Natural Gas and Tetrahydrothiophene

I am a respiratory physician I have had a two patients claiming exacerbation of asthma as a result of exposure to natural gas leaks within their working environment. Is there any information about this? Could the odourant Tetrahydrothiophene be responsible as there is nearly nothing on toxicity Is there any information out there that ive missed?

Occupational Asthma, Specialist, 3/11/2018, 3/11/2018,