The use of personal safety equipment should always be seen
as a last resort, only to be adopted when all else has failed. As
regards exhaust gases, the practical possibilities are limited, since
all of the pollutants contained in the emissions are difficult to
filter out, which generally rules out the use of masks and the like.
Consequently, if the problem is to be solved using personal safety
equipment, breathing apparatus must be used. Such apparatus is inconvenient
in practice because the oxygen must come either from cylinders carried
or worn on the back of the user or through a hose.