Hydrogen Sulfide Explosion

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 liberated from the molten Sulphur 

Aspects:

1. Vacuum breakers can foul on the inside when products condense or solidify at a lower temperature on the top of the tank
2. Ventilation systems in sulphur tanks are safety critical and their function must be validated e.g. by a low flow alarm
3. H2S Lower Explosion Limit drops to about 3.3% at the elevated temperature applied to keep the Sulphur molten
4. 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)
5. Grounding and bonding of sulphur tanks is critical, as well as follow-up of the EX zone inside the tank

Conclusion:

Sulphur tanks need specific attention to avoid an H2S explosion

Source:

EPSC Learning Sheet , July 2019 - EPSC Learning Sheets are meant to stimulate awareness and discussion on Process Safety EPSC can not be hold liable for the use of this sheet     Questions or Contact via www.EPSC.be