(CBS) – Reasons may be clearer now about why firefighters have higher rates of certain types of cancers.

CBS 2’s Chris Martinez previously reported on a study that showed firefighters are at-risk. The study also found Chicago firefighters are more than twice as likely to develop them.

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More research shows why that may be happening.

The research looked at firefighters’ exposure to chemicals released when homes burn and their exposure after.

“Some of them range from known carcinogens to possible or potential carcinogens,” Gavin Horn of the Illinois Fire Service Institute says.

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Horn is a co-author of a study involving Chicago firefighters that measured levels of certain chemicals coming off their gear 25 minutes after the fire. Researchers also tested firefighters’ breath.

The study found known cancer-causing chemicals, benzene and styrene, were at more than five times higher than pre-burn levels coming off their gear. It also found those same chemicals more than two times higher in the firefighters’ breath.

“The concern is repeated exposure to these as well, over a career or multiple fires, it could become a significant problem,” Horn says.

The biggest problem is exposure to the chemicals once firefighters remove their breathing apparatus. It’s thought the chemicals are absorbed through the skin or inhaled.

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Additional studies will look at ways to decontaminate that gear after a fire.