Where the hazardous gas, vapour, dust or fumes contemplated in subregulation (2) are of an explosive or
flammable nature, an employer or user of machinery shall further take steps to ensure that such a confined space
is entered only if -
(a) the concentration of the gas, vapour, dust or fumes does not exceed 25 per cent of the lower explosive limit of the gas, = vapour, dust or fumes concerned where the work to be performed is of such a nature that it does not create a source of ignition; or
(b) such concentration does not exceed 10 per cent of the lower explosive limit of the gas, vapour, dust or fumes where other work is performed.