Maritime University of Szczecin
Akademia Morska w Szczecinie
2011, 27(99) z. 1 pp. 131–138 2011, 27(99) z. 1 s. 131–138
Method of risk assessment of optical radiation emitted
on workers by machines
Metoda oceny zagrożenia pracowników promieniowaniem
optycznym emitowanym przez maszyny
Andrzej Pawlak
Central Institute for Labour Protection – National Research Institute Centralny Instytut Ochrony Pracy – Państwowy Instytut Badawczy 00-701 Warszawa, ul. Czerniakowska 16, e-mail: anpaw@ciop.pl
Key words: ultra-violet, visible and infra-red radiation Abstract
This paper presents assessment methods for machinery emitting optical radiation. The method is based on described in standard PN-EN 12198 Part 1 and 2 measurements of ultraviolet, visible or infrared radiation parameters. The results of the measurements determine category of radiation emission for certain machinery. Then the example machineries where technological processes use ultraviolet, visible or infrared radiation are presented.
Słowa kluczowe: promieniowanie nadfioletowe, widzialne i podczerwone Abstrakt
W referacie przedstawiono metodę oceny maszyn emitujących nielaserowe promieniowanie optyczne: nadfio-letowe, widzialne lub podczerwone. Ocena ta dokonywana jest podczas obsługi, nastawiania i konserwacji maszyny. Na podstawie tych pomiarów wyznaczana jest kategoria emisji promieniowania w skali od 0 do 2. W artykule przestawiono także przykładowe maszyny, w których procesach technologicznych wykorzysty-wane jest promieniowanie nadfioletowe, widzialne lub podczerwone. Dokonano również oceny zagrożenia promieniowaniem optycznym na stanowiskach obsługi wybranych maszyn, zgodnie z kryteriami obowiązują-cymi w naszym kraju.
Introduction
Many machines exploit optical radiation (ultra-violet, visible and infrared) for technological pur-poses, including among the others photopoli-merization, curing, drying or disinfection. Such machines are used in e.g. printing, chemical proc-essing, pharmaceutics, food processing or furniture industries. Optical radiation may be harmful to eyes and skin of employees working on such machines, when excessive quantities of such radiation are released outside of the machine into the area where people are present. According to data from Central Statistical Office for 2006, (based on the Z-10 card) the number of employees exposed to exces-sive ultraviolet radiation was estimated to be equal
to 2761 and 6026 employees were exposed to excessive infrared radiation, which means that approximately 8800 registered employees were exposed to radiation levels exceeding the values allowed by NDN. Unfortunately, these numbers do not reflect the total number of employees exposed to dangerous levels of radiation, since e.g. the total number of employees exposed to man-generated ultraviolet radiation back in 2002 was estimated to be equal to 91.5 thousand (based on the national Census). The majority of the aforementioned em-ployees are exposed to radiation due to machine operation. This fact is accounted for in Directive 89/655/EWG [1], which define the need to restrict ultraviolet radiation emissions from machines and carry out its evaluation. A manufactured machine
may be evaluated for its safety in terms of emis-sions of ultraviolet radiation, under the standard aligned with the machine directive (PN-EN 12198 [2, 3, 4]).
Assessment methods for machines emitting incoherent optical radiation
The machine assessment method in terms of (among the others) emission of incoherent optical radiation is included in three clauses of the PN-EN 12198 standard. The PN-EN 12198-1 [2] standard contains guidelines for manufacturers related with design of safe machines, when type C safety standards do not apply. This text covers the generic approach for assessment of any risks related with emission of optical radiation by designed machines and describes means of their limitation. Next, machine classification in terms of the levels of optical radiation is presented, together with the generic design requirements. Annex B contains description of measurement conditions, basic characteristics of measurement sensors and rela-tionship between the level of emitted radiation and machine category. This standard also defines requirements for protective means used to eliminate or diminish risks related with emission of optical radiation, while Annex C covers examples of means used to eliminate or diminish exposure to optical radiation.
Standard PN-EN 12198-2 [3] defines measure-ment methods for any quantities related with optical radiation emitted by machines. It also includes requirements related with location of measurement points and measurement duration. Annex A.2 describes measurement techniques for various types of optical radiation.
Standard PN-EN 12198-3 [4] defines means allowing machine manufacturers design and pro-duce effective means of technical protection against optical radiation as well as screen design strategies.
General approach
Based on notes included in Directive 2006/42 [5], a machine must be designed and manufactured in such a way that any emissions of optical radia-tion are diminished to the level required by the machine’s operation, while eliminating the influ-ence of such radiation on exposed people, or dimi-nishing its influence to safe levels. Following this guideline, as well as requirements included in stan-dard PN-EN 12198-1 [2], machine manufacturers ought to identify any optical radiation emissions and assess risks causes by such emissions. When
needed, a manufacturer ought to employ all means necessary to diminish related risks by applying appropriate attenuating or screening materials. Next, it is necessary to perform verification mea-surements in order to assess the occurrence of any related risks. The risk assessment ought to cover any possible human exposure vectors in terms of ultraviolet radiation emitted by the examined machine, occurring at any stage of its technical life. Annex A in the aforementioned standard defines the following stages of technical life for a machine: construction;
transport and approval for exploitation (assem-bly, installation, adjustments);
exploitation (configuration, programming or changes to the production process, operation, cleaning, defect detection, maintenance and repairs);
decommissioning and disassembly.
Method for determining machine category
Determination of the machine category in terms of emission of optical radiation is carried out in relation to individual stages of machine’s exploita-tion process i.e. service, configuraexploita-tion and cleaning. The given machine is attributed with the highest category for the optical radiation emission found for any stage of the machine's exploitation process. According to table 1, there are three radiation cate-gories.
Table 1. Classification of machines in terms of optical radiation emission levels [2]
Tabela 1. Klasyfikacja maszyn ze względu na poziom emisji promieniowania [2]
Category Limitations and pre-ventive means Information and trainings 0 No limitations No need to inform
1
Limitations: restricted access, special protec-tive means may be needed
Information on potential threat, risks and secondary effects
2
Requires special limi-tations and protective means
Information on potential threat, risks and secondary effects: special training might be necessary
The relationship between parameters for ultra-violet, visible and infra-red optical radiation attri-buted to the given machine and the machine emis-sion category is shown in table 2, 3 and 4, respec-tively. In case of ultraviolet radiation, the effective radiation intensity Eeff or the spectral radiation
intensity E must be determined. The measurement
with the possibility of shortening this period when the same results are obtained. The relative spectral effectiveness curve for ultraviolet radiation S() is defined in Annex B to the standard PN-EN 12198-1 [2].
Table 2. Relationship between the effective irradiation intensity for ultraviolet radiation and the machine radiation emission category [2]
Tabela 2. Zależność między skutecznym natężeniem napro-mienienia promieniowaniem nadfioletowym a kategorią emisji promieniowania maszyny [2] Eeff (180 nm 400 nm), [W/m 2] Category Eeff ≤ 0.1·10–3 0 0.1·10–3 < E eff ≤ 1.0·10–3 1 Eeff > 1.0·10–3 2
In case of visible radiation, the effective angle of view for the radiation source must be determined in the measurement location . For angles < 11
mrad, it is necessary to determine the effective irradiance Eeff, while for angles ≥ 11 mrad it is
necessary to determine the effective radiance Leff.
The relative spectral efficacy curve S() for wave-lengths between 400 and 700 nm is defined in Annex B to the aforementioned standard. The measurement ought to be averaged over the period of 8 hours, with the possibility of shortening this period when the same results are obtained.
Table 3. Relationship between the effective irradiance or effec-tive radiance for visible radiation and the machine radiation emission category [2]
Tabela 3. Zależność między skutecznym natężeniem napro-mienienia lub skuteczną luminancją napronapro-mienienia promie-niowaniem widzialnym a kategorią emisji promieniowania maszyny [2] Eeff (400 nm 700 nm) [W/m2] Leff (400 nm 700 nm) [W/m2sr–1] Category Eeff ≤ 1.0·10–3 10 0 1.0·10–3 < E eff ≤ 10·10–3 100 1 Eeff > 10·10–3 > 100 2
However, in the case of infra-red radiation, it is necessary to determine the irradiance (E) without application of spectral weighting. The measurement ought to be averaged over the period of 10 seconds.
Table 4. Relationship between the irradiance for infra-red radiation and the machine radiation emission category [2] Tabela 4. Zależność między natężeniem napromienienia pro-mieniowaniem podczerwonym a kategorią emisji promienio-wania maszyny [2]
E (700 nm 1 mm), [W/m2] Category
E ≤ 33 0
33 < E ≤ 100 1
E > 100 2
The measurement of the appropriate parameters of emitted ultraviolet, visible and infra-red radiation ought to be always carried out at the distance of 0.1 m from the machine access surface, in the direc-tion of the maximum radiadirec-tion intensity. In cases where the machine body includes holes of sufficient size for employees to introduce their limbs, the measurement process ought to be carried out within the region accessible to an employee. If employees are required to peer inside of the machine body through e.g. special windows, the measurement process ought to be carried out in locations corre-sponding to eye position during normal operating conditions. Additionally, it is also necessary to carry out measurements in locations, where radia-tion emission is possible (e.g. due to transmission through gaps in the body, or in areas of wall joints etc.) and within any housing elements dismounted for maintenance purposes or holes used during maintenance and repair processes. All measurement points ought to be determined in such a way, that they can be unequivocally recognized.
Examples of machines emitting ultraviolet radiation
Packaging machine type 234 KSP, used in food processing industry
This machine has the total of 5 UV-C radiators (fluorescent lamps) installed, representing the source of a potential exposure to ultraviolet radia-tion in the UV-C range during the regular operaradia-tion of the machine in question, as well as during acci-dental exposure of staff in the vicinity of the ma-chine during its disinfection. The number and the total power of UV-C lamps are different for two operating modes of this machine. During the nor-mal operation, the following radiators are switched on:
• TUV PL-L 18 W – used to disinfect plastic packaging (cups),
• TUV TL-D 55 W (2 pieces) – used to disinfect aluminium cup lids.
In the disinfection mode, two radiators type TUV TL-D 15 W are enabled. These radiators are installed in the upper part of the machine, in the vicinity of the side walls (see figure 1). The ma-chine is shielded with a housing made of protective screens made from transparent polycarbonate resin. There are substantial gaps between individual screens, allowing the UV radiation pass freely to the surroundings. Effectively, this represents the potential threat to both staff operating this machine (permanent work posts), as well as staff passing by the machine, which is located at the communication zone.
In order to evaluate the UV radiation risk for staff operating this machine, measurements of the effective irradiance for this type of radiation were carried out, both for the normal operating condi-tions, as well as the disinfection mode. The mea-surement of the ultraviolet radiation parameters was carried out in compliance with the method defined in standard PN-EN 14255-1: 2010 [6] and the obtained measurement results were compared with the limiting exposure values (NDN) included in the decree [7]. This measurement was carried out using a radiometer equipped with a detector head cor-rected to the relative biological effectiveness of ultraviolet radiation S().
Fig. 1. Side view of the type 234 KSP machine from the side of the cup loading bay with enabled UV radiators in the upper part (machine rear); source: author’s photograph
Rys. 1. Widok automatu typ 234 KSP od strony załadunku kubków z załączonymi promiennikami UV w górnej części – tył automatu; źródło: fot. autor
During the regular operation of this machine, the examined work posts feature potential threat of exposure of eyes and face skin, as well as hands of staff to UV-C radiation reflected in a directional manner and dissipated on various metal (glossy) elements located inside of this machine. Measure-ments were conducted in locations, where staff carries out the following actions:
loading cups (front of the machine) (Fig. 2a), loading cup lids (rear of the machine) (Fig. 2b).
Measurements were carried out for the unpro-tected body parts of staff, exposed to UV radiation i.e. eyes, face skin and hand skin, in locations cor-responding to their typical location during work. Each aforementioned body part was examined through a series of measurements, the result of which were then averaged to obtain the average irradiance.
According to the information provided by the employer, the average exposition time for staff during a shift was equal to:
• 6 hours (21 600 seconds) – when loading cups, • 0.5 hours (1800 seconds) – when loading cup
lids.
Results for measurement of irradiance for ultraviolet radiation
Results for measurements and calculations needed to assess the UV radiation exposure risks for staff are presented in table 5. The estimated, maximum acceptable exposure times are presented in table 6. The obtained values of effective irradi-ance for all exposed body parts for staff (under
a) b)
Fig. 2. Side view of the type 234 KSP machine from the side: a) of the cup loading bay (front of the machine), b) of the cup lid load-ing bay (rear of the machine); source: author’s photograph
Rys. 2. Widok automatu typ 234 KSP od strony: a) załadunku kubków – przód automatu, b) od strony załadunku platynek – tył automatu; źródło: fot. autor
the maximum exposure time per shift, as declared by the employer) indicate high professional risk related with substantial over-run of acceptable values (approximately 5 times for eye and face skin and approximately 10 times for hand skin). Such over-runs were observed for the process of cup loading, which is carried out at the front of the machine. Due to the fact that the process of cup lid loading (rear of the machine) is carried out by the same employee, the received UV radiation doses for both process are additive even though the effec-tive irradiation values during the process of cup lid loading are much lower than the NDN value.
During the process of loading cups (front of the machine), the determined acceptable exposure time without the use of personal means of protection is down to only 34 minutes. When the total exposure time exceeds 34 minutes, it is necessary to use the appropriately selected personal means of protec-tion. During the process of loading cup lids (rear of the machine), the determined acceptable exposure time without the use of personal means of protec-tion is down to only 131 minutes. Considering that the maximum exposure time in this process per shift, as declared by the employer, is equal to only
30 minutes, it is reasonable to conclude that any employee performing only this action does not need to apply any personal means of protection.
UV protective gel curing machine for electronic industry
In case of this machine, the staff work is limited to collecting printed circuits once the protective gel is cured with UV radiation (Fig. 3). This machine has a UV radiator with the total power of 1.8 kW. According to information obtained from the em-ployer, one employee collects the ready printed circuits for the maximum period of 7 hours (25 200 seconds) per shift. Based on the measurement of effective irradiance with UV radiation, carried out in compliance with the method defined in the stan-dard PN-EN 14255-1: 2010 [6], using a radiometer, it was found that:
the NDN value at the work post for collecting ready printed circuits was exceeded by 78%, since the effective irradiance value of N = 53 J/m2 was obtained;
at the housing of a robot at the distance of 3.5 m from the UV source (the area of communication zone), with the irradiation of N = 21.2 J/m2.
Table 5. Measurement results of the effective irradiance for UV radiation at the inspector post Tabela 5. Wyniki pomiarów skutecznego natężenia napromienienia promieniowaniem UV
Activity body part Exposed radiation source [m] Distance from exposure time [s] Average
Irradiation [J/m2] Obtained from conducted
measurements Obtained from conducted measurements Position Controller – cup loading bay – front of the machine
30 Eyes 0.951.30 21 600 6.97·10–3 150.60 Face 0.951.30 7.15 10–3 154.44 Hands 0.200.50 14.72·10–3 317.95
Position Controller – cup lid loading bay – rear of the machine Eyes 0.50
1 800
3.82·10–3 6.88
Face 0.50 1.41·10–3 2.54
Hands 0.10.30 0.24·10–3 0.43
Table 6. Determined maximum exposure times Tabela 6. Wyznaczone dopuszczalne czasy ekspozycji
Activity body part Exposed effective Average irradiance
The highest acceptable value of effective
irradiation
The determined acceptable exposure time (without using any personal
means of protection) Cup loading bay –
front of the machine
eyes 6.97·10–3 30 72
face 7.15 10–3 30 70
hands 14.72·10–3 30 34
Cup lid loading bay – rear of the machine
eyes 3.82·10–3 30 131
face 1.41·10–3 30 355
Machines emitting infra-red radiation
Domestic Glass Glass-Works
Figure 4a shows a fragment of a glass-producing machine type 2C (10 sections, 3 drops of molten glass, colour-less glass, temperature of molten glass at 550C), used to manufacture jars (h = 0.125 m, = 0.07 m). During the normal operating condi-tions, an employee supervises visually the process of jar formation. Such a person is then located ap-proximately between 1 and 2.5 m from hot molten glass.
Figure 4b shows the bottle formation super-vision post, where bottles are made from orange glass (molten glass at 600C, the size of the manu-factured bottles h = 0.27 m, max = 0.07 m) using the glass manufacturing machine type 4D (10 sec-tions, 3 drops of molten glass). Figure 5a and 5b show a person during maintenance activities
(regu-Fig. 3. General view on the UV gel curing machine, from the side used to collect printed circuits; source: author’s photo-graph
Rys. 3. Widok urządzenia do utwardzania UV żelu ochronnego od strony odbierania obwodów drukowanych; źródło: fot. autor
a) b)
Fig. 4. Views of a fragment of the glass manufacturing machine: a) type 2C, b) type 4D – the bottle formation supervision post at the glass; source: author’s photograph
Rys. 4. Widoki fragmentów automatów szklarskich a) typ 2C, b) typ 4D – stanowisko nadzoru procesu formowania butelek; źródło: fot. autor
a) b)
Fig. 5. Adjustment activities on a glass manufacturing machine: a) type 2C, b) type 3A; source: author’s photograph Rys. 5. Prace regulacyjne na automacie szklarskim: a) typu 2C, b) typu 3A; źródło: fot. autor
lation and adjustment) of the glass manufacturing machine type 2C and type 3A. The latter one is used to manufacture colour-less bottles (tempera-ture of molten glass at 550C, the size of the manu-factured bottles h = 0.27 m, max = 0.07 m), where the glass manufacturing machine type 3A has 10 sections and uses 2 drops of molten glass. During these activities, such a person is located approxi-mately between 0.1 to 1 m from hot molten glass.
Conclusions
Based on the conducted measurement of infra-red irradiation levels at the examined work posts, an employee working at the glass manufacturing machine type 4D, 3A, 2C and 1B during the pro-cess of supervising product formation is not subject to any excess radiation above the NDN levels for infra-red radiation, hence not representing any thermal threat to eye cornea and lens. However, during any maintenance and repair works, related with adjustment of the glass manufacturing ma-chine type 2C and 3A, the NDN radiation levels for infra-red radiation were exceeded, hence creating thermal threat to eye cornea and lens.
Non-iron metal works
Figure 6 shows a work post of a furnace opera-tor in a non-iron metal works, when supervising the
Fig. 6. A work post for a furnace operator in a non-metal metal works – supervision of the proper course of the process of casting metal into a ladle; source: author’s photograph Rys. 6. Stanowisko wytapiacza metali nieżelaznych – nadzór nad prawidłowym przebiegiem odlewania metalu do kadzi; źródło: fot. autor
proper course of the process of casting metal into a ladle. During this process, such an employee is located between 0.8 to 1.2 m from molten metal with the typical temperature of 900C.
In this case, the NDN levels for infra-red radia-tion were substantially exceeded, hence creating thermal threat to eye cornea and lens.
a) b)
Fig. 7. A view of an example of SACK type printing frame (a), A view of the light source for printing frames, 8 kW, type Brillant (b) Rys. 7. Widok przykładowej kopioramy offsetowej typ SACK (a), widok źródła światła do kopioramy o mocy 8 kW – typ Brillant (b)
Devices emitting visible radiation – a printing frame
This device is used for contact printing, i.e. irra-diating the light-sensitive material through a plate (with the exposed image), placed directly on this material (apart from regular plates, various types of materials can be used, including e.g. carbon paper with an image etc.). In order to guarantee that the copying process is indeed correct, it is critical, that the plate is irradiated in such a way that the image bearing side enters into direct contact with the light-sensitive layer – otherwise, the obtained im-age can be slightly diffused. Professional printing frames are very complex devices, primarily because of the requirement to achieve uniform irradiation for the whole image area and the need to adjust the light quantity in a precise manner. Additionally, it is also necessary to remove any air between the plate and the target surface to avoid creation of the Newton rings. Figure 7a shows a printing frame equipped with a curtain to protect eyesight of an operator during the process of irradiation. The up-per part shows a lamp with the total power of 3 kW, while lower part shows a glass cover and a rubber desk to remove any air between the plate and the film. Typically, printing frames are equipped with light sources with the power of 0.5, 1, 2, 3, 4 or 8 kW (Fig. 7b).
Conclusions
The machine category represents the basis for evaluation of any threat caused by optical radiation emitted by the machine and to determine type of protection means needed to eliminate or diminish level of emitted radiation. For this reason, manufac-turers of machines emitting any type of radiation are obligated to determine the emission category. In case of new machines – prior to their introduc-tion to the market, and in case of already existing machines – at the customer site. However, the examined overview of machines indicates that none of them was attributed an emission class.
References
1. Dyrektywa 89/655/EWG z dnia 30 listopada 1989 r. dotycząca minimalnych wymagań w dziedzinie bezpie-czeństwa i higieny użytkowania sprzętu roboczego przez pracowników podczas pracy (druga dyrektywa szczegóło-wa w rozumieniu art. 16 ust. l dyrektywy 89/391/EWG). 2. PN-EN 12198-1+A1: 2009. Bezpieczeństwo maszyn.
Oce-na i zmniejszanie ryzyka wynikającego z promieniowania emitowanego przez maszyny. Część 1: Zasady ogólne. 3. PN-EN 12198-2+A1: 2009. Bezpieczeństwo maszyn.
Oce-na i zmniejszanie ryzyka wynikającego z promieniowania emitowanego przez maszyny. Część 2: Sposób pomiaru emitowanego promieniowania.
4. PN-EN 12198-3+A1: 2009. Bezpieczeństwo maszyn. Oce-na i zmniejszanie ryzyka wynikającego z promieniowania emitowanego przez maszyny. Część 3: Zmniejszenie pro-mieniowania przez tłumienie lub ekranowanie.
5. Dyrektywa 2006/42/WE Parlamentu Europejskiego i Rady z dnia 17 maja 2006 r. w sprawie maszyn, zmieniająca dy-rektywę 95/16/WE.
6. PN-EN 14255-1: 2010. Pomiar i ocena ekspozycji osób na niespójne promieniowanie optyczne. Część 1: Promienio-wanie nadfioletowe emitowane przez źródła sztuczne na stanowisku pracy.
7. Rozporządzeniem Ministra Pracy i Polityki Społecznej z dnia 29 lipca 2010 r. zmieniającym rozporządzenie w sprawie najwyższych dopuszczalnych stężeń i natężeń czynników szkodliwych dla zdrowia w środowisku pracy (Dz.U. z 2010 nr 141 poz. 950).
This paper has been prepared on the basis of the results of a research task carried out within the scope of the second stage of the National Programme “Improvement of safety and working conditions” supported in 2011–2013 – within the scope of state services and statutory activity – by the Ministry of Labour and Social Policy. The Central Institute for Labour Protection – Na-tional Research Institute is the Programme’s main co-ordinator.
Recenzent: dr hab. inż. Zbigniew Matuszak, prof. AM Akademia Morska w Szczecinie
