Safety

Bulletin

U.S. Chemical Safety and Hazard Investigation Board

REMOVAL OF HAZARDOUS MATERIAL FROM PIPING SYSTEMS

No. 2004-03-B | July 2004

Chemical and refinery facility personnel open piping and equipment to perform routine maintenance, add/replace components, or

modify pipe routing. The piping may contain hazardous material, such

as flammable hydrocarbons, toxic chemicals, or thermally reactive

chemicals. Safe work practices dictate the removal or mechanical

isolation of hazardous material from piping and equipment (e.g., using

valves or blind flanges) before commencing work.

This Safety Bulletin identifies specific tasks that facilities should

include in all work activities involving piping or equipment opening to

ensure the complete removal of hazardous material. In addition,

guidance is provided on implementing generic (plant-wide) procedures

for nonroutine work activities.

Introduction

Peroxide

Explosion and

Flash Fire

In January 2004, the U.S. Chemical

Safety and Hazard Investigation

Board (CSB) investigated an

explosion and fire at a Huntsman

Petrochemical Corporation facility

in Port Neches, Texas. During a

steam purge for a piping modification that required line opening

and hot work (i.e., cutting and

welding), a peroxide/alcohol

mixture was heated above its

thermal decomposition temperature. The mixture was trapped in a

low point along a 900-foot-long,

6-inch process pipe. The resulting

explosion and fire seriously injured

two employees.

Plant personnel incorrectly

believed that a nitrogen gas purge

preceding the steam purge had

removed all liquid from the pipe.

However, an unknown quantity of

a thermally reactive peroxide/

alcohol mixture remained in an

unidentified low-point trap in the

pipe.

As the steam heated the trapped

peroxide, it exothermically

decomposed and overpressurized

the pipe, causing it to rupture

(Figure 1).

The venting flammable vapor then

ignited, resulting in a flash fire that

burned two employees and

significantly damaged nearby

equipment (Figure 2). The

automatic deluge system and the

fire brigade suppressed the fire.

Incident Causes

Incomplete Removal of

Hazardous Mixture

Huntsman operating and

maintenance procedures

highlighted the hazards of

incomplete removal of toxic,

flammable, or reactive chemicals

from pipes and equipment. The

normal unit startup procedure

required clearing the peroxide/

alcohol from the line using a

nitrogen gas purge.

Plant personnel were aware of the

hazards associated with leaving

peroxide in a closed piping system.

However, the procedural steps for

the nitrogen gas purge were

 Figure 1. Ruptured pipe/valve

and fire damage.
2

CSB Safety Bulletins offer advisory

information on good practices for

managing chemical process hazards.

Case studies provide supporting

information. Safety Bulletins differ

from CSB Investigation Reports in

that they do not comprehensively

review all the causes of an incident.

U.S. Chemical Safety and Hazard

Investigation Board

Office of Investigations and Safety

Programs

2175 K Street NW, Suite 400

Washington, DC 20037-1848

202-261-7600

www.csb.gov

ineffective in removing all of the

hazardous mixture from the pipe.

The modification work order for the

infrequently used startup line

required hot work on the pipe; it

included a nitrogen purge before

opening the line, similar to the

normal line clearing procedure.

This activity was intended to clear

thermally reactive liquids from the

line prior to steam purging to

remove all traces of flammable

material. Steam purging was a

prerequisite to performing hot work

on any piping or equipment.

The pipe routing contained a lowpoint segment almost 300 feet long

(Figure 3), with a volume in excess

of 350 gallons. The pipe was

routed more than 20 feet aboveground in an overhead pipe rack

that obscured the long, shallow

low-point section (Figure 4).

Operators were unaware that the

nitrogen gas purging, required by

the operating procedure, was

ineffective in removing all of the

peroxide/alcohol mixture in the

low point. Preparing the line for

hot work required an additional

nitrogen purge as a precaution,

then the steam purge to complete

the removal of residual hydrocarbon vapor. This was the first

time hot work had been specified

for this line.

It was only when the pipe was

purged with steam in preparation

for the approved pipe modification

that the peroxide overheated,

causing it to decompose and overpressurize the pipe.

Inadequate Verification of

Pipe Routing

The liquid could have been safely

removed before the steam purge.

As shown in Figure 3, both ends of

the long pipe section contained

low-point drains.

A comprehensive review of the asbuilt drawings, combined with a

walkdown of the entire peroxide/

alcohol transfer pipe—if required

in the management of change

(MOC) process—would have likely

identified the low-point trap.

Although the low-point piping

segment and two available drains

were shown on the as-built piping

isometrics, the low point was split

onto separate sheets (Figure 3),

 Figure 2. Floor stanchion and

piping tangled in damaged

overhead electrical conduits.

 Figure 3. Unused low-point drains on piping segment.

3 ft

As-built 

isometric 2

300 ft

As-built 

isometric 1
3

making it difficult to recognize the

liquid trap. Furthermore, the

piping modification involved only

one of the isometric drawings.

As in most large chemical manufacturing facilities, many miles of

piping were routed throughout

overhead pipe racks (Figure 4).

There is a high probability that

some low points will be overlooked unless a pipe walkdown

focuses on identifying both low

points and installed drains.*

Unsafe Heating of

Thermally Sensitive

Chemicals

Using the generic steam purging

procedure on the peroxide/alcohol

pipe created an unanticipated

hazard. The steam temperature

exceeded 380oF, which is significantly above the decomposition

temperature of the peroxide.

The hightemperature steam

flowed through

the piping system

for nearly 1.5

hours, and the

trapped peroxide

began to decompose. Pressure

buildup ultimately

caused a valve

gasket to fail and

release flammable

vapor.

At about the same

time, the pipe

upstream of the leaking valve burst,

releasing additional flammable

liquid and vapor, further spreading

the fire. The pressure concussion

also caused additional damage to

equipment in the area.

Inadequate Hazards

Review of Procedure

Revision

Complex pipe routing and

equipment configurations often

contain low points that trap

hazardous material. Flushing the

pipe with water or other suitable

liquid may effectively remove the

material but generates a significant

quantity of waste liquid. Furthermore, liquid that remains in low

points or equipment may cause

unsafe conditions or degrade

piping.

To reduce waste volume,

Huntsman revised the procedures

to substitute inert gas purging for

water flushing. However, purging

with inert gas or steam does not

necessarily remove trapped liquid.

The revised procedure:

Failed to address the importance

of identifying low points in the

piping.

Failed to require the use of lowpoint drains to remove trapped

hazardous liquids.

Proper identification and use of

drains ensures the complete

removal of hazardous liquids.

The revised inert gas purging

procedure was applied to process

pipes containing thermally

unstable liquids without

adequately considering the

hazards if these liquids remained

in the pipe during the steam purge.

High-temperature steam—used to

remove traces of flammable vapor

from the pipe prior to performing

hot work—may cause thermally

unstable liquids to violently

decompose. This is precisely what

occurred with the peroxide/

alcohol mixture in this incident.

Lessons Learned

Nonroutine Pipe and

Equipment Opening

Opening chemical process piping

and equipment can be extremely

hazardous. It should never be

considered routine work.

Facilities handling hazardous

chemicals should:

Perform a complete walkdown of

all piping and components

between the isolation devices.

Update as-built drawings as

necessary.

*After the incident, Huntsman

conducted a comprehensive walkdown

of all peroxide piping and identified

additional low-point traps. An MOC

work order was implemented to

eliminate each trap.

 Figure 4. Piping and electrical conduits in congested,

overhead pipe rack.
4

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, studying chemical safety issues, and evaluating the effectiveness of other government

agencies involved in chemical safety.

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.

CSB investigation reports may be purchased from:

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5285 Port Royal Road

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For international orders, see:

www.ntis.gov/support/cooperat.htm.

CSB publications may be downloaded at www.csb.gov or

obtained by contacting:

U.S. Chemical Safety and Hazard Investigation Board

Office of Government, Public, and Board Affairs

2175 K Street NW, Suite 400

Washington, DC 20037-1848

(202) 261-7600

Use as-built drawings of the

affected piping to identify all

branch connections, isolation

valves, low-point drains, and

high-point vents.

Prepare a specific written

procedure for removing,

flushing, and purging

hazardous material from the

system. Consider the

consequences if flushing liquid

remains in the system after the

work is complete.

Unit-Specific Procedures

Unit-specific procedures should be

used to ensure the safe conduct of

nonroutine activities, such as

steam purging of process lines that

handle thermally unstable liquids.

Facilities should:

Review planned steps against

unit-specific hazards.

Update unit-specific procedures

as necessary to address unique

characteristics of the activity,

especially when modifications

are involved.

If a modification activity

includes the use of generic safety

procedures, clearly identify

applicable constraints (e.g.,

specify additional inspection

steps to verify removal of all

energy sources, including

thermally reactive chemicals).

For Further

Reading

U.S. Chemical Safety and Hazard

Investigation Board (USCSB),

2002. Hazard Investigation,

Improving Reactive Hazard

Management, Report No. 2001-01-

H, December 2002.

USCSB, 2002. Investigation Report,

Steel Manufacturing Incident,

Bethlehem Steel Corporation, Burns

Harbor Division, Chesterton,

Indiana, February 2, 2001, Report

No. 2001-02-I-IN, January 2002.

USCSB, 2002. Investigation Report,

Thermal Decomposition Incident,

BP Amoco Polymers, Inc., Augusta,

Georgia, March 13, 2001, Report

No. 2001-03-I-GA, June 2002.

USCSB, 2001. Investigation Report,

Refinery Fire Incident, Tosco Avon

Refinery, Martinez, California,

February 23, 1999, Report No. 99-

014-I-CA, March 2001.