The first off-nominal levels of benzene at the ISS were detected on 13 April, the NASA spaceflight.com news outlet reported on Sunday.
On 29 April, the levels of benzene started to rise on an "increasing trend," eventually breaking the 30-day Spacecraft Maximum Allowable Concentration. The Lab Trace Contaminant Control System at the ISS was activated in May, but the levels of benzene were still "slightly high", according to the NASA spaceflight.com news outlet.
The US air quality monitor on board the ISS failed this month, and the crew is waiting for a brand new monitor expected to arrive on the Progress MS-15 cargo spacecraft, set to be launched to the ISS on 23 July, to resume the search for the benzene source.
Benzene is a highly flammable chemical that is colorless and evaporates into the air very quickly. According to the US Centres for Disease Control and Prevention, benzene is widely used in the US and ranks in the top 20 chemicals for production volume. Benzene is toxic and cancerogenic at high levels of exposure, according to the Department of Health and Human Services.