Coal gas’s flammable constituents include carbon monoxide and hydrogen, ko te whakamutunga ka taka ki raro i te waahanga hau pahū o Class IIC. He rereke mai i te hau maori, mo e IIBT4 taputapu hiko pahū-pahū rawaka, Ko te waro hau e tika ana kia whakamahia te IICT4.
Mo etahi atu tohu haumaru, conducting gap tests or minimum ignition current experiments is advisable.