EMERGENCY ISOLATION OF CHEMICAL PLANTS

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Process Safety Guide:
GBHE-PSG-001
EMERGENCY ISOLATION OF
CHEMICAL PLANTS
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Process Safety Guide: Emergency Isolation of
Chemical Plants
CONTENTS
1 Introduction
2 When should Emergency Isolation Valves be Installed
3 Emergency Isolation Valves and Associated Equipment
3.1 Installations on existing plant
3.2 Actuators
3.3 Power to close or power to open
3.4 The need for testing
3.5 Hand operated Emergency Valves
3.6 The need to stop pumps in an emergency
3.7 Location of Operating Buttons
3.8 Use of control valves for Isolation
4 Detection of Leaks and Fires
5 Precautions during Maintenance
6 Training Operators to use Emergency Isolation Valves
7 Emergency Isolation when no remotely operated valve is available
References
Glossary
Appendix I Some Fires or Serious Escapes of Flammable Gases or Liquids
that could have been controlled by Emergency Isolation Valves
Appendix II Some typical Installations

Emergency Isolation of Chemical Plants
1 Introduction
Many serious fires have occurred in the oil and chemical industries
because leaks of highly flammable gases or liquids could not be
contained. For example, the serious fire at Feyzin in France in 1966
started while water was being drained from a tank of liquefied petroleum
gas. The drain valves could not be shut, LPG flowed out and was ignited
by a car on a motorway 500 feet away. Many fires have occurred as a
result of gland leaks on pumps handling very cold liquefied hydrocarbons.
Appendix I describes some incidents that could have been prevented
by the installation of emergency isolation valves. They were all the result
of leaks of flammable gases or liquids. On other plants equipment failure
or human failure has led to leaks of toxic gases or vapors or corrosive
liquids, but these do not seem to be so well documented.
As a result there is a need to provide means of isolating leaks before they
fire or before serious damage or injury results. This guide is intended to
help plant designers and operators decide when emergency isolation
valves should be provided and it gives some details of types that have
been used. It is suggested that new and existing plants handling toxic or
flammable materials should be reviewed in the light of this guide.
2 When should Emergency Isolation Valves be Installed?
It is impracticable to install emergency isolation valves to isolate every
piece of equipment which might leak. They should be installed only when
the chance of a leak is significant or the consequences serious. The
former usually occurs on equipment subject to extremes of temperature or
pressure, particularly if it is also subject to thermal shock, or subject to
vibration. In practice, the weakest points are usually pump glands,
followed by stirrer glands and reciprocating compressor glands In addition,
experience shows that water drain points are often left running
unattended.

Prevention of the leak in the first place is, of course, far better than
isolating it after it has occurred. It would be better to spend $2,000 on
making sure a pump does not leak than on providing a valve to isolate the
pump when it starts to leak. However, in many cases it is not possible to
reduce the chance of a leak to an acceptable level and emergency
isolation valves should then be installed.
When deciding whether or not to Install emergency isolation valves, the
size and consequences of a leak must be considered as well as the
probability that it will occur. Three situations should be considered:-
(a) The equipment is particularly liable to leak for example, very hot or
cold pumps.
(b) The equipment is less likely to leak but if it does leak a very large
quantity of material will run out and there is no way of stopping it,
for example, the bottom pump on a still containing more than, say,
50 tons, of flammable Liquid.
(C) The equipment is less likely to leak but if It does so, the rate of
leakage will be very large For example, a very large pump.
In addition, if the inventory between the emergency isolation valve and the leak is
large, or if the isolation valve is unlikely to give a good shut off, then an
emergency blow-down valve may be needed as well as an emergency isolation
valve.
The following illustrates the kind of argument that may be used to decide whether
or not emergency isolation is justified in a particular case:-
Suppose the cost of installing an emergency isolation valve (or motorizing an
existing valve) is $1,650.
Suppose a leak on the equipment being protected could lead to damage and loss
of profit worth $1,650,000.
Then if the chance of a leak of this size is greater than 1 in 1,000 in the life of the
plant (or in 10,000 per year) the expenditure is justified as an insurance policy,
quite apart from any risk to life.

Accurate data on the frequency of gland failure is usually not available. However,
it is not always necessary. Our experience may tell us that the chance of a fire is
a lot less than 1 in 1,000, or our experience may tell us that the chance of a fire is
a lot greater than 1 in 1,000. In either of these cases the problem is solved as we
know what action to take; it is not worthwhile looking for data on the frequency
of pump fires or trying to synthesize a figure from the reliability figures for seal
components.
If, however, our experience tells us that the chance of a fire is about 1 in 1,000
(say, between 1 in 100 and 1 in 10,0001 in the lifetime of the plant then it is
worthwhile expending some effort in trying to obtain more accurate data on the
frequency of pump fires.
If experienced judgment has to be used to estimate the probability of a leak,
why not use experienced judgment to decide whether or not an emergency valve
is necessary? The answer is that it is easier to estimate a piece of missing data
than to estimate the answer to a whole problem.
In some cases, particularly where toxic or corrosive materials are concerned, the
chance of damage to equipment is small but there is a significant risk of injury to
people. The methods of hazard analysis can be used in these cases. It is
necessary to estimate:
(a) The chance that a leak will occur.
(b) The chance that a man will be near enough to be injured at the time - this
can be estimated by measuring the 'population density' in the area. For
corrosive liquids, we also need to know the chance that the man will be In
the line of fire, i.e. what is the solid angle of the leak.
From these figures the probability that a man will be injured can be estimated
and compared with the usual criteria (Refs. 1,2 and 3).
Similar arguments can be used to decide whether or not emergency isolation
valves should be fitted on process drain lines. The chance of an uncontrolled
leak should be considered as well as the total quantity that can run out. As
already stated, experience shows that operators are reluctant to spend long
periods of time waiting whilst draining water from oil tanks. Despite instruction to
the contrary, they leave the drain point unattended. If they forget to return in time,
or the quantity of water is less than expected, a leak occurs. As a general rule,
remotely operated isolation valves should be installed on all process drain lines
on storage tanks or process vessels containing LPG. Drain points used only for
maintenance should be blanked off. (Ref 4).

Occasionally a plant contains a number of possible points of leakage and
fitting remotely operated isolation valves to all of them may be
impracticable. In these cases it may be possible to minimize the extent of
the leak and the consequences of any subsequent fire by dividing the
plant into sections by a number of emergency isolation valves.
Another method is to group points of leakage so that they are protected by
a single valve. For example, on LPG storage vessels, there should be only
one outlet below the liquid 'level, protected by a remotely operated
isolation valve, and all pump suction lines, drain points, sample points,
instrument connections etc. should come after this valve (Ref. 4).
Finally; the need to isolate the feed to a plant in an emergency must not
be overlooked. An emergency valve on the feed line may be desirable.
Hoses or flexible arms used for loading liquefied flammable gases or
liquefied toxic gases such as chlorine or ammonia into road or rail tank
wagons or ships' tanks have broken on many occasions. Filling lines
should, therefore, be fitted with remote isolation valves and the tankers
fitted with a non-return valves (or remote isolation valves if the same line
is used for filling and emptying).
Remotely operated isolation valves are better than excess flow valves as
the latter operate only when the leak rate is 50% or more above the
normal flow; heavy leaks can occur without them operating.
When pipelines are large, power operated emergency valves installed
primarily for safety reasons have been used instead of ordinary isolation
valves In order to avoid the effort involved in operating large hand valves.

3 Emergency Isolation Valves and Associated Equipment
3.1 Installations on Existing Plant.
When emergency isolation valves are being installed on an existing plant,
it is usually cheaper and more convenient to motorize an existing valve,
than to install a new one, as this would involve cutting lines. For example
to install a new valve at the point indicated below would be expensive and
involve a shut down. It would be cheaper and more convenient to fit
electric or pneumatic actuators on the two existing suction valves. This
has the additional advantage that the quantity of material that can leak
out, after the valves have been closed is much reduced. For liquids below
their boiling points at atmospheric pressure, the difference is not great, but
for flashing liquids the difference is considerable.
It is not usually considered necessary to fit emergency isolation valves on
pump delivery lines, as non return valves are normally fitted and prevent
back flow.
3.2 Actuators
Emergency isolation valves may be operated either electrically or
pneumatically (or hydraulically if a hydraulic oil supply is available on the
plant). For new installations fire-safe pneumatically operated ball valves
are preferred, for example, Wilmot-Breedon valves flitted With Truflo
actuators.

The following types of actuator have been used: -
Electrically operated
Rotork, Limitorque (with pneumatic operation if power fails) Jones· Tate
Pneumatically operated
Taylair (for gate valves)
Truflo (for ball vialves)
Hatlersley Newman (for ball or gate valves)
Typically, electrically operated valves take about one minute to operate,
pneumatically operated ball valves rather less and pneumatically operated
gate valves rather longer. No doubt other types are available and their
absence from this list does not mean that they are unsatisfactory.
3.3 Power to Close or Power to Open?
In most cases emergency isolation valves are held open by air pressure or
electric power and they will close when the pressure falls or the current is
isolated. If operators forget to operate these valves, and a fire occurs, then
the impulse lines will be burnt through and the valves will close. (A fusible
section in a mechanical linkage behaves similarly)
There are however exceptions:-
Power is needed to open and to close emergency isolation valves when
the valves are very large and, in some cases, when existing valves have
been motorized. Sometimes the valves are deliberately designed so that
air pressure or electric power is required to close them. This is done when
the consequences of a serious trip are serious, accidental closure of the
valves being less likely when power is required to close them.
In these exceptional cases, if we are dealing with flammable materials,
then the air lines or cables to the valves must be provided with 15 minute
fire protection.

3.4 The Need for Testing?
Emergency Isolation valves must be tested regularly, typically
once/month, or they may not operate when required. Often a valve can be
quickly closed and then opened without upsetting the process. If this is not
the case, a stop should be used to prevent the valve closing fully. The
stop must be removed after testing is complete. A complete test should be
carried out when the plant is shut down. An advantage of motorizing
existing pump suction valves, as shown on the diagram in Section 3.1, is
that testing presents no problems: each valve is tested while the other is
on line.
Non-return valves used in conjunction with emergency isolation valves, as
described above, must also be inspected (or tested) regularly. (Though as
simple mechanical equipment they will need inspections or testing less
often than pneumatic or electrical equipment).
3.5 Hand-operated Emergency Valves
If the suction vessel is some distance from the likely point of leakage then
a hand-operated emergency valve may be acceptable. It must be possible
to reach it when a leak occurs, without exposing the operators to undue
risk. A man should not be expected to go upstairs to operate an
emergency valve. These hand-operated emergency valves must also be
exercised regularly or they will be too stiff to operate when required In
anger. Note that moving the emergency valve further away from the point
of leakage increases the quantity of material that will continue to leak out
after the valve is closed and may strengthen the case for a blow down
valve, this is particularly Important if the liquid is above its atmospheric
pressure boiling point so that a lot of it has to flash to reduce the pressure.
In a few cases mechanical linkages have been used instead of electric or
pneumatic means to operate valves from a distance.
Sometimes, particularly on older plants, hand-operated valves are used
for emergency isolations but the operators are protected from the point of
leakage by walls. These are not recommended as the walls interfere with
ventilation and prevent the dispersal of small leaks.

3.6 The Need to Stop Pumps In an Emergency
When all emergency isolation valve is fitted on the suction of a
pump or a compressor, the motor should be tripped automatically when
the valve is operated otherwise the machine may overheat and set fire to
the leak.
3.7 Location of Operating Buttons
Care should be taken that the operating buttons for emergency isolation
valves are not so close to the likely point of leakage that they cannot be
reached when a leak or fire occurs. One serious fire occurred because this
point had been overlooked. Motorized suction valves had been installed
on a pump, primarily for process convenience, and the operating buttons
placed close to the pump. The fact that the valves might be required in an
emergency had been overlooked (Ref 5).
Of course, the operating buttons should not be too far away or there will
be delay before they can be operated. On many installations there is one
button about 30 feet away and another in the control room.
3.8 Use of Control Valves for Isolation
Control valves are sometimes used as emergency isolation valves. They
do not give as good an isolation as a valve designed for the purpose but
when a control valve exists, installation of an additional valve may not be
justified. On other occasions a control valve is used to back up a special
emergency valve.
If a control valve is to be used as an emergency valve a special
emergency button should be provided It should not be left to the operator
to close the valve by altering the control setting.

Flowchart for selection of ALARP Isolation Methods

Examples of methods for securing isolations
4 Detection of Leaks and Fires
Emergency isolation valves are of little value if we do not know when a
leak or fire occurs so that the emergency valves can be actuated. Unless
operators are present on the plant most of the time, it is usually necessary
to install leak or fire detectors in conjunction with remote isolation valves.
For flammable gases or liquids, combustible gas detectors are usually
preferred to fire detectors as they detect leaks before they fire. Sieger
flammable gas detectors are of proved reliability. For advice on fire
detectors see Ref.6.

5 Precautions during Maintenance
Several accidents have occurred (Ref 12) because motorized valves were
used to isolate equipment which was under maintenance and power was
accidentally isolated or restored.
If power opens the valve, then the power must he disconnected before
equipment is given to maintenance, i.e., on electrically operated valves the
fuses must he withdrawn, on pneumatically or hydraulically operated
valves the impulse lines must be vented and the vent valves locked open.
If power keeps the valve closed then it must be held shut by a locked
clamp strong enough to withstand the loss of power Simple clamps which
give a little when power is removed, thus allowing the valve to open
slightly, are not suitable
6 Training Operators to use Emergency Isolation Valves
Operating emergency isolation valves usually results in the interruption of
process flow and the shut-down of the plant. Operators are therefore often
reluctant to use them. Not only do they wish to maintain production but the
subsequent start-up of the plant may involve them in extra work. On a
number of occasions experienced supervisors have entered the vapor
cloud around a leak of flammable gas or liquid In order to shut down a
leaking pump and start up the spare instead of using the emergency valve
provided
The need to avoid taking unnecessary risk should be emphasized during
operator training In the diagram in Section 3.1, motorizing the two suction
valves near the pumps, instead of installing a single notarized valve next
to the suction vessel, will overcome the reluctance of operators to interrupt
the process.

7 Emergency Isolation when No Remotely Operated Valve is Available
However many remotely operated isolation valves are installed, it is
always possible that a leak will occur on equipment which is not fitted with
one. The men on the job then have to decide whether they should take a
chance and enter a vapor cloud to close a valve or whether they should
allow the leak to continue. In these cases it is often possible to push back
the vapor with water sprays and approach the valve behind the water. This
technique can be used leaks that are on fire and with leaks that have not
fired.

References
1 'Hazard Analysis - A Quantitative Approach to Safety' I Chem E
Symposium Series No. 34, 'Major Loss Prevention in the Process
Industries', p. 75.
2 'Specifying and Designing Protective Systems', Loss Prevention, Volume
6,1972, p 15.
3 F ire Detection Newsletters, obtainable from Central Safety Department.
4 'Case Study of a Reactor Fire', RM Zielinski, Chm. Eng. Progr., August,
1967, 63, No.8, P. 50.
5 Verbal report by EW Langley of HM Factory Inspectorate, Chemical
Branch, 1966, Chemical Age, 8 March 1970.
6 NFPA Quarterly, July 1951 (Reprint No. Q45-3)
7 NFPA quarterly, October 1961 (Reprint No. 055-5)
8 Report No. 0.21, 100/B, 'Report on a Fire on No.2 Crude Oil Distillation
Plant', TA Kletz, 7.7.69.
9 Safety Newsletters No. 42, Item 2 and No. 57, Item 5.
10 Report No. 0.21,186/B, 'Safety in Design of Plants Handling Liquefied
Light Hydrocarbon - Review of Work Camed out Mid-1966 to Mid-1970',
Appendix 1. by HG Simpson, 22.12.70.
11 Management of health and safety at work. Management of Health and
Safety at Work Regulations 1999. Approved Code of Practice and
guidance L21 (Second edition) HSE Books 2000 ISBN 0 7176 2488 9
12 The tolerability of risk from nuclear power stations HSE Books 1992 ISBN
0 11 886368 1
13 Successful health and safety management HSG65 (Second edition) HSE
Books 1997 ISBN 0 7176 1276 7

14 Internal control: guidance for directors on the combined code and
Implementing Turnbull: a boardroom briefing, both published by the
Institute of Chartered Accountants in England and Wales in 1999, are
available at www.icaew.co.uk
15 Safety signs and signals. The Health and Safety (Safety Signs and
Signals) Regulations 1996. Guidance on Regulations L64 HSE Books
1996 ISBN 0 7176 0870 0
16 Safe use of work equipment. Provision and Use of Work Equipment
Regulations 1998. Approved Code of Practice and guidance L22 (Second
edition) HSE Books 1998 ISBN 0 7176 1626 6
17 Guidelines for the Management, Design, Installation and Maintenance of
Small Bore Tubing Systems EHS16 Institute of Petroleum 2000 ISBN 0
85293 275 8
18 BS EN 764-7: 2002 Pressure equipment. Safety systems for unfired
pressure vessels British Standards Institution ISBN 0 580 39863 3
19 Reducing error and influencing behavior HSG48 (Second edition) HSE
Books 1999 ISBN 0 7176 2452 8
20 Guidance on permit-to-work systems: A guide for the petroleum, chemical
and allied industries HSG250 HSE Books 2005 ISBN 0 7176 2943 0
21 Manual handling. Manual Handling Operations Regulations 1992 (as
amended). Guidance on Regulations L23 (Third edition) HSE Books 2004
ISBN 0 7176 2823 X
22 Control of substances hazardous to health (Fifth edition). The Control of
Substances Hazardous to Health Regulations 2002 (as amended).
Approved Code of Practice and guidance L5 (Fifth edition) HSE Books
2005 ISBN 0 7176 2981 3
23 Safe work in confined spaces. Confined Spaces Regulations 1997.
Approved Code of Practice, Regulations and guidance L101 HSE Books
1997 ISBN 0 7176 1405 0
24 Safe maintenance, repair and cleaning procedures. Dangerous
Substances and Explosive Atmospheres Regulations 2002. Approved
Code of Practice and guidance L137 HSE Books 2003 ISBN 0 7176 2202
9

25 Remotely operated shutoff valves (ROSOVs) for emergency isolation of
hazardous substances: Guidance on good practice HSG244 HSE Books
2004 ISBN 0 7176 2803 5
26 Guidelines for the Management of Integrity of Bolted Pipe Joints EHS15
UKOOA 2002
27 Memorandum of guidance on the Electricity at Work Regulations 1989
HSR25 HSE Books 1989 ISBN 0 11 883963 2
28 Electricity at work: Safe working practices HSG85 (Second edition) HSE
Books 2003 ISBN 0 7176 2164 2
29 BS EN 60947: 1998 Specification for low-voltage switchgear and
control gear British Standards Institution ISBN 0 580 29155 3
30 Work with ionizing radiation. Ionizing Radiations Regulations 1999.
Approved Code of Practice and guidance L121 HSE Books 2000 ISBN 0
7176 1746 7
31 Electrostatics. Code of practice for the avoidance of hazards due to static
electricity PD CLC/TR 50404: 2003 ISBN 0 580 42225 9
32 Petroleum and natural gas industries – pipeline transportation systems –
pipeline valves ISO 14313: 1999 International Organization for
Standardization
33 Institute of Gas Engineers IGE/TD/3 Edition 4 (1677) Steel and PPE
pipelines for gas Distribution 2003
34 BS 6990: 1989 Code of practice for welding on steel pipes containing
process fluids or their residuals British Standards Institution ISBN 0 580
16672 4
35 Institute of Gas Engineers IGE/TD/1 Edition 4 (1670) Steel pipelines for
high pressure gas transmission 2001
36 Approved Supply List. Information approved for the classification and
labeling of substances and preparations dangerous for supply. Chemicals
(Hazard Information and Packaging for Supply) Regulations 2005.
Approved List L42 (Eighth edition) HSE Books 2002 ISBN 0 7176 6138 5

37 Pipelines Safety Regulations 1996 SI 1996/825 The Stationery Office
1996 ISBN 0 11 054374 4
38 Institute of Gas Engineers IGE/SR/22 (1625) Purging operations for fuel
gases in transmission, distribution and storage 1999
39 BS 6739: 1986 Code of practice for instrumentation in process control
systems: installation, design and practice British Standards Institution
ISBN 0 580 15295 2
Glossary
baseline isolation standard the minimum acceptable standard of final
isolation applied under normal circumstances. This standard is based on
risk assessment. It can be determined using the methodology in Appendix
6 or by other means.
blank flange (blind) a component for closing an open end of pipe work,
which is suitably rated to maintain the pressure rating of the pipe and of an
appropriate material to withstand the contents of the line.
bleed or vent valve a valve for draining liquids or venting gas from a
pressurized system.
block valve a valve which provides a tight shut-off for isolation purposes.
double block and bleed (DBB) an isolation method consisting of an
arrangement of two block valves with a bleed valve located in between.
double-seated valve a valve which has two separate pressure seals
within a single valve body. It is designed to hold pressure from either
direction (as opposed to a single seated valve). It may include a body vent
between seals to provide a block and bleed facility.
extended isolation: isolation which is to remain in place for more than
three months.
fluid freely moving substance. Includes liquids and gases.

hazardous substance a substance which is able to cause harm or
damage if loss of containment occurs. In some cases (e.g. water) the
specific situation determines whether the substance belongs within this
category.
intolerable risk: risk at an unacceptably high level. Until the risk has been
reduced, activity should not be started (or continued). If the risk cannot be
reduced, even with unlimited resources, the proposed activity should not
go ahead.
isolating authority person authorized to approve proposed isolations.
isolation the separation of plant and equipment from every source of
energy (pressure, electrical and mechanical) in such a way that the
separation is secure. isolation envelope that part of the pipe work system
which is within the isolation points forming the boundary within which
intrusive work can be performed. Where a valved isolation allows a
physical isolation to be effected, it is the physical isolation point that forms
the boundary of the isolation envelope.
isolation envelope that part of the pipe work system which is within the
isolation points forming the boundary within which intrusive work can be
performed. Where a valved isolation allows a physical isolation to be
effected, it is the physical isolation point that forms the boundary of the
isolation envelope.
isolation scheme a system incorporating three key components –
management arrangements, risk control procedures and working-level
practices, to ensure hazardous substances are not released nor people
exposed to risks to their health and safety during the maintenance or
repair of process plant or pipelines.
own isolation: isolation where the same person both installs the isolation
and carries out the intrusive work. Such isolations may be carried out
under PTW or procedural control.
permit-to-work (PTW) a formal written system used to control certain
types of work which are hazardous.
pig a device that can be driven through a pipeline by means of fluid
pressure for purposes such as cleaning, dewatering, inspecting,
measuring, etc.

physical disconnection a method of positive isolation where an air gap
between the energy source and the plant/equipment is provided.
pipeline cross-country, offshore and pipelines within sites, for example,
storage sites, and petrochemical plant. This guidance uses the definition
of ‘pipeline’ given in BS EN 14161 i.e. ‘the facilities through which fluids
are conveyed, including pipe, pig traps, components and appurtenances,
up to, and including the isolation valves’. However, pipeline installations
such as compressor stations and pressure- regulating installations are not
included in this definition – these are considered separately. Note that this
differs from the legal definition of ‘pipeline’ within the Pipelines Safety
Regulations 1996 (PSR) which includes certain pipeline installations, e.g.
for gas pressure regulation. The relevant gas industry code for high
pressure steel transmission pipelines is IGE/TD/1 and for distribution
mains it is IGE/TD/3.
pipeline installation installations such as pressure regulating
installations, compressor stations which, together with the pipeline itself,
comprise a pipeline system (as defined in BS EN 14161). The relevant
gas industry code for pressure regulating installations is IGE/TD/13.
pipe work piping interconnecting items of process plant.
piping and instrumentation diagram (P&ID) schematic drawing defining
the extent of equipment, piping and piping components and
instrumentation.
positive isolation complete separation of the plant/ equipment to be
worked on from other parts of the system.
pressurized plant facilities containing liquid or gases under pressure for
treatment, processing or storage.
proved isolation valved isolation where effectiveness of the isolation can
be confirmed via vent/bleed points before breaking into system.
short-duration work: work which does not extend beyond one operating
shift.
slip-ring a spacer ring installed in pipe work to facilitate the insertion of a
spade.

spade (slip-plate) a solid plate for insertion in pipe work to secure an
isolation. The spade must be of an appropriate material to withstand the
line contents.
spared equipment: equipment which is available to replace on-line
equipment, e.g. during maintenance or in the event of breakdown.
spectacle plate a combined spade and slip-ring.
tagging temporary means of identifying a valve or other piece of plant.
variation a situation where circumstances require the use of an isolation
of a standard lower than the baseline isolation standard (or where
relevant, the established company standard). Use of a variation is
acceptable only when it is supported by a situation-specific risk
assessment. Variations must be appropriately authorized and fully
recorded.

APPENDIX I
Some Fires or serious escapes of Flammable Gases or Liquids that could
have been controlled by Emergency Isolation Valves
Except where stated, the following accidents are taken from reference 10.
1 Leakages from Pump Glands or Seals
Leakage from the seals of cold duty pumps on European Olefin Plants has
been a not uncommon occurrence. One of the leaks which fired was on
a Olefin Plant and it was a fortunate circumstance on this occasion that
other plant above the pump was screened from the fire by a solid concrete
floor. On another Olefin Plant there has been severe leakage from the
seals of the C2 splitter reflux pumps on a number of occasions, giving rise
to a cloud of vapor which, prior to the installations of the firewall and
steam curtain in 1968, created a hazard on a Works road on 35 ft away.
The vapor cloud from a major seal failure on one of the pumps in 1969
was contained and dispersed by means of the steam curtain.
Another Company reported three major leaks from seals of cold ethylene
pumps which occurred on different plants in 1968. The first resulted from
the failure due to stress corrosion of one of two bolts which held the seal
in position, allowing a large outflow of liquid which vaporized immediately
and generated a large volume of Vapor. The vapor cloud was fortunately
carried clear of adjacent flares and heaters by the wind blowing at the
time, and did not ignite. It was estimated that 90,000 ft3
of vapor (3 tons)
escaped in 20 minutes. The other two leaks both ignited near the pumps,
apparently due to discharge of static electricity, the escape occurring in
each case as a jet of vapor containing entrained droplets of liquid.
Pumps handling C3 and C4 hydrocarbons at ambient temperature and
moderate pressures have given little trouble with seal leaks on any
Petrochemical plant, but there have been a number of gland failures of
high pressure propylene injectors In 1956 there was an extensive fire,
which caused serious injury to personnel as well as damage to plant.
when gland studs failed and the cloud of vapor, escaping was ignited it the
furnaces of a plant some 200 ft away. Following this fire the Injectors were
resisted within a fire wall with steam ejectors, and were provided with
remote isolation valves.

A fire occurred In another European Petrochemical plant in 1972 when the
bearing and gland of a large hydrocarbon pump collapsed. The fire burnt
for 6 hours until it was found possible to drain the vessel feeding the fire,
but was successfully contained end did not spread to the rest of the plant.
The pump which leaked was provided With remotely operated isolation
valves, but as these were installed primarily for process use, the operating
buttons were placed near the pumps and could not be reached. By the
time a supervisor took a chance and dashed In to operate the buttons, the
electric cables to the actuators had been burnt through and the valves did
not operate (Ref. 5).
2 Leakage from Equipment Joints and Valves
The gasket of a level connection on the base of a reactor of a North
American Polypropylene Plant, ruptured suddenly in 1964, (Ref 71,
releasing "large cloud of propylene vapor. Immediate steps were taken to
reduce the pressure in the reactor by isolation of flows in, blow-down and
increased cooling of the Jacket, while a deluge system was activated
covering the area with a water spray to reduce the chance of electrostatic
ignition of the vapor and additional water, giving a total of 4000- 5000
gpm, was applied by fire hoses, to help disperse the vapor cloud. The
fire spread to neighboring units causing considerable material damage,
but fortunately only minor injuries to personnel.
3 Leakage from Equipment Fittings
Another company have reported a fire on the ethylene feed gas
compressor of a polyethylene plant which occurred when an escape of
gas from the vicinity of the discharge pressure gauge ignited. No one was
injured and the fire was extinguished after 40 minutes by shutting off the
feed to the compressor.

4 Spillages from Drain Valves
Two dangerous incidents have occurred on a European Petrochemicals
plant, both associated with blockage of drain valves by ice or hydrate
formation, In the first of these the drain valve on a butadiene storage
sphere stuck open after draining water, causing butadiene to spill in the
compound. The valve was closed after heating with a steam lance and the
spillage, which was not large, was dispersed with steam.
The compound wall was provided with a steam curtain which was
actuated, and tests with a combustible gas detector on the roadway
beyond the wall gave negative results In the second incident an amount of
butadiene estimated at several tons was found in the bund round a stock
tank. This had come from the drain of a torque tube, which had most
probably been blocked open by a piece of ice or hydrate which
subsequently melted.
The disaster at the Rhone Alpes refinery at Feyzin in January 1966 (Ref 8)
started with a blockage in the drain line from a propane storage sphere,
which was almost certainly due to ice or hydrate. The drain line had two
valves, and the open end pointed straight down to the ground below the
sphere. The standing Instruction on the draining operation was to open the
valve next to the tank fully, and control the draining with the second valve,
so leaving the opportunity to isolate the lank by the fist valve in the event
of any trouble with the second. On this occasion the operator, from
another refinery, controlled the draining on the first valve with the second
one wide open. When the first valve blocked he opened It wider, until the
obstruction gave way, and a jet of propane issued full bore through the 2
in line, striking the ground below and rebounding into the operators f, and
also so knocking the handle off the valve. Subsequent attempts to replace
the handle of the first valve, and to shut the second valve failed. The
resultant cloud of vapor was ignited at a point some 500 ft. away, and the
flame flashed back to the sphere and continued to burn under it until the
stock, originally 348 tons, was almost exhausted. Because of lack of
experience of the fire brigade combined with shortage of firewater, the
sphere was left without any cooling water in the belief that the relief valves
would prevent over pressuring. In the event the metal of the sphere failed
due to overheating, and the vessel ruptured, spreading the fire to
neighboring storage spheres. In all, 18 people were killed and 81 injured.

A fire on an ethylene plant at Varennes, Quebec, in April, 1968, was
caused in a similar way to the Feyzin disaster. A choke occurred during
draining, of an intermediate stage catchpot on the process gas
compressor, the operator opened both valves in the drain fully and the
choke cleared suddenly, releasing a cloud of hydrocarbon vapor. The
operator could not get to either of the valves to shut them and the cloud
ignited.
Another company has reported incidents on two different refineries in
which mal-operation of the water drain on a debutanizer reflux drum
allowed the escape of a large quantity of butane which was ignited some
distance way. In one incident the oil/water interface in the separator vessel
was lost, and an intermediate collecting pot provided was not used. The
butane escaping spread through the drainage system, and was ignited in
the vicinity of hot oil pumps. In the other incident the draining was done
through a closed system, relying on feeling the cooling of the pipe by
expansion of the butane when the interface was reached, and on this
occasion sufficient butane was released into the drainage system to
blow the water seals, giving a large escape of vapor over the ground
which again was ignited In the vicinity of hot oil pumps.
A fire occurred on a butadiene plant at Kobuta, Pennsylvania (Ref. 9)
when a 1/2 in. valve on a still bottoms pump was left open at the start up
of the pump, allowing the escape of a cloud of C4 hydrocarbon vapor
which was ignited at a frnace185 ft away. Two people were injured, and
the still was severely damaged.
5 Tank Wagon Hose Connections
Numerous failures of hose connections to liquefied hydrocarbon tank
wagons, followed by ignition of the escaping vapor have been reported by
the NFPA. Out of a total of 12 incidents, which occurred in the USA over
the period 1954- 1963, there were 5 hose bursts during loading or
offloading, 5 hoses were broken by driving the tank wagon off before
disconnecting, 1 hose was cut by being run over when the tank wagon
was moved slightly during offloading and 1 hose was burnt through by a
fire which started on a pump. People were killed in 4 of the Incidents, and
injured in 2 more. Sources of ignition where these were identified were
variously the tank wagon engine, an office heater, a boiler house,
a domestic cooker and a private car.

Excess flow valves prevented serious damage in one incident, but failed in
two other incidents, in one case because the rate of escape was too low
to operate them. In another incident the excess flow valves were found to
be wired open (Ref. 101.
6 Spillages when Opening up Plant for Maintenance Work
Emergency Isolation valves cannot as a rule, be Installed to isolate these
spillages as they are liable to occur almost anywhere on a plant. However,
they would have prevented a serious leak and fire which occurred in 1967.
A fitter opened up a pump for maintenance; hot oil carne out and caught
fire as the suction valve had not been isolated The oil was above its auto-
ignition temperature and caught fire. The fire resulted in the death of three
men and the destruction of the unit.
As the pump glands were liable to leak, the leaking oil was above its
autoignition temperature and the inventory was large, the case for an
emergency Isolation valve was good and one was fitted on the rebuilt
plant. (Ref. 11).

Characteristics of common valve types. The isolation circumstances should
always determine the valve selection

Appendix II - Some Typical Installations
1 LPG Storage
Figure (1), adapted from Ref 4, shows the arrangement recommended in
Ref. 4. There is only one connection to the vessel below the liquid level.
There is no flange, valve, instrument or drain under the shadow of the
vessel, but a remotely controlled fire-safe isolation valve is located on the
far side of a separation wall. All branches to pump suction lines, drain
lines, sample points, instruments, etc, come after this valve.
2 An Olefin Plant
The attached table lists all the likely sources of leakage on a European
Olefin Plant, the nature of the material, its temperature and pressure
and the inventory which will leak out if a leak occurs and it cannot be
isolated. It also shows whether or not an emergency isolation valve has
been fitted. The column headed 'A or B' refers to page 2 of the main
report. 'A' indicates that the equipment is particularly liable to leak, for
example very hot or cold pumps. In assigning this classification
experience in the industry as a whole is taken into account, and not just
experience on this plant. 'B' indicates that the equipment is less likely to
leak, but if it does leak, a very large quantity of material will run out,
and unless there is an emergency isolation valve, there will be no way of
stopping it.
Unless otherwise stated, emergency isolation valves are fitted only on the
suction lines of pumps and other items of equipment. Delivery lines are
normally protected by non-return valves.

Fig 1 General Arrangement of Piping to an LPG Storage Vessel

Remote Isolation Valves -European Olefin Plant

3 An Aromatics Plant
The attached table lists all the likely sources of leakage on a European
Aromatics Plant, the nature of the material, its temperature and
pressure and the inventory which will leak out if a leak occurs and it
cannot be isolated. A and B have the same meaning as in (2) above.
All the points where emergency isolation valves are fitted, have been
listed.
In addition, a number of points where they are not fitted, and there is no
intention to fit them, are noted for comparison.

Remote Isolation Valves - European Aromatics Plant

Isolation methods
1 Physical isolation of pressurized systems is primarily achieved using
various combinations of valves, spades and blank flanges.
2 Pipelines often have long sections of pipe between valves. You may need
to use techniques such as pipe plugs or pipe freezing to enable the
isolation of intermediate sections of pipe for maintenance purposes, when
it is not reasonably practicable to use primary devices (see Table
below). Such techniques are not appropriate for standard use on process
plant and should be subject to task-specific risk assessment and senior-
level authorization.
3 A summary of isolation techniques is given in Table below. This indicates
the key features and applications of each device.

Checklists for monitoring and review
Compliance monitoring checklist – do we do what we say we do?
The model list below should be tailored to suit your own isolation systems.
It should not be assumed to be a comprehensive model.
Forms should allow the checker to assign relative importance of non-
conformances, record the passing of the findings up the management chain to
agree/implement actions, etc.

Checklist for company review of adequacy of SMS for isolations
This checklist provides a basis (structured around the HSG653 model) for
reviewing the adequacy of your safety management system (SMS) for isolation
activities. Select the questions appropriate to your site and its hazards. You
should also assess whether any additional questions will be appropriate for your
operation.

EMERGENCY ISOLATION OF CHEMICAL PLANTS

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