Benzene (C6H6)

Benzene (C₆H₆) is a volatile, sweet-smelling aromatic hydrocarbon and a confirmed Group 1 human carcinogen (it causes leukaemia and other blood cancers). Because of this, it is one of the few individual VOCs given its own NAAQS limit: an annual ambient average of 5 µg/m³. There is no fully safe level — the limit reflects an acceptable-risk threshold, not a no-harm threshold.

Benzene evaporates readily and is present in petroleum fuels and many process streams. It is released from petroleum refining, fuel storage and dispensing, solvent use, and the incomplete combustion of organic material. In thermal cracking of hydrocarbons — exactly what happens in plastic and tyre pyrolysis — benzene and other aromatics (toluene, xylene, styrene) are formed in the pyro-oil and the non-condensable gas, making aromatic-VOC exposure a core occupational hazard of these sectors.

The danger to a recycler is largely worker exposure: benzene is absorbed by inhalation of vapour during pyro-oil handling, tank gauging, and any open transfer of aromatic-rich liquids, and through skin contact. Chronic low-level exposure, common in poorly ventilated informal pyrolysis yards, is the real risk rather than acute poisoning. It is also a contributor to ambient VOC load and ozone formation.

Control is exposure-focused: closed-loop handling of pyro-oil and aromatic solvents, vapour recovery on storage tanks, local exhaust ventilation at transfer points, and avoidance of open decanting. Personal protection (organic-vapour respirators, gloves), routine workplace air monitoring for benzene, and worker rotation limit chronic dose. Ambient benzene is tracked in NAAQS monitoring, and pyrolysis operators should treat it as a serious health-and-safety obligation, not just an air-quality number.