Thief Hatch

Engineered Approach to Lightning Protection for Thief Hatch

Thief Hatch Fire

Thief hatches are used to relieve excess pressure that can build up inside low-pressure, steel, and fiberglass tanks. The thief hatch hinged opens at a predetermined set pressure and, once the overpressure has dissipated, the cover reseats onto the base. When excessive vacuum builds within a storage tank, the spring-loaded pallet lifts, breaking the seal between the seat and pallet, allowing vapors to pass through the valve orifice, and relieving the vacuum buildup.

During a lightning event, the current can arc over the pallet and the seat if they happen to be separated at that moment. This will ignite fires in both steel and fiberglass storage tanks.

Very low or high temperatures, with resulting low humidity, also increase the accumulation of electrostatic charge both while it is being generated and during the normal relaxation period. Accumulated static on the pallet and seat can also arc over during hot and dry days, causing fires and explosions similar to lightning.


Thief hatch ignited fires can be avoided with Petro Guardian’s engineered approach to grounding and bonding. Contact the team@petroguardian.com to find out how you can improve the integrity of grounding and bonding at your facility.