Functional safety

Different types of risks

There are many different types of risks in technical systems:  mechanical risks, chemical risks, electrical risks, explosion risks etc.  When we say that a system, a piece of apparatus or a machine is safe, we mean that the risks presented by or to it are acceptably low. 
Safety, in other words, means that the system etc. does not present unacceptable risks of physical damage or health or injury risks.  Damage or injury can arise either directly or indirectly as a result of damage to property or the environment.  Functional safety is that part of overall safety that depends on whether a system or component operates correctly with the input signals that it receives. 

The difference between functional safety and electrical safety

Functional safety must not be confused with electrical safety, which is concerned with protection against electric shock and fires caused by electricity.
An example of functional safety is that of an overspeed trip to prevent a grinding wheel from running too fast, and thus introducing a danger of bursting.  However, mechanical protection against injury caused by the rotating wheel is not an aspect of functional safety, and nor is sound attenuation intended to protect against the risk of damage to hearing.  All these measures are important in assessing whether the grinder as a whole is regarded as sufficiently safe. 

Standards

• EN 62061 "Safety of machinery - Electrotechnical aspects" 
• EN ISO 13849 "Safety of machinery - Safety-related parts of control systems" 
• EN 61511 "Functional safety - Safety-instrumented systems for the process industry sector" 
• EN 61508 "Functional safety of electrical, electronic or programmable electronic safety-critical systems" (a total of seven parts) 
• ISO 26262 "Road vehicles - Functional safety"
• EN 61513 "Nuclear power plants - Instrumentation and control for systems important to safety - General requirements for systems"

EN 61508 is intended primarily to be used in connection with the design of individual components that will form part of a safety function, while IEC 61511 and IEC 62061 describe how the complete safety function should be implemented using components designed to comply with IEC 61508.

ISO 13849-1 is applicable both to the design of individual machine components and to the creation of the complete safety function in a machine.

ISO 26262 "Road vehicles - Functional safety" is used when designing safety critical vontrol systems within road vehicles