Risk Reduction - GE Mark VIe System Manual

2.2 Risk Reduction

Functional safety relates to proper equipment operation, as well as other risk reduction facilities. Layers of protection (LOP)
concepts are as follows:
The LOP around a process can be used to introduce risk reduction. Failure to carefully analyze the available LOP and the
likelihood-consequence relationship of the risks involved with process control failure can lead to an expensive over-design of
the system. The goal is to reduce the risk to a level that is as low as reasonably practicable (ALARP).
Residual
Residual
Risk
Risk
To achieve functional safety, it is necessary to analyze the potential hazards to personnel and property, including any
environmental impact, that could occur when the control of equipment is lost.
Requirements for safety function and integrity must be met to achieve functional safety. Safety function requirements describe
what the safety function does and is derived from the hazard analysis. The safety integrity requirement is a quantitative
measure of the likelihood that a safety function will perform its assigned task adequately. For safety functions to be
effectively identified and implemented, the system as a whole must be considered.
A primary parameter used in determining the risk reduction in a safety controller is the Average Probability of Failure on
Demand (PFD ). The inverse of the PFD
avg
Functional Safety
Plant Evacuation Procedures
Relief Valve
Mechanical Protection
Alarms with Operator Action
Safety Instrumented Systems
Process Alarms
Operator Supervision
Control and Monitoring
Prevention
Mitigation
Plant Emergency Response
Tolerable Tolerable
Risk
Risk
Necessary Risk Reduction
Actual Risk Reduction
Actual Risk Reduction
is the Risk Reduction Factor (RRF).
avg
RR-
F =
Public Information
Barrier
BPCS
Process
Necessary Risk Reduction
1
PFD
avg
Inherent
Inherent
Process
Process
Risk
Risk
Increasing Risk
GEH-6721_Vol_I_BP System Guide 69