Symbol 3616 from ISO 7000 - Title/Meaning: Gas, heavier than air 
Function/description: To identify that the gas container or system (e.g. in a vehicle) contains gas that becomes heavier than air when released
Own work using: iso.org/obp/graphics/grs/d3a3cf9e-4870-465a-b210-bd51f3154c88 200.png
Vectorization:  Mrmw