It is unclear how Infection happens but one way is to be scarred or bruised by a mutants swing. The only HazMat member to survive Infection was Ethan Cole which had a mutant scientist swing its deadly claws. The other HazMat member to be infected was "Crispy" which mutated like all the other infected humans. However Ethan Cole was not mutated properly and the mutagen spread around his body not centered around his brain which would make him insane like all the other mutants. Instead the spreading of mutagen gave him special powers.