Health, safety and accident prevention
Control of welding fume
Exposure to fume
For many gas and arc welding processes, the fume concentration in the
immediate vicinity of the weld is well above its exposure limit. The amount of
fume generated is determined primarily by welding process, consumable and
welding procedure. However, the following aspects are likely to influence the
degree to which the welder is exposed to fume:
- welding position
- location and type of workplace
- exposure duration
Thus, welders using the same process may be exposed to different levels of
fume. The risks for each job should, therefore, be assessed individually.
Welding position
The welding position (flat, vertical, horizontal or overhead) and proximity
of the welder to the fume plume affect exposure. As the welder naturally bends
over the workpiece, the flat position induces the highest level of fume in the
breathing zone. The welder should adopt a working position which ensures that
his head is away from the plume.
Location and type of workplace
Welding in a large workshop, or outdoors, prevents build-up of fume and
gases. However, in a small workshop, fume will not be readily dispersed and the
welder may be subjected to a higher than average exposure. Working in confined
spaces, in particular, requires an efficient, monitored, ventilation system so
exposure is controlled and there is no depletion of oxygen in the working
atmosphere.
Exposure duration
Long and short term Occupational Exposure Limits (OELS) given in Job
Knowledge for Welders No. 31 relate to the average concentration over an eight
hour period. Exposure will be intermittent, mainly during the arcing period.
There should be relatively little exposure between arcing periods but this may
be influenced by the presence of other welders, effectiveness of control
measures and general ventilation. Furthermore, as the work pattern (arcing time
and down time) vary from day to day, average exposure may often only be assessed
by frequent sampling.
Control of welding fume
If welding fume cannot be eliminated, control measures should be adopted as
follows:
- choice or modification of the welding process
- improvement in working practices
- ventilation
- use of respiratory protection equipment (RPE)
RPE should not be considered until the effectiveness of all other techniques
has been explored.
Choice or modification of the welding process
Process choice is usually made on the basis of weld quality, economics and
equipment availability. Nevertheless, if other processes can be used, it should
be borne in mind that some processes, such as submerged-arc and TIG, generates
significantly less particulate fume than MMA, MIG and FCAW. Consumable
manufacturers also supply information on fume composition which can be used in
selecting welding rods for a particular job.
Improvement in working practices
A substantial improvement can often be made by placing the workpiece so the
welder can avoid the plume which rises above the weld.
In large scale fabrications, the welding sequence should be organised to
minimise the work carried out in enclosed or confined spaces.
Safe practice and accident avoidance
- adopt position and techniques to keep head out of welding plume
- avoid welding in enclosed and confined spaces
Ventilation
The strategy for using ventilation to control fume is shown above.
General ventilation may be adequate if welding is of short duration and
intermittent.
The most efficient way of controlling exposure to welding fume is its removal
at source. There are several methods of removing fume close to the weld:
Extracted benches
Extracted booth
Local exhaust ventilation (LEV)
On-gun extraction
As LEV and on-gun extraction systems are never 100% efficient, especially
when welding awkward structures, general ventilation may also be necessary to
control the background level of fume.
As each type of extraction equipment has limitations, it is important to
select the right equipment for each job. It is also essential that welders are
adequately trained to use the equipment and adopt good working practices.
Supervision is needed to ensure the equipment is being used effectively and to
minimise background fume level in the workshop.
Safe practice and accident avoidance
- check that the equipment is working correctly and is regularly maintained,
for example, cleaning and replacing filters according to manufacturer's
recommendations
- place the extraction hood or nozzle to capture the fume without disturbing
the gas shield
- when welding large structures, reposition the hood at appropriate
intervals to ensure fume continues to be effectively extracted
Respiratory protection equipment (RPE)
Where fume needs to be controlled, LEV should always be used to achieve as
much control as possible. If LEV is not possible, or there is still unacceptable
exposure, RPE is needed. RPE should always be the least preferred means of
control because it only protects the wearer. Other methods are all aimed at
preventing exposure whereas RPE is essentially curative. There are two types of
RPE:
- respirators - workshop air cleaned before being inhaled
- air-supplied - air supply is separate from workshop atmosphere
Selection of suitable RPE will require the advice of an expert who can make
the selection based on fume concentration, presence of toxic gases and whether
there is a oxygen deficient atmosphere.
Safe practice and accident avoidance
- Consult expert in choice of respirator
- Each welder to be personally fitted with an RPE to ensure that it provides
adequate protection
- Personnel to be trained in use of an RPE and its maintenance and cleaning
- Management to ensure systems exist for control of equipment and training
Publications and relevant standards
- EH 54
- Assessment of Exposure to Fume from Welding and Allied Processes,
HSE Books, 1990.
- EH 55
- The Control of Exposure to Fume from Welding, Brazing and Similar
Processes, HSE Books, 1990.
- HS(G)37
- An Introduction to Local Exhaust Ventilation, HSE Books, 1995.
- HS(G)53
- Respiratory Protective Equipment - a Practical Guide, HSE Books,
1990.
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