Page 9 - Temporary Isolation of Relief Devices - CCPS Safe Work Practice

Potential Hazardous Consequences

EQUIPMENT OVERPRESSURE CAUSED BY LIMITED RELIEF CAPACITY DUE
TO ISOLATION

An operational upset during PRD isolation with limited or no relief capacity can severely challenge the design envelope
of pressure equipment, resulting in a catastrophic failure. Refer to the Major Incidents section at the end of this SWP
where operational upsets during PRD isolation caused catastrophic accidents.

Personnel Injury

There are three main causes of injury and damage from pressure equipment catastrophic failure:
g The most common cause is a pressure (“blast”) wave that radiates from the explosion epicenter. The pressure wave
can cause serious injury or fatality to both outdoor personnel and personnel in buildings not designed to withstand
the blast force.
g Thermal radiation from combustion of a flammable material release.
g Projectiles, such as flying metal, glass, or wood, created by the explosion.

Property Damage From Fire or Explosion

The blast wave can cause the secondary failure of other nearby process equipment (i.e., “cascade” or “domino” event)
and the release of the contents from that equipment. Cascade events releasing flammable materials can cause fires and
explosions (if ignition sources are available) that often result in significant plant-wide damage causing business disruption.

Chemical Release and Community Impact

The blast wave from a large vessel failure can travel off-site causing damage or destruction of neighboring buildings. In
addition, the release of large quantities of flammable or toxic materials from the primary or secondary failure of equipment
can cause community impact requiring evacuation or Shelter-in-Place.

SAFE WORK PRACTICE, TEMPORARY ISOLATION OF RELIEF DEVICES 6