Functional Safety standards by sector

Further than IEC 61508, other standards define the rules on how to correctly implement/extend these minimum requirements to specific sectors.

Some examples of standards by sector

The most important Functional Safety standards by sector are:

• ISO 13849 Machine Safety
• EN 50126/8/9 Railway
• IEC 61800-5-2 Electrical Drivers
• IEC 61513 Nuclear Sector
• EN 60601 Medical Devices
• IEC 50156 Furnaces
• IEC 61511 Process Industry
• IEC 62061 Machinery
• ISO 26262 Automotive
• IEC 61131-6 PLC

In particular, regarding machinery, in Europe equipment designed to be used specifically to implement a safety function falls within the scope of Machinery Directive 2006/42/EC according to the definition of “safety components”:

The Machinery Directive defines a “safety component” a component:

• which serves to perform a safety function,
• which is placed on the market independently,
• whose failure and/or malfunction puts the safety of persons at risk, and
• which is not necessary for the operation of the machine or for which normal components can be replaced.

Functional Safety applied to Machine Safety

Even though IEC 61508 is the basic reference for Functional Safety, to declare the conformity against Machinery Directive 2006/42/CE it is necessary to apply the additional requirements to machinery specific sector.

The best way to declare conformity is to follow the requirements of the applicable standards. Looking at the list of the harmonised standard, we find that the only two functional safety standards are:

• EN 62061 – Machinery
• EN ISO 13849 – Machine Safety

Both standards are “valid” to declare conformity; manufacturers can choose which best suits their needs.

Functional Safety according to ISO 13849

EN ISO 13849 provides safety requirements and guidelines on principles for the design and integration of safety-related parts of control systems (SRP/CS – Safety-Related Parts of Control system), including software design.

For SRP/CS, it specifies features that include the performance level required to perform safety functions. It applies to SRP/CS for high-demand and continuous mode, regardless of the type of technology and energy used (electrical, hydraulic, pneumatic, mechanical, etc.), for all types of machinery.

Specifically, EN ISO 13849:

• Introduces the PL (Performance Level) concept of the safety-related parts of the control system by making a comparison with SIL;
• It defines, in line with IEC 62061, that the maximum permissible SIL applied to machinery is 3 (SIL 4 remains applicable to other sectors such as the process industry);
• Redefines (without changing the main concept) the applicable failure rates and their calculation;
• Suggests how to analyse the risks associated with industrial machinery;
• Limits the applicability of functional safety solely to high-demand or continuous mode.

In addition, EN ISO 13849 suggests a way to analyse the risks associated with industrial machinery. The standard contains, in Annex I, a  risk graph that helps define the associated PL (PLr), knowing the parameters of severity, frequency and avoidance of each specific risk.