Page 6 - Temporary Isolation of Relief Devices - CCPS Safe Work Practice

Need/Call To Action

Temporary isolation of PRDs on operating processes is a manual activity; therefore, safe, and successful isolation
is directly related to a site’s Operational Discipline. The work process of temporarily isolating PRDs is interrelated
with Permit to Work, Management of Change, Locked Valve, and Pre-startup Safety Review (PSSR) procedures. Two
incidents are presented in which loss of containment due to vessel rupture occurred after the relief devices on the
vessels were manually isolated.
Incidents Continue To Happen

“In March 1969, a liquid carbon dioxide storage tank located at a steel mill in Fukushima, Japan catastrophically
ruptured causing three fatalities and 38 injuries. The incident investigation revealed that repair work for the liquefied
carbon dioxide storage tank was being carried out at the time. Before the accident, the isolation valve under the main
safety valve was closed while liquid remained in the tank. In addition, the tank’s heating system was still operational. A
boiling liquid, expanding vapor explosion (BLEVE) of liquid carbon dioxide occurred due to the rapid pressure release.”
Liquid CO2 Tank Rupture (1969)

“In June 2005, a liquid nitrogen trailer parked at a cryogenic air separation plant in Taiwan catastrophically ruptured.
The trailer arrived at the plant site with a residual quantity of about 7 tons of liquid nitrogen and was venting due to an
abnormally high pressure, possibly because of poor vacuum in its insulated space. The driver deliberately closed the
inlet isolation valve under the main pressure safety valve on the trailer during the night shift to avoid gas venting noise
at night. The overpressure rupture occurred the following morning. After the accident, the trailer’s main pressure safety
valve was tested and determined to function properly.”
Taiwan COLA 2009 Publication
Lapses in Operational Discipline Continue to Happen

As discussed above, Operational Discipline is a contributing factor to incidents involving relief device isolation.
The data presented below illustrates a continued opportunity for operating facilities to improve in this aspect of
safe plant operation.

“ According to investigations on industrial accidents, human errors account for > 90% of accidents in
nuclear industries, > 80% of accidents in chemical industries, > 75% of maritime accidents, and > 70%
of aviation accidents.” Journal of Loss Prevention in the Process Industries 2012

“ Two-thirds of all accidents in the chemical industry were related to maintenance and failure of Permit to
Work (PTW) was the single largest cause. As such, work permits play a key role in ensuring a safe working
environment and minimizing human error. In many cases, it was analyzed that there was negligence because
the risk assessment was omitted to carry out dangerous work, and the work permit was not issued during
hazardous work.” International Journal of Environmental Research and Public Health 2021

“ Statistics on the accident cases published by the Chemical Safety and Hazard Investigation Board (US), the
European Major Accident Reporting System, and in the Failure Knowledge Database (Japan) has revealed that
Permit to Work (PTW) has significant contribution to the occurrence of accidents and is worthwhile to be studied in
detail. Failure in complying with the PTW system has caused major accident cases, such as Motiva Enterprise LLC
(2001), Phillips Pasadena (1989), and Piper Alpha Platform (1988). Another reason for studying PTW is that the trend
of its percentage of contribution to process accident rates is not decreasing over the past two decades even though
there is shared information and feedback available.” Chemical Engineering Transactions 2017

3 SAFE WORK PRACTICE, TEMPORARY ISOLATION OF RELIEF DEVICES