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A set of safeguards should work together to provide multiple layers of protection (Figure 1.7) designed to eliminate failures and mitigate the effect of machinery failures. Here is a list of generic safeguards that can be used as a starting point for a review. As you go down the list, the consequences increase in severity. For example, items 1 through 4 represent normal operation, items 5 and 6 go into action if an upset has occurred and some type of automatic action is required for correction, and finally, items 7 through 9 are required when a product release has occurred.

You must decide if this list makes sense in your situation.

1 Detailed operating procedures are recommended in all cases. There should be specific operating procedure for start-ups, shutdowns, and normal operations.

2 A set of operating targets for flow, pressure, and temperature limits help keep your equipment away from unsafe operating conditions

3 Reliable process control systemsFlow, pressure, and speed control

4 An alarm and operator Intervention planPeriodic walk-through inspectionsMachine alarms (temp, vibration, speed, etc.) to alert the operating of an unsafe condition

5 Safety Instrumented systems (SIS) for high consequence events, such as:Overspeed trip systemsTemp and vibration monitoring system set to tripAutomatic surge control

6 Physical ProtectionRelief valves for overpressure eventsElectrical breakersMechanical overspeed trips

7 At this point of our hypothetical scenario, there has been a full loss of containment. The potential released volume and flammability of the liquid or gas released will dictate the severity of the event. Physical containments can be used for mitigation, such as:Isolation valves (with fusible links) & battery limit valvesDikesDitchesBarriers and walls

8 If the severity of a release is deemed great enough then a plant emergency response plan may be required.

9 If the severity of a release is deemed great enough then a community emergency response may be required.

When it comes to safeguards, the following adage fittingly applies: Plan for the worst but hope for the best.