Safety

Bulletin

U.S. Chemical Safety and Hazard Investigation Board

FIRE AT PRAXAIR ST. LOUIS

DANGERS OF PROPYLENE CYLINDERS IN HIGH TEMPERATURES

No. 2005-05-B|June 2006

St. Louis Facility

The St. Louis Praxair Distribution

site fills and distributes liquefied

and compressed gas cylinders,

rents welding machinery, and sells

welding supplies. At the St. Louis

facility, Praxair has about 30,000

compressed gas cylinders

containing oxygen, nitrogen,

propane, propylene, acetylene,

carbon dioxide, helium, and other

specialty gases onsite. The facility

employs about 70 and is located in

a commercial and residential area

near Lafayette Square.

When exposed to high temperatures and direct sunlight,

propylene cylinders can spontaneously vent through their

relief devices, in turn releasing propylene, which when

ignited, can heat surrounding cylinders and cause them to vent, creating

a domino effect that spreads the fire. This is what occurred on June 24,

2005 at Praxair’s gas filling and distribution facility in St. Louis,

Missouri. A small fire from one propylene cylinder spread to others and

then to propane and acetylene cylinders. Exploding cylinders flew up to

800 feet, damaged property, and started fires in the community. The fire

could not be extinguished until most of the flammable gas cylinders were

expended.

The U.S. Chemical Safety and Hazard Investigation Board (CSB) issues

this Safety Bulletin to focus attention on the propylene gas cylinder

hazards that contributed to the fire and explosions at the Praxair facility

and specific actions that propylene gas vendors can take to prevent

similar incidents, which include:

z Installing deluge systems or fixed fire nozzles to cool cylinders in case

of a fire;

z Providing barriers to limit fire spread; and

z Using flammable gas detectors in storage areas to provide early

detection of venting cylinders.

Summary Figure 1. Fire at Praxair St. Louis

Used by permission.

©MMV, CBS Broadcasting Inc.

All rights reserved.

z A small fire from one propylene cylinder

spread to others and then to propane and

acetylene cylinders. Exploding cylinders

flew up to 800 feet, damaged property, and

started fires in the community.
2

CSB Investigation Reports are

formal, detailed reports on

significant chemical accidents and

include key findings, root causes,

and safety recommendations. CSB Hazard

Investigations are broader studies

of significant chemical hazards. 

CSB Safety Bulletins are short,

general-interest

publications that

provide new or

noteworthy

information on

preventing chemical

accidents. CSB

Case Studies are short reports on

specific accidents and include a

discussion of relevant good

practices for prevention. All

reports include safety

recommendations when

appropriate. CSB Investigation

Digests are plain-language

summaries of Investigation

Reports.

Incident

Description

St. Louis was experiencing a heat

wave with bright sunlight and

temperatures reaching 97o

F (36oC)

on June 24, 2005. Praxair

operations proceeded normally

during the morning and early OFFICE

STORE

LAB

MACKAY AVE

CHOUTEAU AVE

PRODUCTION AREA

MISSOURI AVE.

Propane/Propylene Storage Area

N

Figure 2. Praxair Facility Layout Before the Incident.

Incident

afternoon; however, about 3:20 pm,

a technician retrieving cylinders

from an outside storage area saw a

ten-foot high flame coming from a

cylinder (Figure 3) and activated

the fire alarm. Security camera

video from the facility shows the

release and ignition of gas from a

cylinder in the propylene return

area.

[A]bout 3:20 pm, a

technician retrieving

cylinders from an

outside storage area

saw a ten-foot high

flame . . .

z

Praxair divided the cylinder

storage into “full” and “empty” or

“returned” sections. The

“returned” section, where the fire

originated, is for cylinders returned

for refilling, which may not always

be empty when returned.

s
3

Emergency

Response

The St. Louis Fire Department

arrived at about 3:35 pm; by this

time, a large number of flammable

gas cylinders were already

involved in the fire. With

explosions propelling cylinders in

all directions inside and outside

the facility, firefighters set up a fiveblock perimeter, evacuated local

residents, directed a water stream

on the fire, and extinguished

secondary fires started by cylinders

propelled offsite. The fire was

finally controlled at about 8:30 pm.

Community

Impact

Dozens of cylinders and cylinder

parts were propelled into the

community and were found on

sidewalks, front yards, backyards,

courtyards, parking lots, and under

cars. Damage included a burnedFigure 4. Spreading Fire (three minutes after ignition)

Figure 3. Initiating Event (from Praxair security camera)

As workers and customers

evacuated, the fire spread to

adjacent cylinders. Security camera

video shows nearby cylinders

igniting in the first minute. At 2

minutes, cylinders begin

exploding, flying into other areas of

the facility, and spreading the fire

(Figure 4). After 4 minutes, the fire

covers most of the facility’s

flammable gas cylinder area and

explosions are frequent.

With explosions propelling cylinders in all

directions . . . firefighters set up a five-block

perimeter, evacuated local residents, directed a

water stream . . .

z
4

Figure 5. Community Impact
5

1 Acetylene cylinders are filled with a

porous solid material, which in older

cylinders, may contain asbestos.

2 Following the incident Praxair

contracted a cleanup of the asbestos

which the Missouri Department of

Natural Resources monitored.

3 From report of the St. Louis Medical

Examiner, Case Number 2005-2061.

out empty commercial building,

fire-damaged cars, a three-foot hole

in the wall of one residential

building, broken windows, and

other destruction to residential and

commercial buildings. Cylinder

parts traveled as far as 800 feet

from the area of the explosions

(Figure 5). The fire plume spread

asbestos1 from ruptured acetylene

cylinders over a 1/3-mile wide and

1-mile long area.2

The St. Louis Chief Medical

Examiner attributed the death of

one St. Louis resident to an asthma

attack triggered by noxious smoke

and fumes from the incident.3

Facility Damage

While the facility was damaged

extensively by fire and water, 22

employees and two customers

evacuated safely in accordance

with Praxair’s procedures. A

corner of the main production

building and store area was

heavily fire-damaged. Inside, the

office and store areas were waterand smoke-damaged. In all, the fire

consumed nearly the entire

inventory of flammable gas, or

about 8,000 cylinders (Figure 6).

Figure 6. Facility Damage

Incident

Analysis

Incident Scenario

The CSB used physical evidence,

surveillance video recording,

interviews, and information from

Praxair’s internal investigation to

establish the likely failure

sequence:

z Direct sunlight and radiant heat

from asphalt paving heated

returned propylene cylinders;

z High ambient temperature

limited natural air-cooling of the

cylinders;

z The returned cylinders,

containing less gas than full

cylinders, heated at a faster rate

than full cylinders;

z As the cylinder wall

temperatures rose, the internal

pressures increased causing the

relief device on a cylinder valve

to open and vent propylene;

z The venting propylene ignited

(most likely from a static

discharge) at about 3:20 pm;

z An adjacent cylinder, further

heated by the fire, released

propylene, and caught fire;

z An employee saw the fire and

activated the fire alarm;
6

4 Liquefied petroleum gases (LPGs) are

gases that are liquefied by applying

pressure. Common LPGs include butane,

propane, and propylene.

5 A majority of the cylinders that ejected

from the site were acetylene cylinders.

6 Air temperature data from the nearest

National Weather Service reporting

station.

7

 Identified in the fire department or

company investigation report.

z All 22 employees and two

customers evacuated;

z The growing fire heated

additional cylinders, which

released more propylene into the

fire;

z The fire’s intensity continued to

raise cylinder temperatures,

softening the steel and rupturing

the cylinders;

z The fire spread to a group of

acetylene cylinders;

z The liquefied petroleum gas4

(LPG) area of the facility became

fully involved in the fire;

z Ruptured cylinders (acetylene,

propane, and propylene)

rocketed into the community,

damaging buildings and starting

several vehicle fires;5

z St. Louis Fire Department

arrived at about 3:35 pm,

established an unmanned water

spray on the fire, and retreated to

a safe distance. The fire

department did not actively fight

the main fire due to the danger of

rocketing cylinders;

z The Fire Department gained

control of the fire at about 8:30

pm, after the fire had consumed

most of the flammable gases

onsite.

Similar Incidents

CSB found three recent incidents

similar to the St. Louis fire. They

include:

z Air Liquide, Phoenix, Arizona –

June 1997;

z Airgas, Tulsa, Oklahoma –

August 2003; and

z Praxair, Fresno, California – July

2005.

These events occurred in gas

repackaging cylinder fill plants on

days with air temperatures above

100oF (37oC)6 and in an area with

propylene cylinders.7

On June 18, 1997, air temperatures

in Phoenix, Arizona reached 108o

F

(42oC). At about 4:30 pm,

propylene was released from

cylinders and/or tanks at an Air

Liquide gas repackaging plant;

moments later, the propylene

ignited. The fire spread to adjacent

cylinders, followed by explosions

that further damaged the facility.

Investigation reports concluded

that the incident resulted from the

release of propylene close to LPG

cylinders and bulk tanks and that

high temperature was a

contributing factor.

On August 18, 2003 air

temperatures reached 100oF (37oC)

in Tulsa, Oklahoma. At about 4:30

pm, a vapor cloud of propylene

that had formed around cylinders

in the yard ignited, spreading fire

around the Airgas gas distribution

plant. As in the St Louis incident,

cylinders exploded and flew into

the community, damaging cars and

homes (see Figure 7). Tulsa Fire

Department investigators

Figure 7. Tulsa Damage

Photo courtesy of Tulsa Fire Department
7

8 The propane industry estimates that 50

million propane cylinders are in use

nationwide. CSB has estimated that the

number of propylene cylinders in use is

about 50,000.

9 Vapor pressure is the pressure exerted

by a vapor in equilibrium with its solid or

liquid phase.

10Cylinder standards can be found 49 CFR

part 173.

11The DOT standards exempt users from

complying with paragraph 9.1.1 of CGA

pamphlet S-1.1, which requires that relief

valves be replaced or recertified every 10

years.

50

100

150

200

250

300

350

400

450

500

50 60 70 80 90 100 110 120 130 140 150 160

Temperature, degrees F

Vapor pressure, psig

Propane Vapor Pressure Propylene Vapor Pressure

Propane Minimum Relief Setpoint Propylene Minimum Relief Setpoint

 Figure 8. Propane and Propylene Vapor Pressures

Following several of the fires

described, including the St. Louis

fire, the affected companies

investigated the performance of the

propylene cylinders CG-7 relief

valves. In 2003, Battelle12 released

a report, “Testing and Assessment

of CG-7 Pressure Relief Valve and

Propane Cylinder Performance”

that documented the results of a

study it performed for the National

Propane Gas Association. The

companies’ investigations and the

12Battelle is a non-profit global science

and technology enterprise that develops

and commercializes technology and

manages several national laboratories for

the U.S. Government.

concluded that although the

official cause is undetermined, the

most likely cause was “propylene

venting due to the prolonged

exposure to excessive heat.”

Comparing

Propylene and

Propane

This safety bulletin describes several gas repackaging facility fires

that likely began with a spontaneous propylene release, similar to

the fire in St. Louis, and that occurred since 1996. Although about

1,000 times more propane cylinders are in service than are propylene cylinders,8

 CSB found gas repackaging facility fires that began

with a propane release do not occur with significantly greater frequency. To understand why, CSB

compared propylene and propane

cylinder characteristics.

Propylene and propane have

similar physical properties; both

are liquefied petroleum gases and

use the same cylinders and relief

device standards. A physical

property, known as the vapor

pressure,9 determines pressure in

the cylinder.

Propylene and propane cylinders

are manufactured to U. S.

Department of Transportation

(DOT) standards.10 The DOT

standards require that each

cylinder be equipped with a

pressure relief device that meets the

requirements of Compressed Gas

Association, Inc. (CGA) Pamphlet

S-1.1, “Pressure Relief Device

Standards – Part 1 – Cylinders for

Compressed Gases, 2001, Ninth

Edition.”11 CGA Pamphlet S-1.1

specifies a CG-7 type relief valve for

both propylene and propane

cylinders. Pamphlet S-1.1 also

specifies the set point of the relief

valve. Figure 8 shows the vapor

pressure curves and minimum

relief valve setpoints for propylene

and propane.
8

Best Practices for

Cylinder Storage

National Fire Codes, CGA’s “Safe

Handling of Compressed Gases in

Containers,” and company

standards provide general

guidelines for storing cylinders

outdoors:

z Ensure the pressure relief valve

is in direct communication with

the vapor space;

z Use a well-ventilated area away

from oxidizers, open flames,

sparks, etc.;

z Post “No-Smoking” signs;

z Post hazard class or name of

gases on containers;

z Group by hazard class;

z Protect from objects that will

damage the metal surface—not

near elevators, walkways,

platform edges, or below heavy

moving objects that may fall;

z Protect from tampering;

 Propylene Propane

Pressure, Temperature, Pressure, Temperature,

psig oF psig oF

Cylinder Service Pressure 260 115 240 124

Minimum Relief Setpoint 390 149 360 158

Table 1. Pressures and Temperatures

for LPG Cylinders

As Table 1 shows, propylene relief

valves may open at lower

temperatures than propane.

z Avoid prolonged exposure to a

damp environment (graded

surface prevents water

accumulation); and

z Do not obstruct exit routes.

Three additional best practices are

relevant to the incidents discussed

in this safety bulletin that gas

repackaging facilities should

evaluate and implement as

appropriate: fire mitigation, fire

barriers, and gas detection.

Fire Mitigation

Exploding and rocketing cylinders

put fire fighters at risk when

attempting to extinguish a gas

repackaging plant fire. Fixed fire

protection such as fire monitors,

deluge, or sprinkler systems can

immediately cool cylinders

reducing the likelihood of

additional cylinder releases, fire

spread, and off-site consequences.

Fire Barriers

Using barriers in storage areas can

contain exploding cylinders and

limit the spread of the fire in the

first critical minutes before

firefighters arrive.

Gas Detection

Area flammable gas monitors can

detect releases. Detection of

flammable gases may allow safety

systems (such as alarms and

deluge) to activate before ignition,

reducing the likelihood of

uncontrolled fires.

Battelle report document variability

in the opening pressure of relief

valves in service, which found that

a significant number open below

the minimum pressure required by

CGA pamphlet S-1.1. One

company study and the Battelle

report document a decrease in set

pressure for subsequent valve

openings after the initial opening.

Although the performance of the

CG-7 relief valves appears to be

similar for propylene and propane,

spontaneous releases leading to

large facility fires have occurred

primarily with propylene even

though about 1,000 times more

propane cylinders are in service

than propylene cylinders. The

propylene fires can be attributed to

the greater margin provided in

standard propane cylinders

between the vapor pressure of

propane and the minimum set

pressure of the relief valve. Table 1

lists the temperature for various

pressures in both propylene and

propane cylinders.
9

Revising current

practices to provide a

greater margin

between the minimum

relief opening pressure

and the vapor pressure

of propylene will

reduce the risk even

when best practices are

not followed.

Lesson

Learned

The lesson learned from these fires

can help similar facilities avoid

damaging incidents. High ambient

temperatures, in combination with low

relief valve opening pressure, increase

the risk of catastrophic fires at facilities

handling propylene cylinders.

Adopting best practices for storing

and handling propylene cylinders

can reduce this risk at gas

distribution facilities. Revising

current practices to provide a

greater margin between the

minimum relief opening pressure

and the vapor pressure of

propylene will reduce the risk even

when best practices are not

followed.

Recommendations

Compressed Gas

Association (CGA)

2005-I-MO-R1

Communicate with your

members who operate gas

repackaging facilities the details

of this incident and the best

practices for handling and

storing cylinders.

2005-I-MO-R2

Revise CGA standards for the

CG-7 relief valves used in

propylene service to require:

1) a greater margin between

vapor pressure and relief valve

setpoint (similar to propane);

and

2) that valves be capable of

multiple operations within the

specified setpoint tolerance or be

furnished with an indicator that

alerts users that the valve has

operated.

High ambient z

temperatures, in

combination with low

relief valve opening

pressure, increase the

risk of catastrophic

fires at facilities

handling propylene

cylinders.

z
10

References

Britton, Laurence G, 1999.

Avoiding Static Ignition Hazards in

Chemical Operations, Center for

Chemical Process Safety,

American Institute of Chemical

Engineers (AIChE), New York,

1999.

Compressed Gas Association

(CGA), 2000. Safe Handling of

Compressed Gases in Containers

(9th edition). Chantilly, VA:

CGA.

Compressed Gas Association,

2005. Pressure Relief Device

Standards – Part 1 – Cylinders for

Compressed Gases, 2001,

Pamphlet S-1.1, (12th edition),

Chantilly, VA: CGA.

Department of Transportation

(DOT), 49 CFR Subchapter C,

Hazardous Materials

Regulations.

CSB publications may be downloaded at www.csb.gov or obtained by contacting:

The U.S. Chemical Safety and Hazard Investigation Board (CSB) is an independent Federal agency whose mission is to ensure

the safety of workers, the public, and the environment by investigating and preventing chemical incidents. CSB is a scientific

investigative organization; it is not an enforcement or regulatory body. Established by the Clean Air Act Amendments of

1990, CSB is responsible for determining the root and contributing causes of accidents, issuing safety recommendations, and

studying chemical safety issues.

No part of the conclusions, findings, or recommendations of CSB relating to any chemical incident may be admitted as

evidence or used in any action or suit for damages arising out of any matter mentioned in an investigation report (see 42

U.S.C. § 7412(r)(6)(G)). CSB makes public its actions and decisions through investigation reports, summary reports, safety

bulletins, safety recommendations, case studies, incident digests, special technical publications, and statistical reviews. More

information about CSB may be found at www.csb.gov.

U.S. Chemical Safety and Hazard Investigation Board

Office of Congressional, Public, and Board Affairs

2175 K Street NW, Suite 400

Washington, DC 20037-1848

(202) 261-7600

International Code Council (ICC),

2003, International Fire Code,

Falls Church, VA, ICC

Lemoff, Theodore C. (ed.), 1998. 

Liquefied Petroleum Gas Code

Handbook (5th edition), Quincy,

MA: NFPA.

Occupational Safety and Health

Administration (OSHA), 29 CFR

part 1910, subpart H, Hazardous

Materials.

Praxair Technology, Inc., 2006.

“About Praxair,” http://

www.praxair.com,

April 17, 2006.

Stephens, D.R. et al., 2003. Testing

and Assessment of CG-7

Pressure Relief Valve and

Propane Cylinder Performance,

Vol. 1, Columbus, OH: Battelle.

Western Fire Chiefs Association,

2000, Uniform Fire Code,

Fallbrook, CA, Western Fire

Chiefs Association