Learning from Experience

Second Pamphlet

GEST / AP 2
October 1999
 GEST / AP 2

TABLE OF CONTENTS
INTRODUCTION 3

I. LIQUID CHLORINE UNLOADING: RUPTURE OF A FLEXIBLE PTFE

HOSE 4

II. BACK-FLOW OF CHLORINE INTO INSTRUMENT AIR NETWORK 6

III. LIQUID CHLORINE LEAK AFTER PUMP START-UP 8

IV. NCL3 EXPLOSION AS A RESULT OF BRINE CONTAMINATION WITH

UREA 10

V. PLANT START-UP AFTER MAINTENANCE : CHLORINE EMISSION

DUE TO HUMAN ERRORS 12

VI. CHLORINE EMISSION AT THE START-UP OF AN INSTALLED SPARE

GAS BLOWER 14

VII. LESSONS FROM AN ACCIDENT IN A NON-EUROPEAN WATER PLANT 17

VIII. LEAK ON A PUMP ASSOCIATED WITH A LIQUID CHLORINE

STORAGE 20

IX. LEAK IN A 500 KG DRUM IN AN AIRPORT FACILITY 23

Documents included

1. Flow chart illustrating the way Euro Chlor works within the concept of
"Responsible Care" 22

2. Fatal accident analysis (Euro Chlor and rest of the world) 23

3. Fatal accidents as a function of time and of chlorine production 24

4. Fatal accidents by activity 26

5. Major causes of all accidents involving chlorine 30

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INTRODUCTION

The Euro Chlor General Technical Committee is committed to improving the safety of
chlorine production and distribution. Accidents are analysed and discussed within the
GEST Committee. On a periodic basis, a brochure is published outlining significant
chlorine accidents which have happened during the preceding period. Although some
statistical data may be included, the main purpose is to identify the lessons to be learnt
from the accidents, so that they can be prevented in other plants. The objective, very
simply, is LEARNING FROM ACCIDENTS.

Accidents are included, not necessarily because there have been serious
consequences, but because there are important lessons to be learnt. The
circumstances and causes of each accident are described in as much detail as is
helpful. Any issues concerning compliance, or non-compliance, with Euro Chlor
recommendations are highlighted. If appropriate, Euro Chlor recommendations will be
revised to take account of the lessons. Any improvement, either to procedures or to
equipment, will also be included.

Euro Chlor welcomes comments and criticism, to improve the value of the publication
to the industry.

The pamphlet is another application of the Responsible Care commitment of the Euro
Chlor Federation and all its members.

In this edition, a historical record of fatal accidents over the last 45 years is given.

Although, Euro Chlor has an extensive and growing record of accidents and incidents,
the comprehensiveness of these is dependent on the quality of the reporting and in
earlier times, this may not have been complete. However, Euro Chlor is fairly confident
of the fatal accident records and believes that these demonstrate a real improvement
in safety performance of the industry.

October 1999 Page 3 of 34

 GEST / AP 2

I. LIQUID CHLORINE UNLOADING: RUPTURE OF A FLEXIBLE

PTFE HOSE

Introduction

The accident reported here happened a few years ago at a large chlorine consumer's
premises. It is a good example of how non-application of Euro Chlor recommendations
can lead to potentially serious consequences. It shows how the correct application of
Euro Chlor recommendations can prevent accidents.

Process Description

The unloading station was contained in a small building. 25 tonnes chlorine rail tanks
were unloaded by air padding at 8 barg pressure. The flexible hose used was a 25 mm
diameter PTFE hose braided with stainless steel wires. The pneumatic valves on the
rail tanks were not connected to the instrument air. Limited means of abatement
existed in the event of a chlorine escape in the building. Water sprinklers were
installed within the building and at the inlet of a chimney. The water could be replaced
by a caustic soda solution.

Circumstances of the Accident

During unloading, the hose failed catastrophically. A large amount of chlorine flooded
to the ground. It was impossible to close the valves automatically or at a distance with
push buttons. The concentration of chlorine in the building made it impossible to have
quick access to the rail tanker valve.

It took 20 minutes before personnel wearing full protective equipment could enter the
building and close the valve by hand.

10 tonnes of chlorine escaped and more than 200 people were injured in the
immediate vicinity of the building.

Learning from the Accident

 Use of a PTFE hose

This material, for use on liquid chlorine, is definitely not recommended by Euro Chlor
because many accidents have been reported due to the fragility of the PTFE hose, the
risk of crushing, the porosity of PTFE to chlorine and the poor resistance of stainless
steel in a moist chlorine atmosphere.

See GEST 78/73 - Design principles for installations for off-loading of liquid
chorine road and rail tankers and tank containers.

October 1999 Page 4 of 34

 GEST / AP 2

GEST 75/43 - Flexible steel coils for the transfer of gaseous or liquid chlorine
GEST 75/44 - Articulated arms for the transfer of gaseous or liquid chlorine
GEST 75/45 - Flexible Monel and Hastelloy hoses for the transfer of gaseous or
liquid chlorine

 Use of pneumatic valves

Valves recommended by Euro Chlor have been installed for many years on barrels for
the transport of bulk liquid chlorine, to allow for automatic or remote operation. There
is no justification for not using such valves.

See GEST 78/73 (as above) for the recommended procedure for liquid chlorine off-
loading.

 Safety absorption unit

According to GEST 94/215 – Confinement of Units Containing Liquid Chlorine, if a

containment building is used, there should be a safety absorption unit designed and
able to be operated instantaneously and efficiently in case of a chlorine leak. This was
not the case in this incident, since only water sprinklers were available and it took time
to bring them into operation.

Conclusion

The cause was an accumulation of design and operational human errors, as described
above.

Additionally, the investigation showed that:

 The staff had insufficient knowledge of the risks associated with chlorine handling
and insufficient training.

 The emergency plan was too slow to operate.

 External communication was very poor.

It should not be forgotten that the chlorine supplier has a responsibility to assist the
facility operator in carrying out a safety audit of the plant to ensure it is fit for purpose.

October 1999 Page 5 of 34

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II. BACK-FLOW OF CHLORINE INTO INSTRUMENT AIR NETWORK

Process Description

Chlorine is compressed with a reciprocating compressor from 3.6 to 7.6 barg (see
figure 1). Prior to maintenance, chlorine can be purged to an absorption unit using a
permanently connected dry air supply at the inlet of the compressor. The air supply
can be isolated with manual valves. The pressure of the air (5.5 barg), which is taken
from the instrument air system, is higher than the normal pressure of the chlorine at
the inlet of the compressor (3.6 barg).

Circumstances of the Incident

The compressor had just been reinstalled after maintenance. A few minutes after the
start-up of the compressor, first with air and then with chlorine, it was decided to stop it
because of pressure perturbations on the chlorine process side.

The compressor was decompressed to the chlorine absorption unit, then was started
again, with valves 1 and 3 closed and valves 2 and 4 opened, in order to purge
remaining chlorine (see figure 1). The pressure at the inlet of the compressor was at
this time higher than the air pressure, so chlorine went back into the air network.

A small chlorine leak occurred in the control room through pneumatic instrumentation.
Operators carried out an emergency shut-down of the cell-room. There were no
injuries, but some damage was done to instrumentation.

Findings of the Investigation

While reinstalling the compressor after maintenance, an error was made: the two
cylinder valves on one of the three heads of the compressor were mounted in the
wrong direction.

After start-up, a back-flow of chlorine occurred inside the compressor due to the direct
connection between the high and low pressure sides. The chlorine pressure at the inlet
was then higher than usual: 7.6 instead of 3.6 barg.

Learning from Incident

The incident was mainly due to three factors:

 Error during maintenance: valves on one of the heads were mounted in the wrong
direction,
 Existence of a permanent connection between instrument air and chlorine,

October 1999 Page 6 of 34

 GEST / AP 2

 No means of checking process pressure before connection to the air network (no
pressure indicator at the inlet of the compressor when valve No 1 is closed).

Recommendations

 Permanent connections between air and chlorine should not exist, even if normal
pressure of chlorine is lower than normal pressure of air, and the valves are
opened only for maintenance operation.
 Instrument air should never be used for any operation on the process: it is
necessary to have a separate and dedicated network of dry process air, or
nitrogen.
 During safety studies, special attention has to be paid to back-flow of process fluids
into utility networks, either as a result of process pressure increasing or utility
pressure decreasing. Particular operations, such as start-up after maintenance,
must be studied very carefully.

Effluent treatment

No 4

No 1

Chlorine 3.6 barg Chlorine 7.6 barg

No 2 No 3

Compressor 3 heads

Air 5.5 barg

Cylinder valve
Isolation valve

Figure 1

See GEST 92/169 – Guidelines for the Safe Handling and Use of Chlorine
and GEST 87/133 – Over Pressure Relief of Liquid Chlorine Installations

October 1999 Page 7 of 34

 GEST / AP 2

III. LIQUID CHLORINE LEAK AFTER PUMP START-UP

Process Description

A liquid chlorine pump was used to fill rail tanks from general storage.

A simplified flow diagram is attached (see figure 2).

Circumstances of the Accident

During the start-up operation (cooling of the pump by flushing with liquid chlorine), one
degassing valve on the discharge line was left open. Liquid chlorine filled the liquid
trap (the low temperature alarm was wrongly interpreted), then reached the gaseous
effluent system.

Liquid chlorine was then discharged to atmosphere through a hydraulic seal located at
the purge of the effluent fan section.

One person working nearby was injured and was detained in hospital for 3 days for
observations. Five people outside the site were slightly affected and suffered from eye
irritation. The chlorine leak was estimated between 100 and 200 kg.

Learning from the Accident – Conclusion

The analysis of the accident led to the following actions:

Training of the operators on the start-up procedures of the liquid chorine pump, in
order to focus on the temperature alarm interpretation. This alarm was frequently
activated, due to an incorrect application of the procedure during the cooling of the
pump.

NB: the start-up procedure includes a cooling step of the pump. This is to avoid
vaporisation of liquid chlorine which would prevent the pump priming.

Improvement of the isolation procedure and its application, in order to clarify the
start-up step, including a check-list. Note that the degassing valve is rarely used.

Technical modifications

The accident revealed that instrumentation of the liquid trap is essential. Secondly,
that a wrongly positioned valve on the vent circuit could lead to a rapid chlorine
emission. As the consequences the following modifications were carried out:

October 1999 Page 8 of 34

 GEST / AP 2

 HLS (High Level Safety) on the chlorine trap, in addition to the existing LTA (Low
Temperature Alarm),
 Second trap after the existing instrumented trap to increase the retention capacity.
 A second storage section with its own liquid trap was equipped with the same
safety devices.

Recommendations

 See GEST 83/119 – Canned Pump for Use with Liquid Chlorine
 See GEST 81/106 – Chlorine Absorption System

CHLORINE PUMP USED FOR RAILTANKS

FLOW DIAGRAM (simplified)

R R R LIQUID CHLORINE STORAGES

Legend
Opened valve

Closed valve

EFFLUENT FANS

LIQUID
CHLORINE
LIQUID CHLORINE
PUMP
EMISSION
HYDRAULIC SEAL
LIQUID CHLORINE TRAP

FIGURE 2

October 1999 Page 9 of 34

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IV. NCl3 EXPLOSION AS A RESULT OF BRINE CONTAMINATION

WITH UREA

Process Description

A chlorine manufacturing process contains a 2 stage chlorine compressor with liquid

chlorine pre-cooling and inter-cooling. There is regular blow down of the liquid chlorine
to ensure that enrichment of nitrogen trichloride is kept under control. The blowdown
liquor is fed to a chlorination process and replenished with fresh liquid chlorine from
storage.

Frequent analysis for NCl3 is carried out and typical levels prior to blowdown are
2,000 ppm w/w.

Incident

Following a blowdown operation, a copper flexible exploded as it was being degassed

prior to disconnection from the blowdown drum. There was a minor injury.

A liquid sample was taken from the pre-cooler for laboratory NCl3 analysis before
taking any further action. During analysis, a further small explosion occurred in the
laboratory fume cupboard.

Findings of the Investigation

Cell-room feed brine was routinely analysed for nitrogen/ammonia species but the test
was insufficiently reliable to detect urea contamination in soda ash supplies used for
brine treatment. It is estimated that NCl3 levels in the precooler had arisen to 20,000
ppm w/w. Evaporation of the liquid chlorine in both the hose and laboratory sample
had enriched the NCl3 concentration to explosive levels.

The analysis of NCl3 in liquid chlorine requires the addition of a reagent to render it
safe. Insufficient reagent was added because NCl3 levels were never expected to be
so high.

Learning from the Incident

Wherever there is the potential for NCl3 enrichment, quality control checks and
analysis routines need to be rigorously applied.

October 1999 Page 10 of 34

 GEST / AP 2

Conclusion

NCl3 levels were unusually high because of urea contamination of cell-room feed
brine. Controls on preventing a potential contamination were inadequate, as well as
the procedures for analysis of unusually high NCl3 levels.

Recommendations

The potential for unacceptably high NCl3 levels must initially be prevented by controls
on cell-room feed brine quality. This requires reliable quality control of raw material
supplies to the process and sufficiently regular brine analysis for nitrogen and
ammonia species.

See GEST 76/55 – Acceptable Levels of Nitrogen Trichloride in Liquid Chlorine.

Analysis for NCl3 must take account of possible very high levels by the correct use of
reagents and techniques with a full appreciation of the potential danger.

See Anal 2 –Determination of NCl3 in Liquid Chlorine.

October 1999 Page 11 of 34

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V. PLANT START-UP AFTER MAINTENANCE: CHLORINE

EMISSION DUE TO HUMAN ERRORS

Installation

A chlorine liquefaction unit is equipped with small tanks to provide a hydraulic seal
between the condenser and the storage tanks (see figure 3). These seals avoid the
risk of explosive hydrogen/chlorine mixtures entering the storage tanks from the
liquefaction unit.

For safety reasons and in order to obtain high reliability in maintaining a liquid level,
these seals are equipped with two level transmitters. One of them forms part of an
automatic level control loop to regulate the valve sending the liquid chorine into the
storage tank. Any discrepancy between the two signals gives an alarm to the
operators.

The exit gas line goes to the chlorine absorption unit, and normally passes through a
safety tank, where any entrained liquid is trapped. This tank is equipped with level and
temperature detectors to alarm the operators in the event of liquid chlorine carry-over.

Circumstances of the Accident

The chlorine production and liquefaction unit was shut-down for several days for
modification and repair. This included the replacement of one level transmitter on the
seal tank.

Due to a misunderstanding between the maintenance and the production staff, the
impulse valves of both level transmitters were left closed, after the transmitters were
checked and the equipment was dried. Each supervisor (maintenance and production)
believed the other was in charge of the final checking and the installation was started
up in those conditions.

Due to materials problem with the safety trap on the gas line, this tank was by-passed
during the start-up of the unit.

During the first phase of the operation, when no liquid chlorine exists in the liquefaction
unit, the level control valve sending the chlorine into the production tank is closed
manually. The operator opens it only when he sees an increase in the level transmitter
signal. The level control system is then transferred to automatic control.

Since the impulse valves were closed, the two level transmitters continued to indicate
zero level, even when liquid chlorine started to accumulate in the vessels. Finally,
liquid chlorine filled the small seal tank and the condenser, and entered the pipe
leading to the safety absorption unit.

October 1999 Page 12 of 34

 GEST / AP 2

Since the safety trap was by-passed, no alarm occurred. Chlorine escaped via a
hydraulic seal on this pipe and the plant was immediately shut-down.

Learning from the Accident

After analysis of the incident, the safety trap was immediately redesigned to prevent its
being by-passed, and ensure it remained in operation even during the start-up of the
plant. Clear procedures were written to define the operations to be performed and
the responsibility of each team during such maintenance work; a check-list of all the
equipment that has been modified during the shut-down is used for the final control,
and the production supervisor is in charge of verifying that the production installation is
completely operational before deciding to start-up.

Cl2 gas

LT

liquefaction

Cl2 trap

Cl2 gas

Cl2 liquid

LT

Production tank

FIGURE 3

Recommendations

See GEST 76/52 – Equipment for the treatment of gaseous effluents containing
chlorine

October 1999 Page 13 of 34

 GEST / AP 2

VI. CHLORINE EMISSION AT THE START-UP OF AN INSTALLED

SPARE GAS BLOWER

Process Description

In a chlorine gas treatment unit, two blowers were installed, one in operation and one
spare, in order to transfer the gas at a limited positive pressure from the drying towers
to the liquefaction unit.

The blowers were constructed from titanium and fitted with carbon/Teflon labyrinth ring
seals with a wet-air purge to the chlorine suction side.

The spare blower was isolated by closed inlet and outlet valves. The air purge was
stopped but the suction side of the labyrinth ring seal was still open.

Circumstances of the Incident

When the operating blower needed some maintenance, the spare blower was started.

During this start, the labyrinth seals became unusually hot and some chlorine escaped
from the seal to the working area. The blower was stopped and inspected in the
workshop.

Findings of the Investigation

The air purge nozzles and lantern ring turned out to be very dirty and the seal rings
were seriously worn. The source of the dirt was the dust in the ambient air. The dust
could accumulate in the seal rings because of the continuous air flow resulting from
the open connection to the suction side (sub-atmospheric pressure) of the blowers
(see figure 4).

Measures Taken

To prevent any in-flow of fluids, the idle blower will be sealed from the process
installation by blind flanges (see figure 5).

Learning from the Incident

The blower performance is normally very reliable due to the quality of preventive
maintenance together with the materials of construction appropriate for wet chlorine.
As a result, the spare blower is idle for a much longer period than used to be the case
so giving ample time for dirt to accumulate in the seal rings.

October 1999 Page 14 of 34

 GEST / AP 2

The lesson to be learned is that safety awareness is important for stand-by equipment
connected to the production unit.
Recommendation

A safety study of process units, on a regular basis, using techniques such as e.g.
HAZOP or Quantitative Risk Assessment studies could be a valuable tool to prevent
this type of incidents.

See also Euro Chlor recommendation GEST 87/130 – Hazard Analysis for Chlorine
Plants.

water
air

drain

pressure line

Suction line

BLOWER Operating BLOWER idle

FIGURE 4

water
air

drain

pressure line

Suction line

BLOWER Operating BLOWER idle

October 1999 Page 15 of 34

 GEST / AP 2

FIGURE 5

October 1999 Page 16 of 34

 GEST / AP 2

VII. LESSONS FROM AN ACCIDENT IN A NON-EUROPEAN WATER

PLANT

Process Description

A water plant purified the city's water with chlorine purchased in one-ton containers. At
the time of the emergency, two of these containers, linked by a manifold, were kept in
the plant's chlorination room. Each tank, containing liquid chlorine, was equipped with
two valves. Gaseous chlorine could be drawn through the top valve; liquid chlorine
from the bottom valve.

The operating procedure before the leak was to slightly open the bottom valve of both
containers simultaneously and then use a "heater" to help vaporise the liquid chlorine
before introducing it into water.

Circumstances of the Accident

A water treatment plant alarm indicated that chlorine was present in the atmosphere of
the chlorination room. An employee called his supervisor and then, without breathing
apparatus, entered the room to find and abate the leak. He was overcome by the gas
and exited.

Ten minutes later, when a second employee arrived, chlorine gas was seeping under
the doors and beginning to collect outside. The second employee also attempted to
enter the chlorination room without breathing apparatus and was forced outside, where
a plant supervisor found him and send him for medical treatment.

The supervisor called the local Fire Department. Meanwhile, the chlorine cloud
advanced southward from the treatment plant.

When fire fighters arrived, the plant supervisor told them that the leak could be
stopped by closing valves on the chlorine containers. Three properly protected
firefighters entered the chlorination room and concluded (wrongly it turned out) that
one of the steel containers was leaking, not a valve. Liquid chlorine was escaping in a
jet, settling to the floor and vaporising rapidly. The three person team did not have
equipment to cap the leak and left the room.

The leak continued unabated and the gas cloud spread rapidly. Since the plant is
located in a residential area, authorities began evacuating nearby residents. 1500 kg
chlorine escaped before the leak was capped.

Three and a half hours after the beginning of the accident, the leak was reported to the
nearest chemical emergency rescue team. The emergency team (not specifically a
chlorine team) arrived about 15 minutes later. By the time the team entered the room,
an ice formation around the leaking area (where the container valve connected to the
manifold) had curtailed the flow. The team was equipped with a chlorine emergency kit
designed to cap leaks in ton containers. When they removed ice and the manifold

October 1999 Page 17 of 34

 GEST / AP 2

connection, the flow of liquid chlorine resumed. The team applied a repair cap which
greatly reduced the leak but did not eliminate it.

Meanwhile, management of the chlorine distributorship learned of the incident through

news coverage. They immediately dispatched their own emergency team. These
experts arrived seven and a half-hours after the beginning of the incident. They sealed
the leak and completely abated the emergency eight minutes later.

Findings of the Investigation

The experts transported the container to their own premises where they inspected and
re-tested it. No defect was found. However, inspectors noted that the valve leading to
the site of the leak had been opened (apparently by the person who connected it to the
chlorination system) several turns past the recommended open position of one-and-a-
quarter turns.

Decisions taken included:

 Good training of the operators and regular emergency drills.

 Purchasing four new sets of self-contained breathing apparatus plus training of
plant workers so that they are able to don the equipment in 30 seconds.

Recommendation:

In case of an accident, immediately contact your chlorine supplier who will send the
nearest emergency rescue team to assist you.

Measures taken:

Instead of using chlorine in the liquid phase from two drums in parallel, take chlorine
only in the gas phase from one container. These measures cut the potential release
volume by a factor of nearly 1000.

Conclusion

The most striking lesson seems to be:

 Adapt your process to your needs

 Why vaporise liquid chlorine when the required flow rate can be obtained from a
single drum in the gas phase?

Another important lesson is that a minor incident – a valve difficult to close because it
was too widely open – can become a major problem when a correct evaluation of the
incident is not carried out and when personnel are not well trained, drilled and
equipped.

October 1999 Page 18 of 34

 GEST / AP 2

Recommendations

 GEST 88/138 – Small Chlorine Containers: Construction and Handling

 GEST 93/178 – Euro Chlor Emergency Assistance Scheme

October 1999 Page 19 of 34

 GEST / AP 2

VIII. LEAK ON A PUMP ASSOCIATED WITH A LIQUID CHLORINE

STORAGE

Process Description

A liquid chlorine canned pump is used to feed an organic chlorination reactor from a
chlorine process drum.

The flow is controlled by an automatic valve and the excess flow is recycled to the
storage.

To guarantee a pump minimum flow, there is another line from the pump discharge
fitted with an orifice plate to allow a permanent recycle flow to the process drum.

To avoid overpressure in the chlorine process drum, the drum is equipped with an
automatic pressure control system and a double relief valve system protected by
rupture disks.

A simplified flow diagram is attached (see figure 6).

CHLORINE
ABSORTION

PIC

Chlorine
storage

FO

Valve not existing

before the accident

PIC PIC
S

October 1999 Page 20 of 34

 GEST / AP 2

FIGURE 6

Circumstances of the Accident

Due to a low chlorine feed flow to the reactor, the plant was automatically shut down.
The automatic shut-down of the plant leads, amongst other things, to the shut-down of
the liquid chlorine pump.

Less than 2 minutes later, the suction line of the liquid chorine canned pump broke off
with sparks and yellow flames coming out of the pipe.

As it was impossible either to activate the manual valve on the storage or any valve in
the suction line, chlorine drained from the system.

The total amount of the chlorine in the storage was between 5 and 6,000 kg.
Approximately 2,200 kg of chorine was dispersed into the atmosphere. The rest,
cooled by its own evaporation, was neutralised with liquid sodium hydroxide.

The toxic cloud drifted towards an urban centre approximately 1,500 m distant from
the plant. Due to a very light wind (less than 2 m/s) and a high relative humidity, the
maximum local concentration detected was 25 ppm during 2 to 3 minutes.

Findings of the Investigation

The final cause of the accident was the auto-ignition of the pump internal components
but the initial cause is unknown (probably the instantaneous blockage of the rotor). As
the internals were completely destroyed, it has been impossible to carry out an
analysis.

Note: the pump was equipped with:

 Differential pressure indicator on the filters in the suction line, alarmed in control
room.
 Local pressure indicator on both suction and discharge lines.
 Temperature sensor with pre-alarm and high temperature trip.
 Flow sensor, with no-flow trip.
 Minimum flow with orifice plate.
 Over-intensity protection.
 Intensity rating indicator.
 Axial position indicator, alarmed in control room.
 Remote shut-down.
 Two chlorine environmental sensors, alarmed in control room.

Measures Taken

To prevent other accidents, the main measure taken has been to install a quick acting
valve at the outlet of the liquid chlorine process drum with remote operation from

October 1999 Page 21 of 34

 GEST / AP 2

several parts of the plant. This valve closes instantaneously if the pump is shut down
by one of the trip systems.

Other security system measures to prevent an accident:

 Modify plant trip systems to close instantaneously the automatic level control valve
in the chlorine feed to the process drum.
 Improve the protection of the pump.
 Connect the terminal axial positions of the pump to the automatic shut-down
system.
 Install a motor winding temperature sensor, with high temperature trip.

Recommendations

GEST 72/10 – Pressure Storage of Liquid Chlorine recommends liquid chlorine

storage is equipped with an automatic shut off valve.

GEST 83/119 – Canned Pumps for Use with Liquid Chlorine recommends high
integrity safety features including the winding temperature sensor.

Conclusion

Whilst some of the safety features recommended for chlorine pumps are optional, it is
essential that, if a chlorine process drum or if a storage tank has a bottom run-off, a
remotely-operable valve should be installed.

October 1999 Page 22 of 34

 GEST / AP 2

IX. LEAK IN A 500 KG DRUM IN AN AIRPORT FACILITY

Introduction

The accident reported shows lack of knowledge of basic facts about chlorine by the
management and workers of a water treatment plant in placing the drum under water.

Circumstances of the Accident

In the area of an airport, there was a waste water treatment unit which had been out of
service since 1985, but that still contained two 500 kg drums of chlorine.

These drums had been supplied before 1980 by a supplier of chemical products who
was no longer trading.

At the end of 1996, the municipal company treating the waste water sent a message to
a chlorine producer about the leak of chlorine from a drum.

A technical specialist visited the site of the incident. The drum involved had been
dumped in an old sewer full of water.

On removing the drum from the sewer, a honeycomb was observed and 5 of the
retaining screws had been corroded, possibly by the bees or the honey. There was a
minor leak of chlorine from this area of the drum.

A chlorine emergency team attended the site of the incident. The 5 screws were
changed and the drum was transported to a nearby factory.

Cause

 Lack of knowledge of safety procedures of liquid chlorine storage.

 No periodic inspection of the drums.

Recommendations

See:

 GEST 72/10 – Pressure Storage of Liquid Chlorine

 GEST 81/97 – Chlorine Handling and Safety: Pressure Storage of Liquid
Chlorine
 GEST 81/99 – Chlorine Handling and Safety: Nitrogen Trichloride
 GEST 88/138 – Small Chlorine Containers Construction
 GEST 91/169 – Guidelines for the Safe Handling and Use of Chlorine

October 1999 Page 23 of 34

 GEST / AP 2

Continuously Examine the accident records of the industry

Identify areas of apparent weakness

Determine remedial action

Produce good quality Promote high standards of

documentation on design knowledge, training
and operation of equipment and organisation

Help in safety auditing of users’ installations

October 1999 Page 24 of 34

 GEST AP / 2

FATALITIES DUE TO CHLORINE

45
40 39
40
35
30 EURO CHLOR
FIGURES

25
20
20 REST OF THE
15 WORLD
8
10
5 3 3

0
1969-1978 1979-1988 1989-1998
PERIOD

October 99 Page 25 of 34
 GEST AP / 2

Flow Chart illustrating the way Euro Chlor works within the concept of
“Responsible Care

NUMBER OF FATALITIES DUE TO CHLORINE

IN THE EURO CHLOR COUNTRIES

50
45
40
40
Number of fatalities

35
30
22
25
20
15
11 8
10 5
4 4 3
5
0
21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-98
Ten years period

October 99 Page 26 of 34
 GEST AP / 2

NUMBER OF FATALITIES
PER MILLION TONS CHLORINE PRODUCED
IN THE EURO CHLOR COUNTRIES

0.81
1.00
Number of fatalities / Mt Chlorine

0.80

0.60

0.40
0.10 0.10 0.03 0.04
0.20

0.00
51-60 61-70 71-80 81-90 91-98

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FATAL ACCIDENTS DUE TO CHLORINE INHALATION 1953 - 1998

IN EURO CHLOR MEMBER COUNTRIES

Number of Number of
Fatal accidents Fatalities
Summary
* Producers' site 8 11
* Packagers and Users' 8 8
site 1 4
* Transport
Grand Total 17 23

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FATAL ACCIDENTS DUE TO CHLORINE INHALATION 1953 - 1998

IN EURO CHLOR MEMBER COUNTRIES
(continued)

Number of Number of
Fatal Fatalities
accidents
Production, bulk transport and use
* Chlorine gas production and
maintenance 2 3
* Liquid chlorine production 1 1
* Hydrogen chlorine explosions 3 4
* Loading, unloading and safety
absorption 2 2
Storage 0 0
Bulk transport 0 0

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Total 8 10

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ACCIDENTS DUE TO CHLORINE INHALATION 1953 - 1998

IN EURO CHLOR MEMBER COUNTRIES
(continued)
Number of Number of
Fatal Fatalities
accidents
Drums and cylinders
Plug rupture during transport 1 4
Drum weld failure 1 2
Cylinders bursting 2 2**
Cylinder switch-over in swimming pools 1 1
Total 5 9
Acid-hypo mixing
 By a retailer 1 1
 In a swimming pool 1 1*
Total 2 2
Swimming pools and water treatment
Chlorination system 2 2

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Total (for swimming pools, 4 4

included above mentioned accidents)
* Not a worker ** Maybe 1 non worker

NUMBER OF FATALITIES DUE TO CHLORINE EXPOSURE

IN THE EURO CHLOR COUNTRIES 1953 - 1998

BY TYPE OF ACTIVITY AND EQUIPMENT

Static Mobile Drums Cylinders Production Vaporizers Transfer Pipes Valves Hoses Various Total
ACTIVITIES vessel vessel vessels equipment

Transport by rail 0
Transport by road 0
Transport by water 4 4
Transport by pipe 0
Production gaseous chlorine 2 1 3
Production liquid chlorine 4 1 5
Absorption destruction 0
Storage 0

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Loading - unloading 1 1 2
Packaging 0
User 1 3 1 2 7
Various 2 2

Total 5 0 6 3 3 0 0 1 2 0 3 23

CAUSES (IN PERCENTAGE) OF ALL ACCIDENTS DUE TO CHLORINE

(WITH OR WITHOUT RELEASES) BY TYPE OF ACTIVITY

IN THE EURO CHLOR COUNTRIES 1953 - 1998

Loss of mechanical integrity due

to
Overpressure Instrument Valves Incorrect or Reaction Human
ACTIVITIES
or or incorrectly wrongly NaOCl error Unknown Total
External Corrosion Chemical
overheating electrical set or fitted + acid
forces erosion reaction
failure passing gaskets
Transport by rail 5.0% 0.4% 0.2% 0.8% 0.6% 2.3% 0.9% 10.3%
Transport by road 1.9% 0.3% 0.1% 0.2% 0.2% 0.1% 1.7% 0.5% 4.8%
Transport by water 0.3% 0.2% 0.1% 0.1% 0.1% 0.1% 0.1% 0.9%
Transport by pipe 0.2% 0.2% 0.2% 0.1% 0.1% 0.1% 0.4% 1.2%
Production chlorine 0.8% 1.1% 3.2% 1.2% 1.6% 0.8% 0.1% 2.4% 2.1% 13.5%

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gas
Production liquid 0.4% 2.9% 1.9% 0.7% 0.5% 1.0% 0.7% 2.2% 1.0% 11.4%
chlorine
Absorption destruction 0.1% 0.2% 0.1% 0.4% 1.4% 0.6% 0.6% 1.8% 0.7% 5.8%
Storage 0.3% 0.6% 0.6% 0.5% 0.2% 0.5% 0.4% 1.1% 0.8% 4.9%
Loading - unloading 1.0% 1.3% 0.5% 0.5% 0.3% 2.0% 1.2% 0.6% 4.7% 0.7% 12.8%
Packaging 0.2% 0.3% 0.3% 0.1% 0.2% 0.1% 0.3% 0.6% 0.6% 2.5%
User 0.9% 2.4% 1.6% 0.6% 0.7% 1.8% 0.6% 3.6% 7.1% 7.2% 26.7%
Various 0.1% 0.5% 0.1% 0.1% 0.2% 1.4% 1.4% 1.4% 5.1%

Total 11.1% 10.3% 8.7% 4.1% 4.7% 8.1% 4.4% 6.6% 25.5% 16.5% 100.0%

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