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Contrinex Industrial Electronics
METHODS FOR DETERMINATION OF RISK
LEVEL
The methods used for assessing the risks associated with a specific
machine are addressed by several standards. Standards either impose
or recommend corrective measures that will establish an adequate
level of safety.
DETERMINATION OF RISK LEVEL IN NORTH AMERICA
In order to select the appropriate safety device adapted to the actual
risks and dangers, it is important to assess the risk. ANSI B11.TR3-
2000 provides a “Risk Estimation Matrix” in order to determine the level
of risk depending on the cross-referenced factors of the probability of
harm occurrence and harm severity:
PROBABILITY
OF HARM
OCCURRENCE
SEVERITY OF HARM
CATASTROPHIC
SERIOUS
MODERATE
MINOR
Very Likely
High
High
High
Medium
Likely
High
High
Medium
Low
Unlikely
Medium
Medium
Low
Negligible
Remote
Low
Low
Negligible
Negligible
TABLE 3 : RISK ESTIMATION MATRIX AS PRESENTED BY ANSI B11.TR3-2000
The purpose of assessing the risk is to determine the appropriate level
of safety. It is important that the protective device complies with the
determined risk and is adapted to the machine control system. Risk
assessment applies to each element that makes up the safety system,
and not just the protective device itself. In particular, safety devices can
only be used on machines that comply with control reliability as de-
scribed in OSHA 29.1910.212 and ANSI B11.19-20.
Another important point to be considered is the life cycle of the machine
and its protective devices. The safety of any machine will diminish with
time due to the deterioration of components, wear, loosening of parts,
etc. It is therefore important to conduct regular inspections in order to
detect defects that may lead to reduced safety, and to effect the neces-
sary repairs before the level of risk exceeds the original assessment.
DETERMINATION OF REQUIRED PERFORMANCE LEVEL (PL
r
)
EN/ISO 13849-1 sets out a procedure for the selection and design of
safety measures. The procedure contains the following 6 steps:
1. Identify the safety functions to be performed
2. Determine the required Performance Level
3. Design and technical realisation of the safety functions
EN 13849
