FUNDACIÓN MAPFRESeguridad y Medio Ambiente

Year 31 Nº 124 2011

Occupational risk prevention for workers using oxyacetylene torchesINDUSTRIAL HYGIENE

In the working world there are some especially high-risk professions involving potentially retina-damaging welding processes. Those most at risk are car workers, metalworkers and installers of air conditioning and heating systems. Although firms are bound under current legislation to equip their workers with the necessary protection against any harmful welding-torch radiation, the welders themselves often choose not to wear this protection because the overdark lenses balk their vision and make them prone to accidental burns or other working errors. They therefore prefer to weld without wearing any protection at all. This renders them liable to irreversible retina damage, including even absolute scotomas of serious consequences. This study proposes new protective filters that ensure both retina photoprotection and proper visibility of the working area. An analysis was first made of the torch’s emission spectrum and the necessary filters were then designed to absorb the harmful bands. This led to the development of a prototype. Several aspects of visual perception were then assessed using this new filter proposed by the Universidad Complutense de Madrid (UCM) and another conventional welding filter. The results show that the UCM filter acts as an optimum protection lens for oxyacetylene welding and it is therefore put forward as a benchmark filter for type approval by the competent authorities.

AUTHORS: CRISTINA BONNIN-ARIAS, EVA CHAMORRO-GUTIÉRREZ, GUILLERMO RAMÍREZ-MERCADO, LUIS-LUCIO LOBATO-RINCÓN, JUAN JOSÉ NAVARRO VALS and CELIA SÁNCHEZ-RAMOS.


Before going into the subject of this paper proper we first have to look at certain basic concepts bound up with light and other radiation. The electromagnetic spectrum is a continuum of all electromagnetic waves, ranging from the shortest-wave radiation at one end, such as gamma rays and X rays, to the longest wavelengths like radio waves at the other end, passing on the way through the visible spectrum of ultraviolet to infrared. Visible light is the name given to this range of the electromagnetic spectrum that is visible to the human eye, from 380nm (at the shortest end) to 780nm (at the longest end). Hard by the 380 nm end lies the ultraviolet and hard by the 780nm end lies the infrared (figure 1).




Figure 1. Electromagnetic radiation, broken down by wavelength spectrums.

The electromagnetic energy of a wave with a given wavelength λ(in a vacuum) has an associated frequency and photon energy. High frequency electromagnetic waves, therefore, have a short wavelength and high energy, while low frequency waves have long wavelengths and low energy (figures 2 and 3).


Figure 2. Graph showing the difference between long- and shortwave radiation.


Figure 3. Wavelengths of three different types of radiation.

Back in 1966 Noell had already shown that ultraviolet and blue light (shortest wavelengths of the visible spectrum) have an adverse affect on eyes (retina). This is because of the very fact explained in the above paragraph: that this shortwave radiation has higher energy than longer wavelength radiation. Retinal light toxicity has been traditionally broken down into three types: photomechanical (effects of the collision of the lightwaves), photothermal (local heat produced by the waves) and photochemical (changes in macromolecules). Light-induced retina changes are pretty well understood nowadays (Wenzel, 2005; Wu, 2006). From all the above it follows that light, albeit a sin qua non for vision, is liable to damage parts of the visual system upon tissue absorption. The portion of energy absorbed by any tissue depends on the latter’s incident radiation transparency; this is a crucial factor for determining the types of photobiological effects that might be induced. The mechanical action arises basically from the rapid, shockwave-generating impact of energy on the melanosomes of the retina pigment epithelium. These shockwaves cause an irreparable damage to the photoreceptors and the retina pigment epithelium, called photomechanical damage.

The harmful effect on the tissue might arise when mechanical compressive or tensile forces form microcavitation bubbles that are lethal not only to the retina pigment epithelium but also to other cells. The effect is caused by high irradiation (in the megawatt / cm2 range) and short periods of exposure (in the nanosecond to picosecond range) during which the energy is absorbed so quickly by the melanin granules in the retina pigment epithelium that heat dispersion has no time to occur.

A definition should also be made of photothermal damage. A quantum of radiant energy (a photon) can be absorbed by a molecule only if the photon energy fits the energy difference between the molecule’s normal energy level and the maximum permitted energy level. The rotational and vibrational states of the molecule quanta override the excitation states caused by the longest wavelengths in the «visible» spectrum and in near infrared (700-1400nm). The energy vibration gained by the molecule is rapidly dissipated in collisions with other molecules, momentaneously raising the local level of the kinetic energy itself; this process is seen as a rise in temperature. Thermal lesions are not caused by the increase in kinetic energy until the irradiance is high enough to boost the temperature by at least 10ºC above the retina’s ambient level. The thermal reaction hence depends on the irradiance thresholds. Thermal damage is much worse in the centre of the lesion where the temperature increase is higher.

Lastly, photochemical damage, as a different form of interaction between radiant energy and biological molecules, occurs when incident radiation has a wavelength in the high energy portion of the «visible» spectrum. An electron in an excited state might revert to its ground state by dissipating the extra energy, breaking up another molecule by means of a direct electron- or hydrogen-exchange, producing reactive oxygen species. The process might also produce other free radicals that play an important role in tissue damage (Margrain et al., 2004). No acute damage occurs below a certain irradiance threshold.

After this introduction we can now home in on the particular theme of this article: welding. The American Welding Society (AWS) defines welding as “a joining process that produces coalescence of metals (or thermoplastic materials) by heating them to the required welding temperature, with or without application of pressure and with or without the use of filler metal”. In less technical terms welding occurs when the separate pieces of metal are joined into a single piece upon being heated up to the fusion temperature (Jeffus, 2009). Welding can be broken down into two basic types: autogenous and heterogeneous; as the names suggest, in the first case the filler metal is the same as the parent metal; in the second case, different. Depending on the energy input for the join, welding can also be categorised as fusion welding (with heat input) or pressure welding or a combination of both; these involve the use of different welding devices. This study centres on oxyacetylene gas welding (figure 4).



Figure 4. Breakdown of the different welding types.

Gas welding generates heat when an oxygen mixture burns with a given gas, frequently acetylene (C2H2), in a blowtorch nozzle. The input heat in this type of welding stems from the burning reaction, which is strongly exothermic, building up to temperatures of about 3500º C. (Molera Solá, 1992). There are also other types of welding devices such as the electric arc or plasma arc; the latter generates heat in the range of 10,000 to 30,000º C. This energy emission might be harmful to the human body and cause more ocular complications than conventional arc welding techniques (Choi et al., 2006) (figures 5a and 5b).

ACCORDING TO THE NATIONAL STATISTICS INSTITUTE (INSTITUTO NACIONAL DE ESTADÍSTICA), IN 2004 1,200,000 PEOPLE IN SPAIN WERE WORKING IN THE SECTORS MOST EXPOSED TO WELDING TORCHES

Bearing in mind all the information set out above, and within the context of occupational risks, there are some professions, such as welders, that are especially prone to light toxicity due to a combination of photothermal, photomechanical and photochemical factors. In general people exposed to phototoxicity will develop an occupational disability, absolute in 90% of the cases, with the concomitant harm to them and damage to society as a whole. Pathologies of this type are irreversible; the most frequent are detached retina, macular holes and photofobia.

This occurs because the high temperature flame irradiated during the welding process emits a broad series of electromagnetic waves (ultraviolet, short wavelengths of the visible spectrum and infrared), which are liable to cause eye damage due to the energy transmitted (Choi et al., 2006). Ultraviolet B (UVB) and ultraviolet C (UVC) radiation can cause photokeratitis and photoconjunctivitis, whose typical symptoms are intense pain, eyewatering, sandiness, photophobia, etc. These affects are acute but reversible. The visible radiation or light might produce thermal and/or photochemical retina lesions with total or partial vision loss (acute affects that might be irreversible). Repeated exposure to infrared (IR) radiation might produce cataracts of thermal origin, due to the high temperatures (chronic and irreversible effects). The number of people exposed during many hours of the day to damaging blowtorch light is very high. The most affected professions, precisely due to the exposure time, are construction workers and metalworkers as well as air-conditioning and heating installers. According to the National Statistics Institute (Instituto Nacional de Estadística: INE), the number of people working in this sector in Spain added up to 1,200,000 in 2004 (MCA-UGT).

Current legislation obliges the firm to equip its blowtorch-using workers with protection against violet-blue radiation. Although goggles and face shields are available for workers most of them are not taken up. The main reason for this is the excessive darkening of the lenses in the conventional face shields, which absorb not only the harmful bands but also 99% of the whole visible spectrum. The welders therefore complain that, when wearing the conventional welding goggles, their vision is almost nil, exponentially increasing the risk of burns (Kim, 2007). (figure 6). The graph in figure 7 shows the absorption curves of the conventional welding filters, of which the least absorbent version transmits only 1% of the visible spectrum.


Figure 6. Difference of the image when looking through the welding filter proposed herein (left image) and the traditional welding filter (right image).


Figure 7. Absorbance curves of conventional welding filters. This graph shows the highest absorbing filter (red line) and the lowest absorbing filter (black).

The objective of this study is therefore to design a new welding filter that provides the same level of protection as a conventional welding filter but also ensures good vision of the working area.

MATERIALS AND METHOD

In this study an assessment was made of 36 people of both sexes, 22 men and 14 women, of working age. The mean sample age was 44±14 years. The absorbance readings were taken with two different spectrometers: the Spectrapro-750 (SOPRA), for measuring the flame emission spectrum of the oxyacetylene torch and the Humphey Lens Analyzer 350 (Zeiss Humphrey Systems), for assessing the filters. Different types of optical filter were also used: firstly, selective absorbance filters for wavelengths ranging from 380 to 500nm were used for designing the new UCM protective filter, to determine the required absorbance for the new protection device against the oxyacetylene blowtorch emission. Subsequently to evaluate the various visual function aspects, the newly designed filter was used together with a conventional type-approved protective filter, currently available for welders (figure 8).


Figure 8. Spectral absorbance curves of the filters used in this study. Black line: conventional filter. Green line: filter proposed by UCM.

Other concomitant factors assessed were visual acuity, contrast sensitivity, colour discrimination and stereoacuity. To evaluate these aspects of visual function we used the tests normally employed for assessments of this type, according to manufacturer’s instructions, in near vision and under photopic lighting conditions. Specifically, the following tests were used to evaluate each aspect: for visual acuity the Traditional Runge Pocket Near Vision Card (Precision Vision, USA) (figure 9); for contrast sensitivity, the VCTS test (Vistech Consultans, INC, 1988, Stereo Optical Company) (figure 10); for colour discrimination, the Farnsworth-Munsell D-28 HUE test (figure 11), and, finally, for stereoacuity, the Titmus test (figure 12).

All the evaluations were made in binocular form. The subjects were examined under normal working conditions, i.e., with the vision-correcting lenses used for carrying out near-vision work regardless of whether these lenses were visually optimal. Each one of the visual function parameters was assessed under three conditions: 1) without any protection filters, 2) using a conventional welding filter, and 3) using the protection filter proposed by the Universidad Complutense de Madrid (UCM). The test order and the use or non-use of filters was random.

The Statgraphics Plus5.0 Professional Edition software was used for comparative statistics to ascertain the effects of the filters on the various visual function readings. All the comparisons were made assuming an alpha error of 0.05.

RESULTS

Readings of the blowtorch emission spectrum with and without the X-450 filter

A graphic illustration is given below of the emission spectrum of an oxyacetylene torch in the wavelength range from 380nm to 750nm. Figure 13a shows that the torch emission is relatively stable, albeit with some differences between the three curves presented therein (figure 13a).

Graph 13b shows the spectrum emission of the oxyacetylene torch without any filter (red line) and the emission of the same torch but this time using the filter X-450 (green line). The reading taken with X-450 shows that transmittance 0 (in relative units) is obtained for short wavelengths ranging from 400 and 450 nm while allowing through the other wavelengths (of the visible spectrum); this ensures proper vision of the working area (figure 13b).


Figure 13a. Emission curves of the oxyacetylene torch in the wavelength range 380nm to 750nm, without filters, taken three times (after turning off and restarting the torch).


Figure 13b. Emission curves of the oxyacetylene torch (red line) and the same oxyacetylene torch but this time with the optical filter absorbing phototoxic wavelengths (green line). The reading labelled «torch 2» in figure 14 was used for this comparative graph.

RETINA DAMAGE FROM WELDING-TORCH RADIATION IS BOTH ACUTE AND CHRONIC SINCE THE ACUTE EXPOSURE TO INTENSE LIGHT OCCURS ON AND OFF THROUGHOUT THE WORKER’S WHOLE WORKING LIFE

Descriptive and comparative results of visual acuity

A comparison of the different protective filters shows that the UCM-proposed filter does not cause significant changes in the near visual acuity readings (table 1 and figure 14). With the conventional filter, on the other hand, there is a significant reduction in the near visual acuity readings (table 2 and figure 14).

Table 1. Near visual acuity readings with/without the UCM-proposed protective filter, expressed on logMAR scale
AV Without filter Conventional filter Differences p-value
LogMAR scale 0.1 ± 0.22 0.13 ± 0.22 -0.03 ± 0.07 0.999994
Table 2. Near visual acuity readings with/without the conventional protective filter, expressed on logMAR scale
AV Without filter Conventional filter Differences p-value
LogMAR scale 0.1 ± 0.22 0.49 ± 0.06 -0.4 ± 0.18 2.04E-07*

Descriptive and comparative results of stereoacuity

No statistically significant differences were observed in stereoptic vision readings using the UCM-proposed filter by comparison with the stereoacuity readings obtained without the filter. Nonetheless a comparison of depth perception without any filter and with the conventional filter shows low depth discrimination in the latter case with statistically significant differences (table 3 and figure 15).

Table 3. Stereoacuity readings with/without protective filters: conventional filter vs filter proposed by UCM
Without filter (arc “) Filter (arc “) Differences (arc “) p-value
UCM filter 97 ± 95 89 ± 78 8,5 ± 40 0.999994
Conventional filter 97 ± 95 279 ± 531 -184 ± 470 2.11E-05

Descriptive and comparative results of colour discrimination

This aspect of visual function was ascertained by the number of hue-ordering errors made in the FM test. Table 4 shows that both filters reduce colour discrimination. A comparison of these readings against non-filter readings shows statistically significant differences. For a clearer display of the results, the data have been transformed into error percentages in figure 16 and in table 5.

Table 4. Number of hue-ordering errors in the Farnsworth-Munsell test with/without welding filters: conventional filter vs UCM-proposed filter.
No. of Errors Without filter Filter Difference p-value
UCM filter 5 ± 4 6 ± 4 1 ± 3 0,006 *
Conventional filter 5 ± 4 17 ± 3 12 ± 5 0 *
Table 5. Percentage of hue-ordering errors in the Farnsworth-Munsell test with/without welding filters: conventional filter vs UCM-proposed filter.
% Errors Without filter Filter Difference
AG5 filter 18 24 5
AG45 filter 18 61 43

The difference column clearly shows that the hue-ordering error percentage is very high with the traditional filter, about 43%. With the UCM-proposed filter, however, the loss of colour discrimination is only 5%. To ensure correct carrying out of this test it is crucial to explain the methodology properly beforehand. The first step in our procedure was always to carry out the non-filter assessment of colour perception, to ensure a good learning phase. The subsequent tests with filter were then conducted in random order.

Descriptive and comparative results of contrast sensitivity

When using the UCM-proposed filter there was a statistically significant reduction in near vision contrast sensitivity readings for spatial frequencies 6 cpd and 18 cpd. When using the conventional filter, however, there was a greater loss in near vision contrast sensitivity for all spatial frequencies. The differences between the UCM filter and the conventional filter were significant at all spatial frequencies (table 6).

Table 6. Statistical significance of near vision contrast sensitivity with/without the UCM-proposed filter and conventional filter.
Spatial Frequency P-value without filter vs. UCM filter P-value without filter vs. conventional filter P-value UCM filter vs. conventional filter
1,5cpg 0,999 0,000 * 0,000 *
3cpg 0,417 0,000 * 0,000 *
6cpg 0,028 * 0,000 * 0,000 *
12cpg 0,316 0,000 * 0,000 *
18cpg 0,022 * 0,000 * 0,000 *

A comparison of the readings obtained with the UCM filter and the conventional filter shows significant differences in all spatial frequencies. The readings of the UCM filter are much closer to the readings obtained without any filter than the reading obtained with the conventional filter (figure 17).


Figura 17. Near vision contrast sensitivity with/without protective welding filters: without filter vs conventional filter vs UCM-proposed filter. *Significance p<0.05 between the CS readings with filter vs analysed filter.

DISCUSSION

Photochemical retina damage was discovered in 1965 by Noell, who found out serendipitously that albino rats’ retinas could be damaged irreversibly by simple exposure of several hours or days to ambient light within the intensity range of natural light. This same damage might also occur in pigmented rats when the pupils are dilated. Other studies, like that of Wu et al from 2006, show that photochemical retina damage occurs with varying morphology in different animals.

The phototoxic effects of light on the retina have often been studied by acute animal exposure to intense light. These studies have recorded the capacity of light, under certain circumstances, to cause cell death of photoreceptors and the retina pigment epithelium by apoptosis and by a mechanism involving rhodopsin (Reme et al., 2005; Wenze et al., 2005). Moreover, exposure to permanent light (Noell et al., 1966; Law-will, 1973; Tso, 1973; Tso and Woodford, 1983; Dureau et al., 1999) produces a thinning of the external nuclear layer, indicative of receptor reduction. The exact mechanism causing these changes is not yet known, although it is probable that the initial lesion occurs in the external segments of the photoreceptors (Organisciak et al., 1994).

According to Wu’s bibliographic trawl, the light toxicity intensifying factors found to date in animal studies are: wavelength (Grimm et al., 2000 ); light intensity and exposure duration (O’Steen et al., 1979); cumulative light effects (Noell, 1966; Organisciak et al., 2010); circadian rhythm (Duncan, 2002; Organisciak et al., 2010); the adaptive state: (Noell et al.,1966); age (O’Steen et al., 1982) and genetics (Noell et al., 1971).

Several studies have been conducted to find out the wavelengths that cause the highest level of retina damage. Noell et al., in 1966, showed that retina tissue deteriorated when exposed to short wavelength radiation. Other studies like that of Okuno et al., in 2002 echo these findings, concluding that the sun, arc welding, plasma cutting and discharge lamps produce very high effective radiance with permissible exposure times of only 0.6 to 40 s, suggesting that visual exposure to these light sources is very dangerous for the retina.

In the interests of the best understanding of this discussion, it should be pointed out here that acute exposure to intense light causes thermal damage, whereas chronic exposure to less intense light produces photochemical damage (Margrain et al., 2004). Retina damage from exposure to welding blowtorch radiation is both acute and chronic, since the acute exposure to intense light occurs on and off throughout the worker’s whole working life. That is why this study kicked off with an account of the most important studies into light-induced neurodegenerative processes. The second part of this discussion comments on some characteristics of the radiation retina damage from welding devices.

The first references to welding-induced retina lesions came in studies conducted by Terrien back in 1902 (Choi et al., 2006). The following quote has been found in the works examined: «(...) all welding processes involve potential risks that might lead to diverse eye pathologies and damage» (Arend, 1996; Tenkate et al., 1997; Okuno, 2001; Kim et al., 2007; Peng et al., 2007; Okuno, 2010). It has been reported that 38.3% of occupational accidents in the construction industry correspond to welding, demolition with hammers and grinding (Woo, 2006). The high percentage of affected welders is due to the fact that this activity produces skin burns and damage and the lung disorders caused by welding fumes, such as dyspnea, rhinitis, asthma, pneumonia, lung cancer, among others (Meo et al., 2003). But welding damage also includes eye irritation, photokeratitis, cataracts, pterygium, among others (Okuno et al., 2001; Meo et al., 2003). All this possible damage means that it is important to ascertain the level of radiation given out by welding devices to assess the potential risks and take protection measures against them (Okuno et al., 2001). Welders must also be instructed about the possibility of suffering damage to the anterior and posterior segments of the eye and the need of wearing goggles to avoid this damage (Arend et al., 1996).

THIS STUDY PUTS FORWARD A FILTER THAT SHIELDS WORKERS FROM HARMFUL RADIATION WHILE ALLOWING THROUGH LESS ENERGETIC WAVELENGTHS TO ENSURE PROPER VISION OF THE WORKING AREA

Many studies agree about the need of wearing goggles or face shields for the welding processes on the grounds that high levels of UV radiation cause serious eye disorders (Arend, 1996; Tenkate et al., 1997; Okuno, 2001; Kim et al., 2007; Peng et al., 2007; Okuno, 2010). Protective systems must therefore provide the worker with sufficient protection for carrying out their daily work without exceeding the maximum permissible exposure (MPE). To check whether eye protection equipment complies with this requisite, Tenkate, in 1997, measured the exposure of a group of welders to ultraviolet radiation using a photosensitive polymer film. The polymer was stuck to the inside surface of the eye protection shield and showed that the estimated average ocular exposure inside the helmet was between four and five times the MPE. These results suggested that additional eye protection was necessary to complement conventional welding helmets.

Tenkate’s findings were borne out by further studies reporting cases of retina damage in welders wearing their goggles properly. The subsequent examination of protective filters showed that they absorbed only wavelengths less than 380 nm and could offer protection only against photokeratitis (Arend et al., 1996; Choi et al., 2006). This shows the need for a detailed study of the requirements of a protection system according to the type of radiation emitted.

After these studies Maier et al., in 2005, and Peng et al., in 2007, analysed different protection filters and demonstrated that these protect workers from the harmful radiation emitted by welding devices. At the end of the study Maier even concluded that “Welder’s Maculopathy” or “welding arc maculopathy” results from a neglecting of safety regulations rather than intrinsic risk. This study has measured the absorbance of diverse eye protection devices for welders. In keeping with the studies of Maier and Peng, UV transmittance was found to be zero. But after analysis of the visual perception tests we conclude that the workers’ improper use of the protection equipment should not be considered to be «negligence» but rather a self-defence mechanism to avoid burns to hands and arms. Indeed our results show that the conventional protection systems cut down visual acuity by up to 58% in comparison to non filter use. Bearing in mind that the torch emits flames at over 3500º C, the need of ensuring proper vision of the working area is crucial to avoid burns to the hands and welding errors.

Another important publication, presented by Chou et al. in 1996, sets out the results of a study conducted in a vehicle assembly plant. This study showed that one of the main occupational welding risks, besides the torch radiation, is the high-speed droplets of molten metal produced by the welding process. This peril obliges welders to wear an eye shield, obviously fitted with an ocular filter, against these flying pieces of molten metal. The problem is that welders often have to work in dark sites and cramped spaces, thus reducing their visual perception; in these situations some welders take off their goggles to carry out the work (Kim et al., 2007). In keeping with Kim’s results this study shows that the conventional protection devices currently available to welders considerably cut down their visual perception.

To obviate vision hindrance without having to remove the face shield, this study proposes a selective waveband optical filter that absorbs nearly all short wavelengths while merely attenuating the other wavelengths of the visible spectrum; the protective elements also block UV radiation. The final solution protects workers from harmful radiation while allowing through less energetic wavelengths to ensure uncluttered vision of the working area.

This study has therefore evaluated different aspects of visual perception, finding that both visual acuity and contrast sensitivity are hardly affected by the UCM-proposed filter whereas visions losses are considerable with the conventional filter. Stereoacuity is not significantly reduced by the UCM-proposed filter but losses, again, are considerable with the conventional filter. As for colour perception both filters produce a statistically significant reduction in colour discrimination, but the loss is much greater for the conventional filter (43%) than for the one proposed herein (5%).

CONCLUSIONS

  • Shortwave emission by oxyacetylene torches is double the emission of other wavelengths. The X-450 filter is sufficient for absorbing shortwave torch emissions, achieving zero transmittance in the 400-450 nm range. This means that a selectively absorbing optical filter can be designed, to eliminate most of the shortwave emissions and barely attenuate the other wavelengths of the visible spectrum.
  • To favour the use of welding protection equipment there is a need for a protection element that does not cut down the workers’ visual acuity. UCM’s filter complies with this remit whereas the conventional filter more than halves the workers’ resolution capacity.
  • To avoid skin-burn accidents due to a blinkered view of the working area, this study puts forward the UCM-designed welding filter, since it allows better contrast perception than the conventional filter.
  • The UCM-proposed optical filter is also recommended for better depth and relief perception in welding work. It does not affect depth perception, while the conventional filter cuts down stereoacuity significantly.
  • Both protective filters produce a reduction in colour discrimination, but the conventional filter much more than the one proposed herein. Nonetheless, colour discrimination is a not a crucial factor for welding work in comparison with other aspects of visual function, so it is not considered to be a fundamental comparison variable for both protective filters.
  • The different aspects of visual perception are drastically reduced by the conventional protective filter assessed in this study. On the contrary, the new protective filter proposed by the Universidad Complutense de Madrid holds the perceptive capacities assessed herein almost or even completely steady. It is therefore an optimal protection system for welding work, and is put forward as a benchmark filter for type approval by the competent authorities.

THIS STUDY SHOWS THAT CONVENTIONAL PROTECTION DEVICES CURRENTLY AVAILABLE TO WELDERS CONSIDERABLY CUT DOWN THEIR VISUAL PERCEPTION


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Occupational risk prevention for workers using oxyacetylene torches
Figure 5a. Blowtorch flame. This image clearly shows the blue colour of the flame, a telltale sign of short-wave emissions (very energetic and damaging to tissue).
Figure 5b. Metalworker carrying out a welding job.
Figure 9. Test of near vision acuity
Figure 10. VCTS Test, for near-vision contrast sensitivity.
Figure 11. Farnsworth-Munsell D-28 Test to assess colour perception.
Figure 12. Titmus Test
Figure 14. Near visual acuity readings with/without welding filters: without filter (WF) vs conventional filter vs filter proposed by UCM on logMAR scale.
Figure 15. Stereoacuity readings with/without welding filters: without filter (WF) vs conventional filter vs filter proposed by UCM.
Figure 16. Percentage of failures in the colour vision test with/without welding filters: without filter (WF) vs UCM-proposed filter.
Occupational risk prevention for workers using oxyacetylene torches Occupational risk prevention for workers using oxyacetylene torches