Diesel/Chemical fumes are known to contain Benzene.  Benzene is known to be a cause of Leukemia.  Railroad men are exposed to diesel fumes during their work careers.  Railroad men get Leukemia.  It would seem a logical conclusion that Leukemia in railroad men is caused by exposure to diesel fumes.  The medical link between the two must be proven by professional opinions.  Many professionals do believe in this link:

“Every level above zero [benzene] contributes to AML [Leukemia].”  Peter Infante, Dr. Ph.D., D.S.

“There is no safe level of exposure to benzene.”  Myron Mehlman, Ph.D.

“There is no safe level [benzene].”  Martyn Smith, Ph.D., N.C. at Berkeley.

It seems the next wave of railroad worker litigation will involve benzene exposure which leads to Leukemia (AML & ALL) and other cancers.