Process Safety

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http://dx.doi.org/10.1016/j.jchas.2

Learning from exp

erience revisited

I n March/April 2008, this column wasabout ‘‘Learning from Experience’’.1 Sixyears later, recent experience makes this

topic worth revisiting. I have been using a USChemical Safety Board (CSB) video of a fire at aPraxair gas distribution facility in St. Louis, MO20052 in process safety courses. The audience isgenerally not involved handling flammable,compressed gas cylinders. I ask students, beforeshowing the video, to think about why we areshowing it, and what lessons from this incidentapply to their facilities. There is a lot to learnfrom this incident for any facility.

To briefly summarize the incident, June 24,2005 was a hot day, up to 97 8F, in St. Louis.About 3 PM, a fire was seen in the ‘‘empty’’propylene cylinder (unlikely to really be com-pletely empty) storage area. The fire is believedto have been caused by the opening of a reliefvalve on a propylene cylinder due to the vaporpressure of propylene, perhaps at a pressurebelow its set point. The vapor pressure of pro-pylene equals the 390 psig relief valve set pres-sure at 149 8F. The fire rapidly escalated, andwithin minutes involved the entire facility.Employees immediately evacuated and calledfor assistance from the St. Louis fire depart-ment. The fire department evacuated peoplefrom a 5 block area surrounding the facility andfocused on preventing spread of the fire. Therocketing cylinders made it too dangerous toapproach the fire too closely.

A number of lessons from this incident applyto almost any process facility.

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fire can escalate very quickly, and rapidaction is necessary to protect people whowork in the facility. The CSB reports thatwithin 4 minutes of the fire first beingobserved, most of the facility was involvedand cylinders were already observed to beexploding frequently!

� T he Praxair employees did the right thing –

they evacuated the plant and called for help.The fire department also did the right thingand focused on protecting people from theeffects of the fire. This is in contrast to otherincidents where employees tried to respond

endershot, D. C. Learning from Experience.Chem. Health Safety, 2008, 15 (2 (March/pril), 34–35.ttp://www.csb.gov/praxair-flammable-gas-linder-fire/ (accessed 8.3.14).

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to an incident and stop a release of flam-mable or reactive material, and were killed inan explosion when their efforts failed.3

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lthough it may have opened prematurely,the relief valve likely did what it was sup-posed to do – it prevented rupture of thecylinder to which it was attached. The fireresulted from ignition of the discharge fromthe relief valve. Emergency relief is a system,including understanding what happens tothe material released. This may be difficultto manage for a portable cylinder, but in afixed process facility you have control overwhat happens to a relief device discharge.

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elief valve performance can deteriorate fol-lowing activation.

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robust process with a larger differencebetween normal operating pressure (as wellas foreseeable deviations) and the relief valveset pressure is inherently safer. The CSBvideo narration indicates that the relief valveon the cylinder could have been set at ahigher pressure – the cylinders were strongenough to withstand greater pressure. Thismay be true for the cylinders involved in theincident, but perhaps not for all propylenecylinders. This doesn’t only apply to pres-sure, but to any safety-critical process para-meter – you don’t want normal operatingconditions to be too close to a hazardouscondition.

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here is a ‘‘learning from experience’’ lessonin this incident. The CSB report identifiestwo similar incidents that had occurred atother places, in 1997 in Phoenix, AZ, and in2003 in Tulsa, OK, both involving propylenecylinders and hot weather. About a monthafter the St. Louis incident, another Praxairfacility in Fresno, CA had a similar incident.

When reading incident reports and viewingsafety videos such as those from the CSB, oneof your challenges is to understand how youcan apply the lessons to your process, eventhough the technology may be very differentfrom that involved in the incident.

or example, the CSB report on the April 2004plosion at a PVC plant in Illiopolis, IL (http://ww.csb.gov/formosa-plastics-vinyl-chloride-plosion/), and the EPA/OSHA report on anplosion in a blender in Lodi, NJ in April95 (http://www.epa.gov/oem/docs/chem/pp.pdf).

Health and Safety of the American Chemical Society 35Elsevier Inc. All rights reserved.