What is harm?

Harm id defined as “injury or damage to the health of people, or damage to property or the environment”.


What is risk?

Risk is defined as the “combination of the probability of occurrence of harm and the severity of that harm”. This can be resumed as

Risk = probability of occurrence of harm x severity of that harm


What is safety?

Safety is defined as “freedom from risk which is not tolerable”. This means that a tolerable risk is still present. This is an accepted risk in a certain the “context based on the current values of society”.


Occurrence of Risk

When a risk is considered present? Take a look to the picture here below.



A snake alone is in the picture on the left. It is a hazard, but it alone is not enough to cause harm.

A person is also in the picture on the right. This introduces the possibility of harm occurring the snake snatched the person. The picture on the right indicates a situation in which “risk” exists.


What are risk assessment and risk reduction?

The risk assessment is an overall process comprising a risk analysis and a risk evaluation. The risk analysis consists in a systematic use of available information to identify hazards and to estimate the risk. The risk evaluation procedure based on the risk analysis to determine whether tolerable risk has been exceeded.

The risk reduction consists is action or means to eliminate hazards or reduce risks.

“The iterative process of risk assessment and risk reduction for each hazard is essential in achieving tolerable risk”.

The following procedure should be used to reduce risks to a tolerable level:

  1. a) identify the users for the product or system, including vulnerable consumers and others;
  2. b) identify the intended use of the product or system and assess the reasonably foreseeable misuse;
  3. c) identify each hazard (including reasonably foreseeable hazardous situations and events) arising

in the stages and conditions for the use of the product or system, including installation, operation,

maintenance, repair and destruction/disposal;

  1. d) estimate and evaluate the risk to the affected user group arising from the hazard(s) identified;
  2. e) if the risk is not tolerable, reduce the risk until it becomes tolerable.

The first 3 standards listed here below are harmonised to the Machinery Directive and the last one to the ATEX Directive.

EN ISO 13849-1:2008 Safety of machinery - Safety-related parts of control systems - Part 1: General principles for design (ISO 13849-1:2006)
EN ISO 13849-1 provides instructions for system design, integration and validation. The standard can be used for the safety-related parts of control systems and various kinds of machinery, regardless of the technology or energy source used. It also includes special requirements for safety-related parts that have programmable electronic systems. This standard thus covers the entire safety function for all included devices (i.e. a complete safety chain such as sensor-logic-actuator).
EN ISO 13849-1 defines how to determine the required Performance Level (PL) and how to verify the achieved PL within a system. PL describes how well a safety system is able to perform a safety function under foreseeable conditions. Five possible PLs are available: a, b, c, d and e. PL “e” has the highest safety reliability while PL “a” the lowest.
The standard has replaced EN 954-1:1996 since 1 January 2012.

EN ISO 13849-2:2012 Safety of machinery - Safety-related parts of control systems - Part 2: Validation (ISO 13849-2:2012)
EN ISO 13849-2 specifies the procedures and conditions to be followed for the validation by analysis and testing of the specified safety functions, the category achieved, and the performance level achieved by the safety-related parts of a control system (SRP/CS) designed in accordance with EN ISO 13849-1.

EN 62061:2005 Safety of machinery - Functional safety of safety-related electrical, electronic and programmable electronic control systems
EN 62061 is the standard for designing electrical safety systems. It includes recommendations for the design, integration and validation of safety-related electrical, electronic and programmable electronic control systems for machinery. It describes the SRECS using the Safety Integrity Level (SIL) as EN 61508 but only until SIL3. The entire safety chain is covered.

EN 61511-1, 2, 3:2004 Functional safety - Safety instrumented systems for the process industry sector
EN 61511 series offers significant value to operators and integrators in the process industry. It sets out practices in the engineering of systems that ensure the safety of an industrial process using instrumentation. Such systems are referred to as Safety Instrumented Systems (SIS). A SIS is composed of any combination of sensor(s), logic solver(s) and final element(s).

EN 50495:2010 Safety devices required for the safe functioning of equipment with respect to explosion risks
EN 50495 defines with SIL the required safety level for monitoring of potential ignition sources of electrical explosion protected equipment and the requirements on the safety level of the respective safety devices. The standard offers a simplified evaluation procedure for hardware reliability for non-complex safety equipment as well.