Flash fire during production operations caused by accumulated static charges in an inner storage tank

A well was opened under natural flow with diesel and water circulated in the annulus and wellbore.

The flare pilot was ignited, and surface facilities were lined up to a bituainer (number 3), with the separator bypassed.

An operator was at the sampling point to determine when the diesel had been circulated out.

The operator observed crude at the sampling point, so the flow was immediately directed to bituainer number 2 via the separator.

One hour later, an explosion and flash fire event occurred in bituainer number 2.

The explosion blew open the container’s manway cover and ejected the gasket 20 metres (65 feet) away.

The tank sustained minimal damages to its roof. Fortunately, there were no injuries to workers or environmental spill.

The inner tank was 280 µm thick, rather than the 50 µm (recommended practice at the time of the incident).

This thick coating created a barrier so that accumulated static charges had no way to dissipate safely from the inner tank to the external earthing on the outer skin.

The manway cover was not closed tight, allowing air into the bitutainer, leading to the formation of a flammable air-vapour mixture in the tank.

The turbine flow meter upstream of the bitutainer was faulty – it gave inaccurate volumetric readings of crude compared to actual dip measurements.

Due to the lack of a glass level indicator, the crew had to carry out visual checks of crude level. This required regular opening of the manway.

Lack of information on the physical properties of the crude oil extracted from that specific site - its electrical conductivity and the hazards of static electricity.

Minimise the potential for static discharge by following up to date guidelines and standards (e.g. recommended practice on static electricity).

Tanks used to store low conductivity fluids should have a coating thickness of less than 50 µm.

• The flow velocity of fluids which can contain flammable atmosphere should be no more than 1 m/s until the fill pipe is submerged in the fluid.

Technical data and information should be available so workers can understand the properties and behaviour of materials to be able to conduct suitable risk analysis.

What is the worst that could have happened?

What guidelines do you have to follow for your tasks,  and how do you know if they are up to date?

Do you fully understand the properties of the materials/fluids you are working with? What should you do if you need more information before starting the activity?

What pre-startup safety reviews do you carry out before starting work?

What measures do we have in place to prevent this from happening here? How can we improve?