E/E/PE - Electrical/Electronic/Programmable Electronic – e.g. E/E/PE Safety-related system.

EUC - Equipment Under Control.

Functional Safety - Functional safety is the part of the overall safety of plant and/or equipment that depends on the correct functioning of safety related systems and other risk reduction measures including alarms, trips and interlocks.

Interlocks/Interlock System – the term used throughout SHE Code 40 to describe E/E/PE Safety-related systems in STFC.

Harm - Physical injury or damage to the health of people or damage to equipment, property or the environment.

Hazard - Potential source of harm.

Hazardous Situation - Circumstance in which people, property or the environment are exposed to one or more hazards.

Safety Integrity - A measure of the rate of unsafe failures; the likelihood of a safety-related system satisfactorily performing the required safety functions under all the stated conditions, within a stated period of time.

Risk - combination of the probability of occurrence of harm and the severity of that harm.

Residual risk - risk remaining after protective measures have been taken.

Safety - freedom from unacceptable risk.

SIL - Safety Integrity Level - A target probability of dangerous failure of a defined safety function; a discrete level (one of 4) for specifying the safety integrity requirements of safety functions.

Tolerable risk - risk which is accepted in a given context based on the current values of society or, in the context of STFC, within the Corporate Risk Appetite.​