Which substance is primarily recognized as a carcinogen in refinery processes?

Benzene is primarily recognized as a carcinogen in refinery processes due to its established links to various forms of cancer, particularly leukemia. The International Agency for Research on Cancer (IARC) classifies benzene as a Group 1 carcinogen, which indicates sufficient evidence of its carcinogenicity in humans. Benzene is commonly found in crude oil and is released during refining processes. Workers at refineries may be exposed to benzene through inhalation or skin contact, making it a significant concern for occupational health.

The other substances listed, while they may have other health effects, do not carry the same level of recognized carcinogenic risk as benzene. Ethylene, propylene, and butane are generally considered to have lower toxicity profiles regarding cancer risk in comparison to benzene. In particular, ethylene is primarily used as a building block for plastics and does not have the same prevalence or classification as a cancer-causing agent.