Safety Integrity Level (SIL): Functional Safety for Your Applications

One example is the purchase of heating oil. First, the desired amount of oil is specified in the form of a number together with the unit "liter". A dealer will then supply this heating oil using a suitable measurement method (usually a calibrated flow meter) to ensure that the quantity supplied corresponds to the quantity specified when the order was placed. Safety technology is similar, except that the need for safety is a top priority, and satisfying the need for a material asset is not necessary.

It is a well-known fact that technical equipment can pose a safety risk so dangerous that people should not be exposed to the equipment. In such cases, the relevant risks must be reduced to meet the need for safe operation. It must be possible to quantify (and measure) risk reduction in order to satisfy this requirement. As already mentioned, this is achieved using the SIL "unit", whereby only whole values are defined within a range from 1 to 4.

When risk reduction is complete, it must be proven that the extent of the risk reduction corresponds to the minimum required parameters (i.e., the SIL requirement). This approach results in the following procedure:

• 1. Risk analysis: Establish required risk reduction
  (specification of SIL requirement)
• 2. Implementing the risk reduction
  (install protective equipment)
• 3. Assessing functional safety
  (SIL evaluation of protective equipment)