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98
Health hazards from gases
The potential hazards from breathing in gases during welding are:
1. Irritation of the respiratory tract. Ozone can cause delayed
irritation of the respiratory tract which may progress to bronchitis and
occasionally pneumonia. Nitrogen oxides can cause a dry irritating cough and
chest tightness. Symptoms usually occur after a delay of 4 to 8 hours. In
severe cases, death can occur from pulmonary oedema (fluid on the lungs)
or pneumonia.
2. Asphyxiation. There may be a risk of asphyxiation due to
replacement of air with gases produced when welding in a workshop or area
with inadequate ventilation. Special precautions are needed when welding in
confined spaces where there is the risk of the build up of inert shielding
gases. Carbon monoxide, formed as a result of incomplete combustion of fuel
gases, can also cause asphyxiation by replacing the oxygen in the blood.
Establishing safe levels of fume in the workplace
The COSHH Regulations* require that exposure is controlled below
specific limits. The limits, known as occupational exposure limits, are
detailed in EH 40 which is revised periodically. The majority of limits listed
are for single substances. Only a few relate to substances which are complex
mixtures; welding fume is one of these. It has an occupational exposure limit
but account must also be taken of the exposure limits of the individual
constituents. So, in considering what would be safe exposure levels to
welding fume, not only should exposure be controlled to within the welding
fume limit but also the individual components must be controlled to within
their own limits. The assessment of exposure to fume from welding processes
is covered in EH 54.
Substances may have a maximum exposure limit (MEL) or an
occupation exposure standard (OES).
A MEL is the maximum concentration of an airborne substance to
which people may be exposed under any circumstances. Exposure must be
reduced as far as is reasonably practicable and at least below any MEL.
An OES is the concentration of an airborne substance, for which (according
to current information) there is no evidence that it is likely to cause harm to a
person's health , even if they are exposed day after day. Control is thought to
be adequate if exposure is reduced to or below the standard.
The OESs and the MELs of some of the substances found in welding
fume are listed in Table below; the absence of other substances from this list
does not indicate that they are safe.
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