Ventilation

Ventilation can remove heat from the environment and reduce exposure to fumes and other atmospheric contaminants in the work area.

There are three main types of ventilation:

− local exhaust ventilation
− forced dilution ventilation, and
− natural dilution ventilation.

The choice of ventilation system should take into account:

− the toxicology of the fumes being generated
− the amount and type of fumes and contaminants produced
− the proximity and location of the welding process relative to the ventilation system
− the level of ventilation, natural or mechanical, both for the whole workplace and the welding area—this will also depend on screens and partitions which may restrict cross-flow at the work area
− the proximity of the welder’s breathing zone to the fume source, and
− the need to maintain a safe oxygen level and ensure the concentration of flammable gas, vapour, mist or fumes stays below 5 per cent of the lower explosive limit (LEL).

Local exhaust ventilation
A local exhaust system may comprise the elements listed:

− a hood which captures the contaminant close to its point of generation
− a duct system to move contaminant away from the work area
− an air cleaning system to prevent pollution of the general atmosphere
− an exhaust fan to provide air flow, and
− a stack or other means of discharging the decontaminated air into the atmosphere.

Local exhaust ventilation systems should be designed to provide a minimum capture velocity at the fume source of 0.5 m/second away from the welder. Inlets and outlets should be kept clear at all times. Air from a local exhaust ventilation system should not be re-circulated into the workroom. This air should be discharged into the outside air away from other work areas and away from air-conditioning inlets or compressors supplying breathing air.

Figure 1 Portable exhaust ventilation system

Examples of local exhaust ventilation suitable for welding operations include:
− fixed installations, such as side-draught or down-draught tables and benches, and partially or completely enclosed booths
− portable installations, such as movable hoods which are attached to flexible ducts