in g a tm o sp h e re to c rea te h a z a r d ; th e y b elieved t h a t a rigid c o n d u it w as b e st able to resist.

T he S u b -C o m m ittee d isagreed w ith t h a t view , how ever, a n d a fte r s tu d y of th e A m erican specification fo r a rm o u re d cable, h a d agreed t h a t it w as u n su itab le. T he c om parison, th ere fo re, w as re ally b etw een th e B ritish arm o u red cable a n d solid- d ra w n tu b e arm o u rin g . T h e ty p e of arm o u rin g w hich c onsisted of flexible m eta l tu b in g h a d n o t th e p ro p e rtie s t h a t we re q u ire d in o u r a rm o u re d c ab les; th e m u lti­

core cab le w as ju s t p u lle d in to a flexible tu b e .

394 MACLEAN : CODE OE ELE C TR IC A L PR A C TICE

Mr. R . R . T w e e d , reca llin g h is e a rlier a sso ciatio n s w ith th e la te M r. C h risto p h er D ailey , w ho w ou ld h a v e b een d e lig h te d b y th e re s u lts w h ich h a d b e e n a ch iev e d by th e I n s t i tu t e ’s S u b -C o m m ittee , said t h a t w h e n T rin id a d w as a b o u t to a d o p t th e ir ow n code of e le ctrical p ra c tic e , M r. D a ile y h a d u rg e d th e m to a w a it th e code w hich w as b ein g p re p a re d b y th e I n s t i tu t e fo r th e w hole in d u s try , a s h e k n ew t h a t it w ould be a w o rk of som e v alu e. E v e n ts h a d p ro v e d t h a t M r. D ailey w as p e rfe c tly justified, a n d one could o nly h o p e t h a t th e code w o u ld be c o m p le te d a n d p r in te d a n d placed in th e h a n d s of th e C olonial Office a s soon a s possible. M r. T w eed c o n g ra tu la te d M r. M aclean a n d h is colleagues o n th e S u b -C o m m ittee fo r th e g re a t w o rk th e y h ad done.

M r . M a c l e a n e x p ressed h is a p p re c ia tio n of M r. T w e ed ’s re m a rk s, a n d said it was a m a tte r fo r g re a t re g re t t h a t M r. D a ile y h a d n o t liv e d to see th e w o rk th ro u g h .

Mr. H . F o s s e t t a sk e d if M r. M aclean co u ld e x p a n d h is re m a rk s on th e definition of a d an g ero u s a re a o r lo c a lity , fo r d efin itio n seem ed to b e a tr ic k y p ro b lem . F or e x am p le, referen ce h a d b e en m a d e to th e specific d ista n c e of 50 ft. a ro u n d a well or o th e r p la n t as d e lin e a tin g a d a n g ero u s a re a in c e rta in co n d itio n s. H e w ondered w h e th e r th e S u b -C o m m ittee co u ld co n sid er th e e x te n sio n of th e d efinition of a d an g ero u s a rea . H e h a d in m in d , fo r ex am p le, th e sto ra g e of liquefied gas, and en v isag e d a m ish ap ' in a p re ssu re sto ra g e ta n k w h ich co u ld in d u ce a d an g ero u s area of v e ry m u ch g re a te r e x te n t u n d e r th e influence of e x te rn a l fa cto rs, su ch as w eather c o n d itio n s (h u m id ity , a n d so on). H e co u ld visu alize d a n g e ro u s c o n d itio n s existing o v er a n a re a e x te n d in g h u n d re d s of feet fro m th e p o in t a t w h ich th e gas w as released.

M r. M a c l e a n re p lied t h a t th e p ro b lem of re la tin g th e size of a d a n g ero u s area to th e p a r tic u la r c o n d itio n s g iv in g rise to th e d a n g er, r a th e r t h a n defining a dangerous a re a as b e in g th e a re a w ith in a circle of g iv en d ia m e te r, w as th e c ru x of th e whole p ro b lem , a n d h a d given rise to m o re d iscussion a m o n g th e m em b e rs of th e Sub­

c o m m itte e th a n h a d a n y o th e r m a tte r . T h ey h a d tr ie d to giv e a definition of a d an g ero u s a re a w h ich w ould b e of u n iv e rs a l a p p lic a tio n . A rticle s h a d been p u b ­ lish ed in th e tec h n ica l p re ss re c e n tly , som e fro m A m e ric a a n d o th e r co u n tries, sug­

g estin g t h a t su ch fa cto rs as le n g th , b re a d th , a n d h e ig h t of b u ild in g s, as well as pre­

v a ilin g w ind, sh o u ld be co n sid ered in a rriv in g a t a decision as to th e definition of a d an g ero u s area. B u t th e S u b -C o m m ittee co n sid ered t h a t to a sk a n y occupier to go in to all th o se fa cto rs befo re decid in g to ta k e p re c a u tio n s in a n y a re a w as to ask too m u c h ; i t w ou ld b e m u c h to o acad em ic. T h e S u b -C o m m ittee h a d b een governed to som e e x te n t b y th e P e tro le u m In s ta lla tio n C o m m itte e ’s ru lin g , a f te r t h a t com­

m itte e h a d co n sid ered th e m a tte r carefu lly . Som e of th e Oil co m p an ies had , as a ro u g h guid e, defined a d an g ero u s a re a as w ith in 100 ft. fro m th e p o in t of probable em ission of a d an g ero u s a tm o s p h e re ; o th e r co m p an ies h a d a d o p te d o th e r distances.

T h e S u b -C o m m ittee h a d c o n sid ered t h a t 50 ft. w as th e m in im u m d ista n c e it could safely re c o m m e n d ; a t th e sam e tim e , for all th e a p p lic a tio n s w h ich th e Sub-C om m ittee co u ld th in k of, it w as a safe m a x im u m . I f th e re w ere w in d , th e re w ou ld be rapid d is p e rs io n ; a n d i t w as o n ly a w in d w h ich w o u ld d is to rt th e sh a p e of th e dangerous a re a fro m th e circu lar. In a s m u c h as te s ts h a d in d ic a te d t h a t u su a lly a n inflam m able m ix tu re d isp ersed w ith in a d istan c e of 5 ft., a n d p ra c tic a lly n e v e r p e rsiste d beyond t h a t d istan c e, it w as reaso n a b le to say t h a t 50 ft. w as w ell b e y o n d th e d istan c e w ithin w h ich a d e q u a te d ispersion w ould occur. T h e y d id n o t ta k e a cc o u n t of th e n atu re of th e source of th e d a n g e r a s a fa c to r e x te n d in g th e a re a of d a n g er. H e gathered t h a t M r. F o s s e tt h a d in m in d th e sto ra g e of gases u n d e r p re ssu re , a n d th e possible b u rs tin g of th e c o n ta in ers.

Mr. Fo s s e t t s a i d h e w a s t h i n k i n g o f s t o r a g e a t p r e s s u r e s u p t o , s a y , 3 0 l b s . M r . M a c l e a n su g g este d t h a t in su ch a case th e o ccu p ier w o u ld ta k e p recau tio n s, a n y h o w , in d e signing th e c o n ta in e r to s u it th e p re ssu re , a n d h e d o u b te d v e ry m uch t h a t it w a rra n te d q u alify in g th e defin itio n . T h ere a p p e a re d to b e som e confusion of id eas in th is m a tte r . W e w ere n o t co n cern ed w ith how fa r th e in flam m ab le con­

te n ts of such a c o n ta in e r m ig h t tra v e l sh o u ld it b u rs t, n o r w ith th e d ista n c e th a t th e effects of a n ex plosion in it, u n d e r such a m ish ap , m ig h t e x te n d . W e w ere con­

cern e d in defining h o w n e a r a s p a rk m ig h t b e b ro u g h t to it w ith o u t ig n itin g norm al