FUNCTIONAL SAFETY?
What is it?
Functional safety engineering involves identifying hazardous failures which lead to serious consequences and then establishing maximum tolerable frequency targets for each mode of failure.
A safety-function is thus defined as a function, of a piece of equipment or system, that maintains a safe state, or brings to a safe state, in respect of a particular hazard.
Equipment whose failure contributes to each of these hazards is referred to as "safety-related".
(words adapted from "Safety Critical Systems Handbook" by D. J. Smith and K. G. L. Simpson
SAFETY
Freedom from unacceptable risk of harm to people. Safety may also encompass environmental or asset damage/loss.
HAZARD
A potential source of harm. With a hazardous even being the occurrence of a hazard.
RISK
Risk is the probability a hazard occurs accompanied by the severity of the resulting outcome.
SIL
A measure of safety system performance in terms of reliability of probability of failure on demand. There are four safety levels SIL 1-4. The higher the SIL, the higher associated safety level and the lower the probability that a system will fail to perform properly.