A Guide to Safety and Health at Work for
Gas Welding and Flame Cutting
Occupational Safety and
Health Branch
Labour Department
Occupational Safety and Health Branch
Labour Department
4/99-1-B59
A Guide to Safety and Health at Work for
Gas Welding and Flame
Cutting
This guidebook is prepared by the
Occupational Safety and Health Branch
Labour Department
First Edition
April 1999
This guidebook is issued free of charge and can be obtained
from offices of the Occupational Safety and Health Branch.
Addresses and telephone numbers of the offices can be found
in the booklet“The Labour Department Offers You its Services”
or by telephone 2559 2297.
Contents
14. Useful Information
If you wish to enquire about this guidebook or require advice on
occupational safety and health, please contact the Occupational
Safety and Health Branch of the Labour Department through:
Telephone : 2559 2297 (auto-recording after office hours)
Fax
: 2915 1410
E-mail
: laboureq@labour.gcn.gov.hk
Page
1.
Introduction ............................................................
1
2.
Fire and Explosion Hazards ...................................
2
3.
Health Hazards ......................................................
3
4.
Gas Supply System and Associated Safety
Devices ..................................................................
5.
Information on the services offered by the Labour Department
and on major labour legislation can also be found by visiting our
Home Page in the Internet. Address of our Home Page is http://
www.info.gov.hk/labour.
4
Safe Storage and Handling of Gas
Cylinders ................................................................
6
6.
Fire Prevention and Protection ...............................
7
7.
Health Protection and Ventilation ...........................
8
8.
Personal Protective Equipment .............................
9
9.
General Safe Practices .......................................... 10
10. Equipment Checking and Maintenance ................ 12
11. Emergency Procedures ......................................... 14
12. Instruction and Training ......................................... 16
13. Unsafe Acts ............................................................ 17
14. Useful Information .................................................. 19
19
◆
1. Introduction
In gas welding and flame cutting, a fuel gas is mixed with oxygen
or air in a blowpipe to produce a flame hot enough to fuse the
surfaces together, or in case of cutting hot enough for the formation
of molten oxides of the metal involved. Fire and explosion are the
hazards that may be encountered due to problems with the gas
supply system or due to the hot slag resulted from the process.
Besides, toxic fumes and radiation produced during the process
may also pose health hazards to the people at work.
Warming up gas cylinders
Warming up gas cylinders by any means in order to increase
gas flow or to extract the last bit of gas stored in the cylinder
for use is extremely dangerous. Fire and explosion may occur
due to:
●
●
the gas supply system not capable of withstanding the
resulted increase in gas pressure;
evaporation of the solvent (acetone in general) for storing
acetylene in the gas cylinder by the heat, causing damage
to the gas hose and blowpipe and change in composition
of the fuel/oxidant mixture for the flame.
This guidebook presents the safe practice in gas welding and
flame cutting with the commonly used oxy-acetylene flame. The
safe practice is also applicable to welding and cutting with flames
using other fuel gases such as propane (commonly known as
'liquefied petroleum gas' or 'LPG') and hydrogen. It is intended to
provide proprietors, managers, safety personnel and supervisors
of industrial undertakings general guidelines in protecting people
at work from the hazards of gas welding and flame cutting, and in
reducing the injuries and damage caused by fires and explosions.
1
18
13. Unsafe Acts
2. Fire and Explosion Hazards
Many serious accidents have occurred in the industry due to
misuse of oxygen, gas decanting and warming up gas cylinders.
These are unsafe acts.
Fire and explosion hazards of gas welding and flame cutting are
mainly due to problems with the gas supply system, or due to the
high temperature of the flame used or the hot slag produced in
◆
the process. These hazards include:
Misuse of oxygen
Explosion may occur when oxygen contacts combustible
materials. Never use oxygen to:
● provide a source of pressure or a substitute for
compressed air, such as to clear blockages in pipelines,
●
●
●
◆
◆
fuel gases or oxygen into the atmosphere from leaks at joints,
hose connections or fittings of the gas supply system;
◆
to power air-driven tools;
blow-down clothing, equipment or work areas to remove
dust, etc.;
ventilate a confined space instead of air; or
sweeten the air of any work area or space.
as oxygen is charged into an acetylene cylinder.
Fires and explosions in the gas supply system caused by
●
flashback from the blowpipe due to gas lines not
completely purged before lighting up, or back-feeding of
fuel gas into the oxygen line or vice versa;
●
decomposition or detonation of acetylene in the absence
of oxygen or air due to flashback at the blowpipe or
overheating of gas cylinder;
Gas decanting
Recharging gas cylinders by connecting them to other
cylinders or a gas supply (known as gas decanting) is
extremely dangerous. Explosion may occur if
● the gas line or its connections or the gas cylinders cannot
withstand the high pressure during decanting;
● the decanting involves mixing of incompatible gases, such
Fires and explosions resulted from the release of flammable
●
high-pressure oxygen (without fuel gas) which promotes
combustion of materials such as oil, grease, organic
compounds, aluminium metal and its alloys, and
elastomers used in valve seats and seals;
◆
Explosions from over-pressurisation of the gas supply system;
◆
Fires from the ignition of flammable or combustible materials
in the vicinity by the flame of the blowpipe, hot surfaces of the
workpiece or hot slag from the process.
17
2
3. Health Hazards
12. Instruction and Training
Health hazards of gas welding and flame cutting are mainly due
to the radiation and toxic fumes or gases emitted during the
process. These hazards include:
◆
Eye injuries
●
●
heat cataract caused by infra-red radiation from molten
All personnel involved in gas welding and flame cutting operations
should be fully instructed and trained on the safety and health
aspects of the work under normal operation as well as in case of
emergency. The instruction and training should appropriately
cover:
metal, resulted in not able to see things clearly;
◆
hazards in gas welding and flame cutting;
arc eye caused by ultra-violet radiation emitted during
◆
selection and use of the appropriate equipment for the
the process, resulted in very painful and watery eyes;
●
foreign particles e.g. slag and cutting sparks;
◆
Skin irritation and reddening due to over exposure to radiation;
◆
Inhalation of fumes or gases produced during the process
●
◆
◆
the role of the safety devices and their limitations;
◆
selection and use of the ventilation system and personal
protective equipment and their limitations;
metal fume fever which is a febrile illness due to freshly
formed metal oxide fumes;
◆
safe operating procedures;
●
toxic fumes of metals such as lead, cadmium, beryllium;
◆
emergency procedures;
●
toxic gases such as oxides of nitrogen, fluorides resulted
◆
other aspects specific to the operation such as
in bronchial and pulmonary irritation;
◆
operation;
other injuries such as corneal ulcer and conjunctivitis from
Burns from the blowpipe flame, hot slag or hot surfaces of
●
manual handling operation of large workpieces,
the workpiece;
●
safe operation during working at height or in confined
Personal injuries due to handling gas cylinders or large
spaces.
workpieces.
3
16
◆
Fires involving acetylene cylinders are always best dealt with
by firemen from the Fire Services Department. However, the
following initial response may be appropriate:
● cool the cylinder by spraying with water only if it is safe to
do so;
●
●
close the cylinder valve to control the fire only if it is safe
to do so;
evacuate the building by activating the fire alarm or by
any other means.
Never attempt to move an acetylene cylinder that has
been involved in a fire, or move one which has been
affected by heat from a nearby fire even if it appears
to have been cooled down. Moving the cylinder may
lead to explosion!
4. Gas Supply System and
Associated Safety Devices
In general, each one of the two gases (the fuel gas and oxygen)
used in gas welding and flame cutting is supplied from a single
gas cylinder. Other methods of supply may be from a number of
gas cylinders connected by a manifold, or from a bulk supply
installation. Each gas is supplied through a flexible hose to the
blowpipe where the fuel and oxygen are mixed in an appropriate
proportion and combusted to form the required flame for welding
or cutting.
For distinguishing between the fuel gas and oxygen supplies, the
gas cylinder and hose for each gas should be appropriately
coloured. Other safety devices necessary for reducing the risk of
fire and explosion in the gas supply system include:
◆
Pressure regulator and pressure gauges to control and
monitor the pressure of the gas supply;
◆
Non-return valve at each gas inlet of the blowpipe to prevent
back-feeding of oxygen to the fuel line and vice versa;
◆
Flashback arrester (flame arrester) incorporating pressure or
temperature cut-off valve to prevent propagation of flashback
from the blowpipe and gas hoses into the gas cylinders.
15
4
Typical equipment for gas welding and flame
cutting using oxy-acetylene flame
Emergency procedures should be established which workers
should follow if a situation presenting serious and imminent danger
arises. The procedures should include guidance for the workers
explaining when and how they should stop work and move to a
safe location, or even fully evacuate the workplace. Actions for
pressure regulator
with pressure gauge
nozzle
flashback
arrester
11. Emergency Procedures
flashback
arrester
cylinder
valve
dealing with some of the possible emergency situations in gas
welding and flame cutting are listed in the following:
◆
If there is a sustained backfire in a blowpipe,
● first close the oxygen valve of the blowpipe, followed by
the fuel valve and then close both cylinder valves;
● investigate the cause and rectify the fault;
●
blowpipe
◆
non-return
valve
If there is a flashback into the hose and equipment, or a hose
fire or explosion, or a fire at the gas regulator connections,
● isolate the fuel gas and oxygen supplies by closing the
●
●
flexible hose
（acetylene - red）
（oxygen - blue）
acetylene
cylinder
（maroon）
5
re-light the blowpipe only after it is completely cooled
down.
cylinder valves only when this can be done safely;
may attempt to control the fire by fire-fighting equipment
only when there is no undue risk of personal injury;
activate the fire alarm and call for the Fire Services
Department.
oxygen
cylinder
（black）
14
such as the aggressive nature of the working environment.
Defective or damaged equipment should be taken out of
service immediately and repaired by competent person if
applicable. The regular examination of equipment should
include checking for the following defects:
arresters, resulted in low gas flow rates;
Fuel gases and oxygen are commonly stored under pressure in
gas cylinders. Fuel gases such as acetylene, hydrogen and
propane are flammable. Moreover, acetylene is potentially unstable
and may decompose violently in the absence of oxygen or air.
Safe practice in storing and handling gas cylinders includes the
following:
incorrect operation of non-return valves, resulted in
◆
●
internal gas leakage in pressure regulators;
●
incorrect operation of pressure gauges;
●
build-up of deposits of combustion products in flashback
●
5. Safe Storage and Handling
of Gas Cylinders
reverse flow not shutting off;
●
defective blowpipe such as internal gas leakage,
blockage at the nozzle.
◆
◆
◆
◆
◆
13
Ensure that gas cylinders upon receipt are appropriately
coloured and correctly labelled, and have no sign of gas
leakage.
Store gas cylinders in a cool and well-ventilated place, away
from any heat or ignition source, and keep cylinders in use
away from the welding and cutting work.
Always keep gas cylinders in an upright position and securely
anchored to strong supports, no matter during storage or when
in use.
Keep the quantity of gas cylinders under storage to a practical
minimum and in compliance with the requirements under the
Dangerous Goods Ordinance.
Handle gas cylinders with care and do not throw or bump the
cylinders heavily. Inform the supplier immediately if the gas
cylinder is found to be physically damaged.
Move gas cylinders on wheeled trolleys designed for the
purpose and securely fasten the cylinder to the trolley during
movement to prevent damaging the cylinder valves and to
minimise the risk of injury.
6
6. Fire Prevention and Protection
In gas welding and flame cutting, fires may arise from ignition of
flammable or combustible materials not only by direct contact with
the flame, but also by contact with the hot slag or workpiece which
may take a considerable time to cool down. The following
precautions are necessary to prevent fires:
Move all flammable or combustible materials to a safe place
away from the work area. Use suitable means to protect
combustible materials that cannot be moved from close
contact with flame, heat, hot slag or sparks such as covering
with fire resistant materials.
◆ Use suitable means to prevent slag or spark from reaching
combustible materials along or down ducts, channels and
through holes in walls and floors, such as covering the
openings by fire resistant materials.
◆ Prevent equipment for gas welding and flame cutting from
being contaminated with oil or grease.
◆ Before starting welding or cutting work on used containers,
ensure that the container is free from any substance that may
emit flammable or toxic vapours upon heating by washing
with suitable solvents and purging with inert gas.
◆ Provide suitable fire-fighting equipment such as fire
extinguishers, buckets of sand near by the work area.
◆ Ensure that sparks and slag from the work are extinguished
◆
and cooled before leaving the work area.
7
10. Equipment Checking and
Maintenance
◆
Pre-use equipment check
Each time before starting a welding or cutting operation, it is
necessary to check that equipment and safety devices are
correctly installed and in good working condition. Pre-use
equipment check includes:
●
●
●
●
ensuring that each gas cylinder is fitted with regulator of
the correct type and is correctly connected to the
blowpipe;
checking for defective or damaged hoses such as cuts,
cracks and abrasion; replacing or repairing the hose by
a competent person if necessary;
checking all gas line connections for leakage by using
soapy water;
ensuring that the routing of the gas hoses will not cause
severe bending of the hose or will not be run over by
other heavy equipment so as to prevent gas flow being
obscured or hose being damaged.
◆ General examination and maintenance of equipment
In addition to the pre-use equipment check, all the equipment
should be regularly examined for defects and malfunctions.
The frequency of examinations depends on the frequency of
use of the equipment and the conditions in which it is used
12
◆
◆
After the operation
● Extinguish the flame of the blowpipe.
● Close the gas cylinder valves for both fuel gas and oxygen.
● Ensure that slag, sparks and workpieces have been
completely cooled down before leaving the work area.
Operation in a confined space
Special precautionary measures should be taken to protect
the workers at work when gas welding or flame cutting is
carried out in a confined space. The likelihood of
accumulating gas from leakage is greater and hazards from
welding fumes are more significant.
● Adopt a permit-to-work system, and comply with the safety
●
●
requirements for working in a confined space.
Provide a system for fresh air ventilation and fume
extraction, and supply air type respirators to all workers
working in a confined space.
Do not take gas cylinders into a confined space whenever
practicable. If it is necessary to do so, keep the number
and size of gas cylinder taken into a confined space to a
minimum and remove them when work stops.
11
7. Health Protection and Ventilation
The risks of burns and injuries due to radiation and manual handling
operations during gas welding and flame cutting are minimised
by using appropriate personal protective equipment and safe work
procedures. Health hazard due to the hazardous fumes or gases
emitted during the process should first be reduced by provision
of suitable engineering control
ventilation.
Ventilation provides a means to remove hazardous fumes and
gases emitted during the process and to supply fresh breathing
air for the workers. The type of ventilation required should be
assessed according to the workplace environment, the volume of
the work and the toxicity of the fumes or gases emitted during the
process. Toxic fumes include those derived from metals such as
lead, cadmium, beryllium and zinc.
◆
General ventilation
General ventilation (preferably by mechanical means) is
adequate for infrequent and short duration welding and
cutting work, not emitting toxic fumes performed in the open
air or in large well-ventilated workshops.
◆ Local exhaust ventilation
Local exhaust ventilation is required for welding or cutting
operation that involves heavy in-door production work or
emits toxic fumes or gases. The local exhaust hood should
be placed as close as possible to the work for effective
removal of the toxic fumes.
8
8. Personal Protective Equipment
◆
Eye protection
Welding and cutting of metals by means of oxy-acetylene
flame is a specified process under the Factories and
Industrial Undertakings (Protection of Eyes) Regulations.
Workers engaged in the process and other persons that
may be affected shall be provided with, as appropriate
● approved eye protectors such as goggles, visors,
spectacles, face screens;
● approved shield such as helmet, hand shield;
● approved fixed shield such as screen.
◆
Protective clothing
The main aim of protective clothing is to protect worker
against burns by the flame of the blowpipe, the hot slag or
workpiece. Appropriate protective clothing should be
selected according to the nature, volume and location of
the welding or cutting work. These include facemasks,
aprons, gloves, safety shoes and spats.
◆
Respirator
Respirator provides additional protection to the worker from
inhalation of toxic fumes, and should be used in supplement
to, but not in lieu of, the use of an efficient ventilation system.
When welding and cutting is performed in a confined space,
workers should be provided with supply air type respirators
in addition to provision of efficient ventilation.
9
9. General Safe Practices
The following safe practices provide general guidelines for
establishing safe operating procedures used in gas welding and
flame cutting operations.
◆
Preparation before commencement of the operation
● Assess the hazards of the operation to enable selection
of appropriate engineering control measures (refer to
Section 7) and personal protective equipment (refer to
Section 8). Pay special attention to specific work
conditions such as handling of large workpieces,
working at height, working in confined spaces.
● Establish safe operating procedures.
● Provide training and instructions to the workers (refer
to Section 12).
● Ensure cleanliness of the work area and that measures
have been taken to prevent fires (refer to Section 6).
● Conduct pre-use equipment check (refer to Section 10).
◆
During the operation
●
●
Wear personal protective equipment and follow safe
operating procedures.
Handle lit blowpipe with great care. Do not hang it on
a gas cylinder shroud or leave it unattended even for a
short period of time.
10
8. Personal Protective Equipment
◆
Eye protection
Welding and cutting of metals by means of oxy-acetylene
flame is a specified process under the Factories and
Industrial Undertakings (Protection of Eyes) Regulations.
Workers engaged in the process and other persons that
may be affected shall be provided with, as appropriate
● approved eye protectors such as goggles, visors,
spectacles, face screens;
● approved shield such as helmet, hand shield;
● approved fixed shield such as screen.
◆
Protective clothing
The main aim of protective clothing is to protect worker
against burns by the flame of the blowpipe, the hot slag or
workpiece. Appropriate protective clothing should be
selected according to the nature, volume and location of
the welding or cutting work. These include facemasks,
aprons, gloves, safety shoes and spats.
◆
Respirator
Respirator provides additional protection to the worker from
inhalation of toxic fumes, and should be used in supplement
to, but not in lieu of, the use of an efficient ventilation system.
When welding and cutting is performed in a confined space,
workers should be provided with supply air type respirators
in addition to provision of efficient ventilation.
9
9. General Safe Practices
The following safe practices provide general guidelines for
establishing safe operating procedures used in gas welding and
flame cutting operations.
◆
Preparation before commencement of the operation
● Assess the hazards of the operation to enable selection
of appropriate engineering control measures (refer to
Section 7) and personal protective equipment (refer to
Section 8). Pay special attention to specific work
conditions such as handling of large workpieces,
working at height, working in confined spaces.
● Establish safe operating procedures.
● Provide training and instructions to the workers (refer
to Section 12).
● Ensure cleanliness of the work area and that measures
have been taken to prevent fires (refer to Section 6).
● Conduct pre-use equipment check (refer to Section 10).
◆
During the operation
●
●
Wear personal protective equipment and follow safe
operating procedures.
Handle lit blowpipe with great care. Do not hang it on
a gas cylinder shroud or leave it unattended even for a
short period of time.
10
◆
◆
After the operation
● Extinguish the flame of the blowpipe.
● Close the gas cylinder valves for both fuel gas and oxygen.
● Ensure that slag, sparks and workpieces have been
completely cooled down before leaving the work area.
Operation in a confined space
Special precautionary measures should be taken to protect
the workers at work when gas welding or flame cutting is
carried out in a confined space. The likelihood of
accumulating gas from leakage is greater and hazards from
welding fumes are more significant.
● Adopt a permit-to-work system, and comply with the safety
●
●
requirements for working in a confined space.
Provide a system for fresh air ventilation and fume
extraction, and supply air type respirators to all workers
working in a confined space.
Do not take gas cylinders into a confined space whenever
practicable. If it is necessary to do so, keep the number
and size of gas cylinder taken into a confined space to a
minimum and remove them when work stops.
11
7. Health Protection and Ventilation
The risks of burns and injuries due to radiation and manual handling
operations during gas welding and flame cutting are minimised
by using appropriate personal protective equipment and safe work
procedures. Health hazard due to the hazardous fumes or gases
emitted during the process should first be reduced by provision
of suitable engineering control
ventilation.
Ventilation provides a means to remove hazardous fumes and
gases emitted during the process and to supply fresh breathing
air for the workers. The type of ventilation required should be
assessed according to the workplace environment, the volume of
the work and the toxicity of the fumes or gases emitted during the
process. Toxic fumes include those derived from metals such as
lead, cadmium, beryllium and zinc.
◆
General ventilation
General ventilation (preferably by mechanical means) is
adequate for infrequent and short duration welding and
cutting work, not emitting toxic fumes performed in the open
air or in large well-ventilated workshops.
◆ Local exhaust ventilation
Local exhaust ventilation is required for welding or cutting
operation that involves heavy in-door production work or
emits toxic fumes or gases. The local exhaust hood should
be placed as close as possible to the work for effective
removal of the toxic fumes.
8
6. Fire Prevention and Protection
In gas welding and flame cutting, fires may arise from ignition of
flammable or combustible materials not only by direct contact with
the flame, but also by contact with the hot slag or workpiece which
may take a considerable time to cool down. The following
precautions are necessary to prevent fires:
Move all flammable or combustible materials to a safe place
away from the work area. Use suitable means to protect
combustible materials that cannot be moved from close
contact with flame, heat, hot slag or sparks such as covering
with fire resistant materials.
◆ Use suitable means to prevent slag or spark from reaching
combustible materials along or down ducts, channels and
through holes in walls and floors, such as covering the
openings by fire resistant materials.
◆ Prevent equipment for gas welding and flame cutting from
being contaminated with oil or grease.
◆ Before starting welding or cutting work on used containers,
ensure that the container is free from any substance that may
emit flammable or toxic vapours upon heating by washing
with suitable solvents and purging with inert gas.
◆ Provide suitable fire-fighting equipment such as fire
extinguishers, buckets of sand near by the work area.
◆ Ensure that sparks and slag from the work are extinguished
◆
and cooled before leaving the work area.
7
10. Equipment Checking and
Maintenance
◆
Pre-use equipment check
Each time before starting a welding or cutting operation, it is
necessary to check that equipment and safety devices are
correctly installed and in good working condition. Pre-use
equipment check includes:
●
●
●
●
ensuring that each gas cylinder is fitted with regulator of
the correct type and is correctly connected to the
blowpipe;
checking for defective or damaged hoses such as cuts,
cracks and abrasion; replacing or repairing the hose by
a competent person if necessary;
checking all gas line connections for leakage by using
soapy water;
ensuring that the routing of the gas hoses will not cause
severe bending of the hose or will not be run over by
other heavy equipment so as to prevent gas flow being
obscured or hose being damaged.
◆ General examination and maintenance of equipment
In addition to the pre-use equipment check, all the equipment
should be regularly examined for defects and malfunctions.
The frequency of examinations depends on the frequency of
use of the equipment and the conditions in which it is used
12
such as the aggressive nature of the working environment.
Defective or damaged equipment should be taken out of
service immediately and repaired by competent person if
applicable. The regular examination of equipment should
include checking for the following defects:
arresters, resulted in low gas flow rates;
Fuel gases and oxygen are commonly stored under pressure in
gas cylinders. Fuel gases such as acetylene, hydrogen and
propane are flammable. Moreover, acetylene is potentially unstable
and may decompose violently in the absence of oxygen or air.
Safe practice in storing and handling gas cylinders includes the
following:
incorrect operation of non-return valves, resulted in
◆
●
internal gas leakage in pressure regulators;
●
incorrect operation of pressure gauges;
●
build-up of deposits of combustion products in flashback
●
5. Safe Storage and Handling
of Gas Cylinders
reverse flow not shutting off;
●
defective blowpipe such as internal gas leakage,
blockage at the nozzle.
◆
◆
◆
◆
◆
13
Ensure that gas cylinders upon receipt are appropriately
coloured and correctly labelled, and have no sign of gas
leakage.
Store gas cylinders in a cool and well-ventilated place, away
from any heat or ignition source, and keep cylinders in use
away from the welding and cutting work.
Always keep gas cylinders in an upright position and securely
anchored to strong supports, no matter during storage or when
in use.
Keep the quantity of gas cylinders under storage to a practical
minimum and in compliance with the requirements under the
Dangerous Goods Ordinance.
Handle gas cylinders with care and do not throw or bump the
cylinders heavily. Inform the supplier immediately if the gas
cylinder is found to be physically damaged.
Move gas cylinders on wheeled trolleys designed for the
purpose and securely fasten the cylinder to the trolley during
movement to prevent damaging the cylinder valves and to
minimise the risk of injury.
6
Typical equipment for gas welding and flame
cutting using oxy-acetylene flame
Emergency procedures should be established which workers
should follow if a situation presenting serious and imminent danger
arises. The procedures should include guidance for the workers
explaining when and how they should stop work and move to a
safe location, or even fully evacuate the workplace. Actions for
pressure regulator
with pressure gauge
nozzle
flashback
arrester
11. Emergency Procedures
flashback
arrester
cylinder
valve
dealing with some of the possible emergency situations in gas
welding and flame cutting are listed in the following:
◆
If there is a sustained backfire in a blowpipe,
● first close the oxygen valve of the blowpipe, followed by
the fuel valve and then close both cylinder valves;
● investigate the cause and rectify the fault;
●
blowpipe
◆
non-return
valve
If there is a flashback into the hose and equipment, or a hose
fire or explosion, or a fire at the gas regulator connections,
● isolate the fuel gas and oxygen supplies by closing the
●
●
flexible hose
（acetylene - red）
（oxygen - blue）
acetylene
cylinder
（maroon）
5
re-light the blowpipe only after it is completely cooled
down.
cylinder valves only when this can be done safely;
may attempt to control the fire by fire-fighting equipment
only when there is no undue risk of personal injury;
activate the fire alarm and call for the Fire Services
Department.
oxygen
cylinder
（black）
14
◆
Fires involving acetylene cylinders are always best dealt with
by firemen from the Fire Services Department. However, the
following initial response may be appropriate:
● cool the cylinder by spraying with water only if it is safe to
do so;
●
●
close the cylinder valve to control the fire only if it is safe
to do so;
evacuate the building by activating the fire alarm or by
any other means.
Never attempt to move an acetylene cylinder that has
been involved in a fire, or move one which has been
affected by heat from a nearby fire even if it appears
to have been cooled down. Moving the cylinder may
lead to explosion!
4. Gas Supply System and
Associated Safety Devices
In general, each one of the two gases (the fuel gas and oxygen)
used in gas welding and flame cutting is supplied from a single
gas cylinder. Other methods of supply may be from a number of
gas cylinders connected by a manifold, or from a bulk supply
installation. Each gas is supplied through a flexible hose to the
blowpipe where the fuel and oxygen are mixed in an appropriate
proportion and combusted to form the required flame for welding
or cutting.
For distinguishing between the fuel gas and oxygen supplies, the
gas cylinder and hose for each gas should be appropriately
coloured. Other safety devices necessary for reducing the risk of
fire and explosion in the gas supply system include:
◆
Pressure regulator and pressure gauges to control and
monitor the pressure of the gas supply;
◆
Non-return valve at each gas inlet of the blowpipe to prevent
back-feeding of oxygen to the fuel line and vice versa;
◆
Flashback arrester (flame arrester) incorporating pressure or
temperature cut-off valve to prevent propagation of flashback
from the blowpipe and gas hoses into the gas cylinders.
15
4
3. Health Hazards
12. Instruction and Training
Health hazards of gas welding and flame cutting are mainly due
to the radiation and toxic fumes or gases emitted during the
process. These hazards include:
◆
Eye injuries
●
●
heat cataract caused by infra-red radiation from molten
All personnel involved in gas welding and flame cutting operations
should be fully instructed and trained on the safety and health
aspects of the work under normal operation as well as in case of
emergency. The instruction and training should appropriately
cover:
metal, resulted in not able to see things clearly;
◆
hazards in gas welding and flame cutting;
arc eye caused by ultra-violet radiation emitted during
◆
selection and use of the appropriate equipment for the
the process, resulted in very painful and watery eyes;
●
foreign particles e.g. slag and cutting sparks;
◆
Skin irritation and reddening due to over exposure to radiation;
◆
Inhalation of fumes or gases produced during the process
●
◆
◆
the role of the safety devices and their limitations;
◆
selection and use of the ventilation system and personal
protective equipment and their limitations;
metal fume fever which is a febrile illness due to freshly
formed metal oxide fumes;
◆
safe operating procedures;
●
toxic fumes of metals such as lead, cadmium, beryllium;
◆
emergency procedures;
●
toxic gases such as oxides of nitrogen, fluorides resulted
◆
other aspects specific to the operation such as
in bronchial and pulmonary irritation;
◆
operation;
other injuries such as corneal ulcer and conjunctivitis from
Burns from the blowpipe flame, hot slag or hot surfaces of
●
manual handling operation of large workpieces,
the workpiece;
●
safe operation during working at height or in confined
Personal injuries due to handling gas cylinders or large
spaces.
workpieces.
3
16
13. Unsafe Acts
2. Fire and Explosion Hazards
Many serious accidents have occurred in the industry due to
misuse of oxygen, gas decanting and warming up gas cylinders.
These are unsafe acts.
Fire and explosion hazards of gas welding and flame cutting are
mainly due to problems with the gas supply system, or due to the
high temperature of the flame used or the hot slag produced in
◆
the process. These hazards include:
Misuse of oxygen
Explosion may occur when oxygen contacts combustible
materials. Never use oxygen to:
● provide a source of pressure or a substitute for
compressed air, such as to clear blockages in pipelines,
●
●
●
◆
◆
fuel gases or oxygen into the atmosphere from leaks at joints,
hose connections or fittings of the gas supply system;
◆
to power air-driven tools;
blow-down clothing, equipment or work areas to remove
dust, etc.;
ventilate a confined space instead of air; or
sweeten the air of any work area or space.
as oxygen is charged into an acetylene cylinder.
Fires and explosions in the gas supply system caused by
●
flashback from the blowpipe due to gas lines not
completely purged before lighting up, or back-feeding of
fuel gas into the oxygen line or vice versa;
●
decomposition or detonation of acetylene in the absence
of oxygen or air due to flashback at the blowpipe or
overheating of gas cylinder;
Gas decanting
Recharging gas cylinders by connecting them to other
cylinders or a gas supply (known as gas decanting) is
extremely dangerous. Explosion may occur if
● the gas line or its connections or the gas cylinders cannot
withstand the high pressure during decanting;
● the decanting involves mixing of incompatible gases, such
Fires and explosions resulted from the release of flammable
●
high-pressure oxygen (without fuel gas) which promotes
combustion of materials such as oil, grease, organic
compounds, aluminium metal and its alloys, and
elastomers used in valve seats and seals;
◆
Explosions from over-pressurisation of the gas supply system;
◆
Fires from the ignition of flammable or combustible materials
in the vicinity by the flame of the blowpipe, hot surfaces of the
workpiece or hot slag from the process.
17
2
◆
1. Introduction
In gas welding and flame cutting, a fuel gas is mixed with oxygen
or air in a blowpipe to produce a flame hot enough to fuse the
surfaces together, or in case of cutting hot enough for the formation
of molten oxides of the metal involved. Fire and explosion are the
hazards that may be encountered due to problems with the gas
supply system or due to the hot slag resulted from the process.
Besides, toxic fumes and radiation produced during the process
may also pose health hazards to the people at work.
Warming up gas cylinders
Warming up gas cylinders by any means in order to increase
gas flow or to extract the last bit of gas stored in the cylinder
for use is extremely dangerous. Fire and explosion may occur
due to:
●
●
the gas supply system not capable of withstanding the
resulted increase in gas pressure;
evaporation of the solvent (acetone in general) for storing
acetylene in the gas cylinder by the heat, causing damage
to the gas hose and blowpipe and change in composition
of the fuel/oxidant mixture for the flame.
This guidebook presents the safe practice in gas welding and
flame cutting with the commonly used oxy-acetylene flame. The
safe practice is also applicable to welding and cutting with flames
using other fuel gases such as propane (commonly known as
'liquefied petroleum gas' or 'LPG') and hydrogen. It is intended to
provide proprietors, managers, safety personnel and supervisors
of industrial undertakings general guidelines in protecting people
at work from the hazards of gas welding and flame cutting, and in
reducing the injuries and damage caused by fires and explosions.
1
18
Contents
14. Useful Information
If you wish to enquire about this guidebook or require advice on
occupational safety and health, please contact the Occupational
Safety and Health Branch of the Labour Department through:
Telephone : 2559 2297 (auto-recording after office hours)
Fax
: 2915 1410
E-mail
: laboureq@labour.gcn.gov.hk
Page
1.
Introduction ............................................................
1
2.
Fire and Explosion Hazards ...................................
2
3.
Health Hazards ......................................................
3
4.
Gas Supply System and Associated Safety
Devices ..................................................................
5.
Information on the services offered by the Labour Department
and on major labour legislation can also be found by visiting our
Home Page in the Internet. Address of our Home Page is http://
www.info.gov.hk/labour.
4
Safe Storage and Handling of Gas
Cylinders ................................................................
6
6.
Fire Prevention and Protection ...............................
7
7.
Health Protection and Ventilation ...........................
8
8.
Personal Protective Equipment .............................
9
9.
General Safe Practices .......................................... 10
10. Equipment Checking and Maintenance ................ 12
11. Emergency Procedures ......................................... 14
12. Instruction and Training ......................................... 16
13. Unsafe Acts ............................................................ 17
14. Useful Information .................................................. 19
19
A Guide to Safety and Health at Work for
Gas Welding and Flame Cutting
Occupational Safety and
Health Branch
Labour Department
Occupational Safety and Health Branch
Labour Department
4/99-1-B59