Suppose that in a hazardous scenario a high pressure separator releases liquid to downstream equipment. If the liquid level in the high pressure separator decreases to a certain level, pressure could be released to downstream equipment and cause it to rupture. In this scenario, a controller monitors the liquid level. If the level gets too low, the controller closes a valve so that the pressure is not released to downstream equipment.
An independent layer of protection for this scenario would be a low level alarm because it meets all the following criteria:
- The safeguard is independent because if the first controller fails, the low level alarm has independent process connections and independent BPCS hardware from the failed controller.
- The safeguard is auditable because the low level alarm can be routinely inspected.
- The safeguard is capable because it is available at least 90 percent of the time.
- The safeguard is specific because the alarm detects potential hazards by measuring the liquid level and will alert the operator when the potential failure is detected.
- The safeguard increases the Risk Reduction Factor (RRF) to a value greater than or equal to 10.
Therefore, the level alarm along with an operator response can reduce the risk associated with the hazards scenario.