Radiation is emitted by the welding arc in three principal ranges:-
Table 1
| Type | Wavelength
(nanometres) |
|---|
| Infrared (heat) |
>700 |
| Visible light |
400-700 |
| Ultraviolet radiation |
<400 |
These types of radiation do not cause ionisation of body tissue, but they can still cause damage to body systems and membranes.
Ultraviolet radiation (UV)
UV is generated by all arc processes. Excess exposure to UV causes skin inflammation, and possibly even skin cancer or permanent eye damage. However the main risk amongst welders is for inflammation of the cornea and conjunctiva, commonly known as 'arc eye' or 'flash'.
Arc eye
Arc eye is caused by UV radiation. This damages the outmost protective layer of cells in the cornea. Gradually the damaged cells die and fall off the cornea exposing highly sensitive nerves in the underlying cornea to the comparatively rough inner part of the eyelid. This causes intense pain, usually described as 'sand in the eye'. The pain becomes even more acute if the eye is then exposed to bright light.
Arc eye develops some hours after exposure, which may not even have been noticed. The 'sand in the eye' symptom and pain usually lasts for 12 - 24 hours, but can be longer in more severe cases.
Fortunately, arc eye is almost always a temporary condition. In the unlikely event of prolonged and frequently repeated exposures, permanent damage can occur. A person would have to be stubborn and/or foolish to allow himself to be repeatedly exposed to such arc eye risks without taking some precautions.
Treatment of arc eye is simple, rest in a dark room. Various soothing anaesthetic eye drops can be administered by a qualified person, or hospital Casualty Departments. These can provide almost instantaneous relief.
Ultraviolet effects upon the skin
The UV from arc processes does not produce the browning effect of sunburn; but does cause reddening and irritation caused by changes in the minute surface blood vessels. In extreme cases, the skin may be severely burned and blisters may form. The reddened skin may die and flake off in a day or so. Where there has been intense prolonged or frequent exposure, skin cancers can develop, but there is little evidence of this in welders.
Visible light
Intense visible light particularly approaching UV or 'blue light' wavelengths, passes through the cornea and lens and can dazzle and, in extreme cases, damage the network of optically sensitive nerves on the retina. Wavelengths of visible light approaching the infrared have slightly different effects but can produce similar symptoms. Effects depend on the duration and intensity and to some extent upon the individual's natural reflex action to close the eye and exclude the incident light. Normally this dazzling does not produce a long-term effect but in welders it is thought to progressively reduce their ability to adapt to extreme light conditions.
Infrared radiation
Infrared radiation is of longer wavelength than the visible light frequencies, and is perceptible as heat. The main hazard to the eyes is that prolonged exposure (over a matter of years) causes a gradual but irreversible opacity of the lens. Fortunately, the infrared radiation emitted by normal welding arcs causes damage only within a comparatively short distance from the arc. There is an immediate burning sensation in the skin surrounding the eyes should they be exposed to arc heat. The natural human reaction is to move or cover up to prevent the skin heating, which also reduces eye exposure.
There is very little evidence that welders can be exposed to the required intensity of radiation long enough for lens cataracts to be formed by infrared radiation. Oxy-fuel cutting can also emit high levels of infrared radiation and it is recommended that anti-flash, or impact resistant, eye protection is worn by anyone continuously engaged in heating or thermal cutting processes.
Avoiding the hazards
Although there are differing effects from UV, visible and infrared radiation, there is one common protection mechanism that is completely effective; this is to provide a barrier to prevent the radiation reaching sensitive surfaces. The welder should therefore be equipped with protective equipment as indicated below. It should not be forgotten that radiation can be reflected off shiny surfaces, and several cases of arc eye attributable to unwanted reflections have been recorded. The walls, etc, of the work area should have a matt finish.
Eye protection
The welder protects his eyes by means of a filter glass to absorb the radiation in the dangerous wavelengths, and limit visible light so he can see the progress of the welding process. There are two basic types: permanent filters, and photosensitive filters which react rapidly to the incident light from the arc and darken.
BS EN169 specifies a range of permanent filter shades of gradually increasing optical density which limit exposure to radiation emitted by different processes at different currents. It must be stressed that shade numbers indicated in the standard and the corresponding current ranges are for guidance only.
The operator's own preference and the application should be taken into account when selecting the shade number for a particular task. Standard filter glasses are now marked with the CE mark showing they have been independently tested to meet the full requirements of the standard.
BS EN 379 defines requirements for the photosensitive variable density lenses that are now available. These can be used with complete confidence, as there are failsafe requirements in the standard such that even if the lens does not darken when the arc is struck, dazzle may occur but no permanent eye damage will result. The overriding benefit of such reactive lenses is the welder's ability to see and position the electrode correctly before striking the arc. This can greatly reduce arc initiation defects.
Although arc-eye and other radiation effects appear to be the most significant hazards for welders, more than half all eye injuries are caused by flying particles of slag, grinding, chipping etc. It is therefore strongly recommended that anyone working close to arc welding activities should wear some eye protection even when arcing has stopped.
Head and face protection
Filter glasses are relatively small and are mounted in a dark, opaque shield, either hand-held or pivoted on a head-band so it can be raised or lowered by a movement of the head. The shield has to be designed to screen the entire face, ears and portions of the neck from the direct radiation from the arc. BS EN 175 lays down requirements for the basic types.
Gloves/gauntlets
Hands are usually the closest part of the body to the arc and the work piece. It is therefore important that welder's gloves provide thermal insulation as well as blocking out UV and visible light frequencies. The gloves should be designed to cover hand and wrist and overlap the sleeves.
With manual metal arc and MIG/MAG processes, spatter can also be a problem, and therefore gloves need to be able to resist penetration by droplets of molten metal. The combined effects of UV and ozone can rapidly degrade many glove materials. The durability of the material has to be taken into account in relation to the process control requirements. For example, tightly woven cotton or supple leather gloves may be ideal for low current TIG welding where a delicate control of the torch is required, but where little heat, and no spatter is generated. For most other arc welding processes, which emit high levels of radiation and spatter, much heavier or more substantial gloves are required.
Clothing
Almost any heavy-duty, dark coloured, opaque fabric will block UV and infrared radiation. However, as with gloves, damage by spatter and the combined effects of UV/ozone may be significant, depending upon the application. The welder's clothing must cover all parts of the body, arms, neck and chest that could otherwise be exposed to direct arc radiation.
Heavy-duty cotton overalls are usually the minimum required for protection. Man-made fibres and plastics are not suitable as they may be melted by spatter or even infrared heat. British Standard BS EN 470-1 specifies the design features and the spatter resistance for clothing suitable for welders.
It is important to prevent the welder from becoming too hot. He will be close to a source of intense heat and a complete suit of heavy protective clothing might significantly increase his discomfort. Local protection in the form of chrome leather aprons, hoods, capes, spats, half jackets or knee-pads is effective. In this way the right degree of protection can be provided where required and the rest of the welder's body can be protected adequately and comparatively inexpensively, for example, by overalls.
Footwear, not normally subjected to radiation, is also important. It must be able to resist molten spatter falling on it from above, or being trodden on thus melting the sole. Ankle boots with anti-crush toecaps are recommended for all processes except TIG welding, where shoes (with protective toecaps) may be adequate.
Protection for welder's helpers
Anyone working regularly within 2m of a welding arc needs to be protected against skin and eye exposure in the same way as the welder. He should at least have overalls, gloves and a hand-held or head shield if required to look at the arc. Additionally, he should have anti-flash glasses with side pieces to protect from inadvertent arc eye hazards. The same recommendation applies to one welder working in comparatively close proximity of another. Welders frequently suffer arc eye from inadvertent exposure not to their own arc, but to that of another welder working one or two metres away from them.
Tinted anti-flash glasses may be selected from BS EN 169, scale number 1.2 - 4 for example. If the assistant is to work at a similar distance from the arc as the welder, then the same filter number should be selected for the assistant as for the welder.
BS EN 175 contains details of the specifications for robustness and impact resistance for the various types of eye/face protection available.
Contact lenses
Reports that radiation from arc processes can fuse contact lenses to the eye are entirely without foundation. The UK Employment Medical Advisory Service and others have investigated the subject and issued statements saying that there is no risk that contact lenses can stick to the cornea due to incident radiation from welding.
However contact lens wearers can still suffer arc eye, and must remove the lens immediately they feel any discomfort, which could be some hours after the actual exposure. Welding also exposes the eyes to heat and dust so that it maybe necessary to remove and wash the lenses more frequently than normal.
Eye protection for others
Where practicable screens, walls or partitions should be provided to stop any arc radiation reaching the eyes of others working or passing through the area. Partitions or walls should be painted with matt colours to minimise reflections and glare.
Screens or curtains can be either fixed permanently or on portable frames where welding can take place at various locations in a shop. Flexible translucent plastic material is available from welding distributors, which will positively filter out UV glare and the other harmful blue-white radiation.
Obviously opaque textile or plastic materials will also stop radiation and provide complete protection, but they also restrict visibility.
Most rigid polycarbonate or even ordinary glass windows will also reflect or absorb enough harmful radiation to prevent eye injury to someone observing an arc through the material. However obviously the glare will be transmitted and can cause dazzle if the observers and the windows are too close (i.e. closer than 3m to the arc). If such materials are to be used for prolonged observation of an arc, the supplier should be asked to confirm that the material is suitable.
If no screens or windows are possible, then safety must be provided by arranging that unprotected observers should not be allowed to approach closer than 10m to an arc. At this distance even a wilful observer who insists at staring at the arc for up to say 10 minutes would only be dazzled.
References
- Personal Eye Protection - Filters for welding and related techniques - Transmittance requirements and recommended use
- Personal Eye Protection - Automatic welding fillers
- BS EN 470-1 Protective clothing for use in welding and allied processes
- BS EN 175 Personal protection - Equipment for eye and face protection during welding and allied processes
- BS EN 166 Personal eye-protection - specifications
- IIS/IIW-1161-92 Eye damage from radiation in arc welding
- IIS/IIW-1082-90 Welder's eye injuries