EPSC Learning Sheet

Hydrogen Sulphide Explosion

Published 3 February 2020



What Happened?

The vacuum breaker on a tank for molten sulphur was plugged blocking the air sweep gas flow, resulting in elevated H2S concentration. An ignition source created an explosion.

H2S dissolves from the molten Sulphur



Vacuum breakers can foul on the inside when products condens or solidify at a lower temperature on the top of the tank

Ventilation systems in sulphur tanks are safety critical and their function must be validated e.g. by a low flow alarm

H2S Lower Explosion Limit drops to about 3.3% at the elevated temperature applied to keep the Sulphur molten

In this case the ignition source might be from a spark related to flowing molten sulphur, that is an accumulator for electrostatic charges (here during a truck loading)

Grounding and bonding of sulphur tanks is critical, as well as follow-up of the EX zone inside the tank

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