What Process Safety Protects Against

Process plants hold large amounts of hazardous material and energy inside pipes, vessels and tanks. Oil, gas, chemicals, steam and electricity are all useful while they stay contained. The danger starts when they escape. Process safety is the discipline of keeping them inside, and of limiting the harm if they get out.

The central event is called a loss of primary containment (LOPC). It means an unplanned or uncontrolled release of material from its primary container — a pipe, a vessel, a tank, a hose — including releases of non-toxic and non-flammable materials such as steam or hot water. Small LOPC events happen on most sites. Large ones become fires, explosions and toxic clouds.

Two worked examples

Example 1. A small flange on a gasoline line weeps a few drops an hour. Nobody is hurt. It is still an LOPC event and a warning: the gasket, the bolting or the line is not as designed. If it is ignored, the leak can grow.

Example 2. A storage tank is filled past its safe level because a level gauge sticks. Fuel overflows from the roof vents and forms a large vapour cloud that later finds an ignition source. The same basic failure — material out of its container — now has a very different consequence.

Both events share the same cause type. What differs is the amount released, the material and what was nearby. Process safety therefore looks at the small events as seriously as the large ones, because they come from the same weaknesses.