It just smelled like sulfur....
Hydrogen Sulfide gas?
H2S is flammable and poisonous.
While such concentrations are not common, if gasses are released in a confined area, they could cause nausea, illness, and in extreme cases, death.
https://www.cleanwaterstore.com/resource/how-to-guides/how-to-treat-sulfur-odors-in-well-water/
Was he asthmatic?
I doubt they'd use that.
:: in extreme cases, death ::
Not really extreme cases. Short expose to just 100ppm of H2S will result in death.
A single breath of 1000ppm will result in death.
At 10,000ppm (1%), death can result from sinusoidal exposure; comes in through the eyes and ears.