Static and flammables: the incident that was nearly ours

What happened

A customer bought twelve reconditioned 275 gallon containers from us for what they described on the order as "parts cleaning fluid". That description is accurate about a very wide range of products, some of which are aqueous detergents and some of which are naphtha-based solvents with a flash point around 40 °F. They had the second kind.

They filled the first container from a tanker through a two-inch hose, top-fill, free-falling into the container, at what a subsequent conversation established was somewhere near 90 gallons a minute. The operator noticed a crackling sound and a faint smell and stopped. Nothing ignited. They called us the next morning to ask whether the noise was normal.

It is not normal. It is the sound of a static discharge occurring in a vapour space that was almost certainly within its flammable range. The margin between that call and a very different call is not comfortable to think about.

The physics, briefly

Charge separation happens whenever a non-conductive liquid moves — through a hose, through a filter, or in free fall. Filters and turbulent flow are particularly effective at generating it. The liquid arrives in the container carrying charge, and because both the liquid and standard HDPE are excellent insulators, that charge has nowhere to go.

• The charge accumulates on the liquid surface and in the container wall.
• The potential rises as filling continues — this is why the risk peaks near the end of a fill, not at the start.
• Splash filling roughly triples charge generation compared with a submerged fill through a dip pipe.
• The vapour space above a flammable liquid at ambient temperature is, by definition, likely to be within its flammable range somewhere during the fill.
• A discharge into that space is an ignition source of entirely sufficient energy.

What a conductive IBC actually does

Conductive and antistatic IBCs use a bottle compounded to have a controlled surface resistivity — typically with carbon black — so that charge can migrate through the wall to a grounding point rather than accumulating. Combined with a bonded and grounded fill assembly, the charge drains as fast as it is generated.

Note that a conductive container on its own is not the answer either. The container, the fill assembly, the hose and the tanker all have to be bonded to each other and to ground, so that no two parts of the system can sit at different potentials. A conductive container with an ungrounded fill line is a more expensive version of the same problem.

What we changed

The root cause here was not a technical failure. It was an order form that accepted "parts cleaning fluid" and a sales process that did not ask the follow-up question. That is entirely on us.

1. Any order where the described contents could plausibly be flammable now triggers a direct question before we quote: what is the flash point, and do you have the safety data sheet?
2. If the flash point is below 140 °F, we do not quote a standard poly container. We quote conductive, or we quote a stainless unit, or we say that this is not something we should supply.
3. The order desk has a written list of product descriptions that trigger the question — "cleaner", "solvent", "thinner", "fuel", "degreaser" and about a dozen more.
4. We added a paragraph to the safe handling guide and to this blog, because the failure mode is not widely understood outside the chemical industry.

The container was correctly specified for what the order said. The order said the wrong thing, and we did not ask.

If you are storing anything with a flash point in a plastic container, and you are not certain the container is conductive and the system is bonded, stop and check. It costs an afternoon. The alternative is not proportionate.