6 Safety Manual
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Safe failure Failure of an element and/or subsystem, and/or system involved in implementing the safety
function, which
a) causes false triggering of the safety function, switching the EUC (or parts of it) to a safe
state, or maintaining a safe state; or
a) increases the probability of false triggering of the safety function, switching the EUC (or
parts of it) to a safe state, or maintaining a safe state.
Hazard Potential source of damage
Safety Freedom from unreasonable risk
Safety function A function that is performed by an E/E/PE safety-related system, safety-related system
based on other technology, or external equipment for reducing risk with the goal of
achieving or maintaining a safe state for the EUC taking into consideration a specified
dangerous event
Safety integrity The probability of a safety-related system performing the required safety function under all
specified conditions within a specified period of time according to requirements.
Safety integrity level (SIL) One of four discrete levels for specifying the requirement for safety integrity of the safety
functions assigned to the E/E/PE safety-related system. Safety integrity level 4 represents
the highest level of safety integrity, while safety integrity level 1 represents the lowest.
Safety-related system System that both
- performs the required safety functions that are necessary to achieve or maintain a safe
state for the EUC, and
- is intended to achieve the necessary safety integrity for the required safety functions on its
own or with other E/E/PE safety-related systems, safety-related systems of other
technology, or external equipment for risk reduction.
Safety instrumented system
(SIS)
Safety instrumented system to perform one or more safety-related functions. A SIS consists
of sensor(s), logic system, and actuator(s).
Lambda:
λ Failure rate per hour
Lambda Dangerous:
λ
D
Rate of dangerous failures per hour
Lambda Dangerous Detect:
λ
DD
Rate of detected dangerous failures per hour
Name Description
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