Maritime University of Szczecin
Akademia Morska w Szczecinie
2010, 24(96) pp. 74–79 2010, 24(96) s. 74–79
Evaluation of professional hazards related with optical
radiation for ship’s hull welders at temporary work posts
Ocena zagrożenia spawaczy kadłubowych promieniowaniem
optycznym na tymczasowych stanowiskach pracy
Andrzej Pawlak
Central Institute of 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: non-laser optical radiation, ultra-violet, visible and infra-red radiation Abstract
In this paper, we examine sources of optical radiation and the effects of interaction of specific types of optical radiation i.e. ultra-violet, visible and infra-red, on a human organism. Next, the current criteria for assessing optical radiation hazards and contemporary measurement methods for establishing the total and effective intensity of irradiation with ultra-violet radiation, as well as the intensity of irradiation with infra-red and visible radiation. In the following section, examples of temporary working posts for welders were presented, as used during maintenance works aboard ships. Measurement results for optical radiation at the selected working post were then quoted, accounting for three specific exposure times. The last section contains conclusions drawn from measurement results and interviews with a group of ship hull welders.
Słowa kluczowe: nielaserowe promieniowanie optyczne, promieniowanie ultrafioletowe, widzialne i
pod-czerwone
Abstrakt
W referacie omówiono źródła promieniowania optycznego oraz skutki oddziaływania poszczególnych rodza-jów promieniowania, tj. ultrafioletowego, widzialnego i podczerwonego na organizm człowieka. Przedsta-wiono aktualne kryteria oceny zagrożenia promieniowaniem optycznym oraz metody pomiarów całkowitego oraz skutecznego natężenia napromienienia promieniowaniem UV oraz natężenia napromienienia promie-niowaniem podczerwonym i widzialnym. W dalszej części pokazano przykładowe, tymczasowe stanowiska pracy spawaczy podczas wykonywanych prac remontowych na pokładzie statku. Przytoczono wyniki pomia-rów promieniowania optycznego na wybranym stanowisku pracy z uwzględnieniem trzech różnych czasów ekspozycji. Zamieszczono wnioski z wyników pomiarów oraz z rozmów z grupą spawaczy kadłubowych.
Introduction
Optical radiation comprises part of the electro-magnetic radiation spectrum with the wavelengths spanning 100 nm – 1 mm. Optical radiation com-prises three primary classes i.e. ultra-violet (UV), visible (VIS) and infra-red (IR) radiation. Typi-cally, the infra-red and ultra-violet ranges are fur-ther subdivided into bands: A (close), B (average) and C (distant). According to the standard PN-90/E-01005 [1], the said bands for ultra-violet
radiation range occupy the following wavelength ranges:
UV-A 315 – 400 nm UV-B 280 – 315 nm UV-C 100 – 280 nm.
Wavelengths shorter than 200 nm are typically not observed at work places, since they are highly attenuated by air. In case of infra-red radiation, individual bands occupy the following wavelength ranges [1]:
IR-A 780 – 1400 nm IR-B 1400 – 3000 nm IR-C 3000 nm – 1 mm.
Sources of optical radiation
Sources of optical radiation can be divided into the following classes:
natural sources (the Sun, sky, the Moon etc.), electrical sources (UV radiators, IR radiators,
light bulbs, fluorescent lamps, medium- and high-pressure mercury lamps, metal halogen lamps, xenon lamps, deuter lamps etc.),
technological sources (processes) (welding, steelwork furnaces, heating processes etc.). Artificial sources of optical radiation include both electrical sources as well as technological processes.
Light sources can be also divided into thermal and luminescent classes.
Thermal sources
Radiation of thermal sources, commonly referred to as thermal or temperature radiation, can be described with high precision using the perfect black body radiation principles (PBB): Planck, Wien and Stefan-Boltzmann equations. The afore-mentioned principles indicate that a body with the temperature below 500 K generates infra-red radiation with the wavelength no exceeding 2 µm. Bodies with temperature ranging between 1000 K and 1800 K radiate additionally close infra-red radiation (IR-A) and very little visible radiation (below 1%). Only when the temperature threshold of 3000 K is exceeded, bodies emit infra-red and visible radiation, together with approximately 0.1% of ultra-violet radiation [2]. Typical thermal radia-tion sources include:
holes and walls of melting, heating, hardening, ceramic and glass furnaces;
molten metal or glass;
metal or glass elements heated to high tempera-ture, subject to plastic processing, hardened or formed;
lamp infra-red radiators used in textile industry to e.g. drying yarn, in animal breeding farms to warm up animals, in agriculture to dry to-bacco, baking grain and in the plastic processing industry;
furnaces, heaters: steam, electric, coal-fired or gas-fired.
Luminescent sources
Luminescent radiation sources are of much higher efficiency than thermal sources. Their
radia-tion is not subject to PBB principles. The most commonly luminescent radiation sources include: medium- and high-pressure mercury lamps, welding arcs,
plasma and gas torches,
ultra-violet radiators of “artificial sun” and “black light” type (a Wood’s lamp, the glass bulb of which is covered with black lumino-phore).
Welding arcs and torches represent a very spe-cific type of optical radiation sources. Their radia-tion is comprised of intensive thermal radiaradia-tion of welding gases, welded or cut elements, electrode and fusing agents, heated to very high temperature, the spectrum of which is overlaid with lines and bands of radiation characteristic for these materials. The temperature of a gas torch burner does not typically exceed 2000 K, hence its radiation is pri-marily comprised of infra-red and visible radiation. Only hydrogen and acetylene torches, taking advan-tage of much higher burning temperature, can emit close ultra-violet radiation. On the other hand, tem-perature achievable in electric and plasma arcs, exceeds 4000 K, and when the welding process is carried out in a neutral gas shield – the temperature can reach even 30 000 K. Such devices emit inten-sive blue and ultra-violet radiation, including also short-wavelength ultra-violet light. From all the ultra-violet radiation sources, electric arcs represent the most severe health hazard [2].
Effects of influence of optical radiation on a human organism
Optical radiation is a crucial environmental factor indispensable for proper development and activity of humans. However, excessive optical radiation causes multiple adverse biological effects, leading to eye or skin damage. Effects of exposure to excessive radiation depend on its physical parameters, absorbed radiation quanta as well as optical and biological properties of the exposed tissue [2].
Effects of ultra-violet radiation
Effects of ultra-violet radiation are primarily photo-chemical, while biological effects of this particular radiation depend on the absorbed quanta, wavelength and type of exposed tissues. Two pri-mary types of harmful effects of ultra-violet radia-tion on a human organism can be distinguished: skin effects and eye effects.
Ultra-violet radiation absorbed by skin can cause a number of harmful photo-chemical reac-tions, e.g. skin erythema, pre-tumour and tumour
changes, increase in skin pigmentation, flaking of epidermis, though there are also some beneficial effects e.g. increase in organism immunity level, creation of D3 vitamin, decrease in the overall cholesterol levels, faster wound healing, improve-ment in infection conditions and some skin diseases [2]. The most visible, most common and most frequently examined effect of skin exposure to ultra-violet radiation is skin erythema. Once skin erythema passes away, increased pigmentation follows (referred to as sun tan), which plays a protective role against harmful ultra-violet radiation. When though repeated exposure of skin to ultra-violet radiation increases its immunity, however, prolonged exposure to high levels of ultra-violet radiation results in adverse changes in epidermis: speeds up the skin ageing process and causes tumour changes.
Ultra-violet radiation absorbed through eyes can cause cornea and conjunctiva inflammations, damage to retina and cornea as well as occurrence of photo-chemical cataract. Cornea and conjunctiva inflammations are the most common and severe effect of exposing eyes to ultra-violet radiation. Cornea inflammation typically manifests itself with photo-phobia, increases lacrimation, sensation of a presence of an alien body (“sand”) in the eye, eyelid spasms and sometimes even eyesight impair-ment. On the other hand, conjunctiva inflam-mations caused by ultra-violet radiation manifest themselves with reddening, itching, irritation, lacrimation, sometimes also with photo-phobia and in case of higher absorbed dosage, it is also possible to have pain and even eyesight impairment [2]. Ultra-violet radiation with the wavelengths exceeding 300 nm, reaching the eye lens, is highly absorbed and may cause local occurrence of cataracts, i.e. local lens opacity. Cataracts develop slowly and their evolution takes typically years.
Effects of visible radiation
In case of visible radiation, any harmful effects are limited to human eyes. Intensive visible radia-tion, especially the so-called blue light, with the wavelength ranging 400 – 500 nm, may cause ther-mal or photo-chemical damage and impairments to the eye retina [2]. Such radiation is typically generated during technological processes, such as e.g. welding. It is also the primary component of solar radiation reaching the Earth. In practise, eye retina is damaged due to photo-chemical reaction caused by overlapping effects of exposure throughout the day-long hazard period. On the other hand, thermal retina damage caused by
industrial radiation sources is infrequent; primarily because of the natural defensive reflect of the eye against high intensity light sources.
Effects of infra-red radiation
Effects of infra-red radiation on a human orga-nism are primarily limited to thermal effects, which results in the increase in temperature of the exposed tissue and neighbouring tissues, and sometimes also the whole organism. It is considered that the effects of infra-red radiation exposure depend primarily on the radiation intensity and much less on the expo-sure time and wavelength [2]. This type of radia-tion, after exceeding a certain level of intensity, may cause skin burns as well as such eye diseases as cataracts, choroid or retina degeneration, in-cluded in the group of professional diseases. The most severe illness related with exposure of an eye to excessive levels of infra-red radiation is the so-called infra-red cataract (also referred to as steel mill cataract) or alternatively lens opacity.
It is also necessary to remember that just like in case of ultra-violet radiation, infra-red radiation may also have beneficial impact on a human orga-nism and it is used for therapeutic purposes.
Criteria of optical radiation related hazard evaluation process
According to the decree of the Minister of Labour and Social Politics from the 29th of Novem-ber 2002 on the highest admissible intensity and concentration levels for health hazardous agents in work places [3], the following levels of NDN are in force, applicable to the examined work places:
Ultra-violet radiation
The highest admissible effective irradiation intensity for eyes and skin during a one day’s long worth of work time, irrelative of its duration, is equal to 30 J/m2. The curve of relative biological effectiveness of ultra-violet radiation S() is de-fined in the Polish Standard number PN-T-06589: 2002 [4].
Visible radiation
The highest admissible effective intensity value for eyes with the exposition times above 10 000 seconds, with the radiation source size below 11 mrad is equal to 1 W/cm2. The curve of relative spectral effectiveness of a photo-chemical retina damage B() is defined in the Polish Standard number PN-T-05687: 2002 [5].
Infra-red radiation
Total irradiation intensity with infra-red radia-tion for eyes – Ec for one-time exposition time ti shorter than 1000 seconds should not exceed the value calculated using the following equation:
Ec 18 000 ti–3/4 (1)
Measurement method
Measurement of the total and effective irradia-tion intensity with ultra-violet radiairradia-tion as well as attenuation coefficients for commonly used means of personal protection were carried out according to the standard PN-T-06589: 2002 [4]. On the other hand, measurement of the total and effective irra-diation intensity with infra-red and visible rairra-diation
as well as attenuation coefficients for commonly used means of personal protection were carried out according to the standard PN-T-06587:2002 [5]. The aforementioned measurements were carried out using the radiometer type IL 1800 (manufactured by International Light – USA) with the measure-ment probes type SED 340/ACT5 (evaluation of eye and skin hazard for ultra-violet radiation), SED 033 TBLU/SCS 395/R (evaluation of photo- -chemical hazards for eye retina for visible light) and SED 623/SCS780/W (evaluation of thermal hazards for eyes for visible radiation).
Description of the study object
The examined welding works were carried out during the maintenance works inside of the ship depicted in figures 1 and 2.
Fig. 1. Examples of locations where welding works were carried out (the photo taken by the author) Rys. 1. Przykładowe miejsca wykonywania prac spawalniczych (fot. autor)
Fig. 2. Examples of welding posts located inside of the ship (the photo taken by the author)
Rys. 2. Przykładowe stanowiska spawal-nicze znajdujące się wewnątrz statku (fot. autor)
A temporary welding post located on the top deck and a cart with a very large quantity of coiled gas feeding lines, connecting gas bottles with the torch, are presented in figure 3.
Fig. 3. A temporary welding post and a cart with gas feeding lines (the photo taken by the author)
Rys. 3. Tymczasowe stanowisko spawalnicze oraz wózek z przewodami (fot. autor)
Fig. 4. A view on the bottom of a ship's hull when removing fragments of bent metal sheets (the photo taken by the author) Rys. 4. Widok dna statku podczas wycinania fragmentów pogiętej blachy (fot. autor)
The figure 4 presents the bottom of a ship’s hull from the level of the dry dock, when cutting out fragments of the ship’s skin using a gas torch (removing fragments of bent metal sheets).
Figure 5 presents welding work posts located at the dry dock level, when executing repair works on the ship skin.
Fig. 5. Welding work posts located at the bottom of a ship’s hull (the photo taken by the author)
Rys. 5. Spawalnicze stanowiska pracy znajdujące się w dnie statku (fot. autor)
Measurement results
Results of the optical radiation measurements are presented for the most disadvantageous condi-tions of gas welders’ work – when executing repair works on the ship's skin. The welding in this case was done by hand, in a standing position. The measurement points during the welding process were located at the welder’s hands and head. The distance between the eyes and face and the executed weld was equal to 0.5 m and between the hands and the weld – 0.08 m. Table 1 presents results of the effective irradiation with ultra-violet radiation for the adopted total exposition times: 3, 5 and 6 hours.
Table 1. Result of the welder’s exposure to ultra-violet radia-tion
Tabela 1. Wyniki narażenia spawaczy na promieniowanie ultrafioletowe Irradiated body part Total expo-sition time [s] Irradiation intensity [W/m2] Effective irradiation [J/m2] NDN Irradiation [J/m2] eyes 10 800 0.00139 15.00 30 face skin 0.00219 23.65 hands 0.00330 35.64 eyes 18 000 0.00139 25.02 face skin 0.00219 39.42 hands 0.00330 59.40 eyes 21 600 0.00139 30.02 face skin 0.00219 47.30 hands 0.00330 71.28
Table 2 presents results of the effective irradia-tion with visible radiairradia-tion taking into considerairradia-tion that the total exposition time exceeds 10 000 se-conds.
Table 2. Result of the welder’s exposure to visible radiation Tabela 2. Wyniki narażenia spawaczy na promieniowanie widzialne Irradiated body part Total expo-sition time [s] Irradiation intensity [W/cm2] NDN Irradiation intensity [W/cm2] eyes > 10 000 0.51 1
Table 3 presents results of the effective irradia-tion with infra-red radiairradia-tion for the adopted single-time exposition single-times equal to 35 seconds and 300 seconds.
Table 3. Result of the welder’s exposure to infra-red radiation Tabela 3. Wyniki narażenia spawaczy na promieniowanie podczerwone Irradiated body part Total exposi-tion time [s] Irradiation intensity [W/m2] NDN Irradiation intensity [W/m2] eyes 35 191 1251 eyes 300 191 250
The calculated attenuation coefficients T for the commonly used welding shield for specific optical radiation bands were equal to:
for ultra-violet radiation: T = 269∙103, for infra-red radiation: T = 21, for visible radiation: T = 6∙103.
Conclusions
Based on the conducted measurements of ultra- -violet radiation for the exposition time declared by the contractor during a single work day’s worth of work time equal to at least 3 hours, potential hazard to hand skin was confirmed when using gas welding technique. When the work time increases to 5 hours, there is additional hazard to face skin, while when the work time increases to 6 hours – there is also eye hazard.
Based on the conducted visible radiation measurements, it was concluded that there is no threat to eye retina when performing gas welding.
Results of the infra-red radiation measurements for the adopted single exposition times do not pro-vide any indication of occurrence of any potential hazards related with this radiation when performing gas welding.
Due to the occurrence of high professional hazard at such work places, it is necessary to employ protective gloves and welder’s helmets
throughout the whole work time. Based on the determined ultra-violet radiation attenuation coeffi-cients for the welder’s helmet used when welding, it was concluded that it diminishes the professional hazards to a low level. Due to potential hazard to hand skin resulting from ultra-violet radiation, when performing gas welding it is recommended for employees to use protective gloves on both hands.
Detailed conclusions
The following conclusions were elaborated based on interviews with a group of 30 ship’s hull welders:
• eyesight ailments like: irritation, itching, pre-sence of alien bodies, heavy eyelids, redness are observed especially after night shifts;
• noticeably increased tiredness, especially for eyesight, was reported with work shifts exceed-ing 8 hours;
• eyesight ailments like: irritation, itching, lacri-mation and generic eye pain, preventing welders from closing their eyes or even sleep were reported primarily after a work shift when eyes were exposed to direct torch arc – especially electric arc – from neighbouring work posts; • work conditions on the production hall were
reported to be much worse, primarily because of the lack of welding screens, where many welders work in proximity – arcs are reflected from walls, there is increased noise level and higher dustiness;
• welders reported also strong stench when heat-ing up metal sheets;
• additionally, too many employees work in small, confined spaces e.g. in tanks – an assembler, a welder and a grinder.
References
1. PN-90/E-01005. Lighting technique. Terminology. 2. WOLSKA A., PAWLAK A.: Non-laser optical radiation.
Evaluation of professional hazards. Principles of metho-dology. CIOP-PIB, Warsaw 2004, 181–193.
3. Decree of the Minister of Labour and Social Politics from the 29th of November 2002 on the highest admissible
inten-sity and concentration levels for health hazardous agents in work places. Legislation Journal 2002, 217, 1833.
4. PN-T-06589: 2002. Protection against optical radiation. Measurement methods for ultra-violet radiation at work places.
5. PN-T-06587: 2002. Protection against infra-red radiation. Measurement methods for visible and infra-red radiation at work places.
Recenzent: dr hab. inż. Zbigniew Matuszak, prof. AM Akademia Morska w Szczecinie
