Safety guards and their monitoring and signal processing systems have to satisfy variously high requirements, depending on the degree of potential danger to persons and machines. Possible realization forms extend from a simple mechanical-action position switch to a self-monitoring locking mechanism with start-up testing. The requirement level which should be satisfied in an individual case can be determined in a risk analysis that takes into account the danger parameters.

Risk estimation according to EN 954-1

The method described in this standard permits the risk involved in a particular application to be estimated on the basis of a few parameters which are characteristic for the risk. This risk analysis allows determination of a so-called requirement class from a predefined classification scheme.

S – Severity of injury

• S1 - Sligth (normally reversible) injury
• S2 - Serious (normally irreversible) injury including death

F - Frequency and/ or exposure time to the hazard

• F1 - Seldom to quite often and/or the exposure time is short
• F2 - Frequent to continous and/or the exposure time is long
  

P - Possibility of avoiding the hazard

• P1 - Possible under specific conditions
• P2 - Scarcely possible

B, 1 – 4 Categories for safety-related parts of control systems

		Preferred categories for reference points
		Possible categories which can require additional measure
		Measures which can be over dimensioned for the relevant risk