Explosion caused by ignition of paint vapour

A member has reported the following incident, whereby an explosion occurred in a tank on a barge. Fortunately, nobody was injured, but the incident resulted in significant structural damage to the barge.

The water tank had been painted and the second coat of a three-layer epoxy coating system had been completed, 48 hours prior to the explosion. During the paint curing period, the tank hatch cover had been left open for ventilation, but no mechanical blowers or extractors had been provided. This allowed solvent vapours – emitted from the coating materials – to build up inside the tank, forming an explosive atmosphere. Vapours escaped from the tank to the surrounding area via the open tank hatch. This vapour trail eventually reached a source of ignition – an electric fan being used to ventilate an adjacent tank approximately 5-6 metres from the tank hatch. This electric fan was not ex-rated. The vapour trail ignited, causing a flash back to the tank hatch, resulting in an explosion inside the tank.

Under normal atmospheric conditions, the solvent vapours are heavier than air. There was, however, no breeze that evening, allowing the vapours to seep through the tank hatch and along the deck, forming a vapour trail several metres long. The vapours were at a temperature above their flash point (25°C), as the ambient temperature was 31°C.

The company has identified the root cause of the incident to be lack of ventilation during the curing period, mainly due to:

• lack of technical and product safety information on site; combined with;
• limited technical.

The company involved found, on investigation, that neither the painting contractor nor the manufacturer’s representative had attended the risk assessment meeting and that the risk of explosion during the curing period had not been identified or assessed. The appropriate material data sheets for solvents and the paint were not available on site, nor was the manufacturer’s code of safe practice for tank lining applications.

The company has subsequently made thirteen recommendations to prevent such an occurrence happening again, including:

• the need for all safety-critical tasks involving sub-contractors/suppliers to be subject to a formal risk assessment;
• operations, marine and warehouse management need to ensure that all material safety data sheets and applicable codes of safe practice are available, understood and followed during the storage, handling and use of chemicals, solvents, paints and other dangerous substances.