Part 1 (Section 1-5)

6. WELDING AND CUTTING

A. Introduction

Welding is a common work process in industrial operations for joining metals by the application of a sufficient amount of heat. Metals can also be cut into pieces by applying similar heat processes.

There are  many different types of welding and cutting processes, but the two most commonly used in industrial operations are gas welding and electric arc welding.

This section sets forth the safety precautions for gas and electric arc welding and cutting operations in the premises of HKUST.

B. Hazards Associated With Welding and Cutting Operations

The principal hazards associated with gas welding are fire, explosions, burns, eye damage, heat stress, respiratory disease and systemic poisoning. Additional hazards which may result from arc welding are electric shock, ultra-violet radiation, and ozone.

1. Fires and Explosions
   • When any type of welding equipment is used, the naked flame, or an electric arc, provides a source of ignition for combustible materials, flammable gases or vapours. Furthermore, mishandling of gas cylinders can lead to explosions and fires.
2. Burns
   • Heat burns may result from metal spatter or from touching hot work pieces. The hands, arms, legs, feet and the eyes are particularly vulnerable.
3. Eye Damage
   • During welding operations, the eyes may be injured by sparks, spatter, slag and other foreign bodies. During gas welding, infra-red and visible light are emitted. Infra-red may dry the outer surface of the eyes which may become irritated.
   • Ultra-violet (UV) radiation, to which the eyes are very sensitive, is produced during arc welding. Excessive exposure of the eyes to UV radiation may result in conjunctivitis, photo keratitis or “welder’s flash”.
4. Heat Stress
   • Welding operations may produce sufficient heat energy to cause heat stress problems for the welder, especially when working in poorly ventilated or confined areas.
5. Respiratory Disease
   • Welding processes produce toxic gases and fumes which may result in respiratory diseases.
   • Hot metal vapour from the molten metals will produce fumes when the vapour is rapidly cooled and oxidized by the surrounding air. The fumes consist of a cloud of fine particulates which consist predominantly of oxides of the metal being used.
   • Harmful gases may also be generated during gas welding. The principle toxic gases produced are carbon monoxide and nitrous oxide fumes. Dangerous concentration of carbon monoxide may be formed in poorly ventilated areas where combustion is incomplete.
   • The high voltage arc associated with arc welding produces ozone, a gas that can irritate the respiratory system.
6. Systemic Poisoning
   • The fumes from galvanized metals, lead coatings, specially treated surfaces, and other toxic metals may affect not only the respiratory system, but also the rest of the body, particularly when the work is conducted for prolonged periods in poorly ventilated areas.
   • Welding on parts containing residues of chlorinated solvents (e.g. chlorothene VG, a degreaser fluid) can produce phosgene, a deadly nerve gas.

C. General Safety Provisions

1. Before any welding and cutting operation is carried out on HKUST premises, a Hot Work Permit must be obtained in accordance with the “Procedures for Hot Work On University Premises”. Workshop areas designated for welding operations are exempted.

2. Appropriate provisions stipulated in Chapter 6 “Fire Safety” should also be observed.

3. All persons involved in welding and cutting operations should be fully trained and aware of the hazards involved.

4. Welding and cutting operations MUST NOT be conducted near unprotected plant and vessels which contain flammable liquids or gases. For plant and vessels containing flammable liquids, all traces of flammable contents, such as oil-impregnated scale or flammable vapour, must be removed completely before any hot work is carried out. They should not be refilled until the metal has cooled down. The same is required for other chemical storage vessels.

5. A competent person should be appointed to undertake periodic maintenance, examination and repair of welding equipment.

6. Sufficient ventilation should be provided when welding operations are carried out. Local exhaust ventilation should be provided when a high concentration of welding fumes is anticipated. Ventilation should be so arranged that the welding fumes are drawn away  from the breathing zone of the welder.

7. Articles which have just been welded should not be left unattended while they are still hot. Warning signs should be posted as appropriate.

D. Gas Welding and Cutting

The Process

In gas welding, metal fusion is achieved by the use of very high temperature flames produced by a mixture of gases at a torch or blowpipe. The gases involved are oxygen and a fuel gas, such as acetylene or LPG.

Gas Characteristics

a. Oxygen

Oxygen has no smell and is not itself flammable, but it is a very good supporter for combustion. As such, excessive oxygen in the atmosphere can be extremely dangerous. Substances such as oil and grease normally do not burn without a source of ignition. However, these substances may burst into flame in the presence of a high concentration of oxygen. Oxygen level in the atmosphere should not exceed 25%.

b. Acetylene

Acetylene is highly flammable and can form an explosive mixture with air or oxygen. Storing acetylene under high pressure in its gaseous state is extremely dangerous. Therefore, acetylene is stored in solution of acetone inside the cylinder. The cylinder is also filled with a porous filler mass to ensure that there are no free spaces in which acetylene gas can be present. Acetylene should never be used or compressed in a free state at pressures higher than 15 psi, otherwise an explosion may result.

Safety of Equipment

a. Gas Cylinders

• Gas cylinders should be properly stored. They should be promptly returned to approved dangerous goods stores when not in use. Oxygen cylinders must never be stored with fuel gas cylinders.
• Cylinders should be protected against direct sunlight and heat.
• Empty cylinders should be marked as such, but they should be treated as if they are full in all other respects.
• Acetylene cylinders must always be kept in an upright position.
• Cylinders should not be allowed to stand freely. They should be properly secured by means of racks, chains, etc., to prevent them from tipping.
• Care must be taken when transporting gas cylinders. When the cylinders have to be moved frequently, they should be transported on a suitable trolley.
• If cylinders have to be handled by means of a crane, they should be secured in a special carrier before being lifted. An ordinary chain sling should not be employed directly on cylinders.
• Gas cylinders must be treated with care and be protected against mechanical damage, falls, or excessive heat.
• Cylinders must never be used to support loads.
• When not in use, cylinder heads should be protected with caps to prevent damage to the valves.

b. Regulators and Fittings

• Cylinder valves and all other connecting parts should be kept free from oil and grease.
• Cylinder valves should be firmly closed when they are left unattended for a long time (e.g., at the end of the day or a work shift).
• Valves of empty cylinders should also be closed to prevent contaminants from getting into the cylinder.
• Blow out the cylinder valves for about one second to expel any dust or debris before attaching the regulators to the cylinders.
• Only the type of regulator designed for the gas being used should be fitted to the cylinder.
• The adjustment screw of the regulators must always be released before the cylinder valve is opened, and this should be done slowly. Stand to one side of the regulator before opening the cylinder valve. The bonnet of the regulator is the weakest part which may be blown out in an accident.
• A flashback arrestor should be fitted to the regulator outlet in the acetylene line to avoid accidental flashback. A second flashback arrestor in the oxygen line will give additional safety.
• Cylinder valves should be operated by using standard keys. Long leverage spanners or keys fitted with extension pieces should not be used. Excessive force should be avoided in closing valves.
• Fittings made of copper or copper-rich alloys should not be used for acetylene gas. A dangerous explosive substance may be formed when acetylene is in contact with copper.
• The pressures of oxygen and acetylene should be the same to prevent the risk of mixing of gases inside the hoses.

c. Blowpipes

• Blowpipes should be regularly checked to ensure that they are clean and in good working condition. Hose couplings, connections and  valves should be inspected for leaks at the beginning of each shift.
• Repairs to blowpipes should only be done by the manufacturers or firms specializing in this type of work.
• Before lighting the blowpipe, purge the oxygen and fuel gas passages individually in order to expel foreign gases. Regulator pressure can be set while the gas is flowing.
• Light the fuel gas before opening the oxygen valve on the torch.
• Blowpipes should be lit using proper means such as a friction lighter, stationary pilot flame. Never use matches, cigarettes, or cigarette lighter for this purpose.
• Clogged blowpipe tip should be cleaned with suitable appliances designed for this purpose.
• The manufacturer’s recommended pressure for the blowpipe must never be exceeded.

d. Hoses

• The hoses used for gas welding and cutting must comply with the appropriate standards.
• Hose lines for different gases should be of different colours. According to BS 5120, red hose should be used for acetylene and hydrogen, orange hose for propane or other LPGs, and blue hose for oxygen.
• Hoses should be securely attached to the connections by means of suitable clips.
• Supply hoses should be so arranged that they do not pose any tripping hazards, or will not be damaged by vehicles or other moving objects.
• Hoses of equal lengths should be used for oxygen and the fuel gas.
• Hoses should be of sufficient length for the necessary manoeuvring of the blowpipe. A sudden jerk or pull on the hoses may cause the blowpipe to be pulled out from the operator’s hand, cause a gas cylinder to fall over, or a hose connection to fail.
• Hoses should be inspected frequently to ensure that there are no cuts or cracks. If defects are found, the hose should be replaced without delay.
• Naked flames should never be used for leak testing. Proper leak test solution should be used.
• Compressed air should not be used to purge any hose since it may contain oil residue from the air compressor.

 

4. Specific Hazards

a. Flashback

A flashback is a very dangerous occurrence in gas welding which is caused by mixing and burning of the gases inside a hose. Such mixing of the gases usually occurs when the hoses have been disconnected from regulators and/or blowpipes, or when new hose is being used for the first time. Sometimes it is due to loose connections. A fire or an explosion may occur when a flashback occur.

Preventive measures for flashback:

• A flashback arrestor should be fitted at the regulator outlet in the acetylene line to avoid accidental flashback. A second flashback arrestor in the oxygen line will provide additional safety.
• Ensure all connections are tight.
• Ensure cylinder valves are open and blowpipe valves are closed.
• Set regulators to the required pressure.
• Purge each hose separately and consecutively by opening the blowpipe valve and allowing gas to flow for sufficient time to ensure that only pure gas remains in the hoses. Close the valve for each gas after the exercise is complete. This exercise should only be carried out in open air or in well ventilated areas.

b. Heated Cylinder

When an acetylene cylinder is accidentally heated or becomes hot due to internal decomposition, the following steps should be taken if safe to do so:

• Remove any external source of heat.
• Shut off valves, detach regulator and other fittings.
• Drag the cylinder to an open space and keep applying water until the cylinder becomes cool (immerse the cylinder in water if possible).
• Fully open the cylinder and keep applying water until cylinder is empty. The area should be cleared of other personnel.
• Contact the suppliers for advice and request them to remove the cylinder.

E. Electric Arc Welding and Cutting

The Process

In electric arc welding, the arc is struck between an electrode and the work pieces. The temperature attained by the welding arc is approximately 4000 ^oC. At this temperature, the work pieces are melted and fused together.

Safety of Equipment

1. Welding Transformers

• All welding transformers should be designed, constructed, protected and maintained in a way that prevents electrical hazards.
• All exposed conductive parts of a transformer should be properly grounded.
• The primary (input) terminals of a transformer should be properly insulated and protected to prevent electrical hazards.
• The secondary (output) terminal of a transformer should be shrouded by insulating sleeves of sound construction and design.
• Routine maintenance, including insulation testing, for the arc welding and cutting equipment should be carried out regularly.

2. Welding Circuit

• A proper welding return should be provided and its cross-section should not be less than that of the welding lead. The return lead should be securely bonded to the work piece.
• Bare conductors should not be used as welding leads or welding returns.
• The work piece should be effectively grounded and the conductor forming the work piece earth should be of at least  16 mm cross-section and of sufficiently low impedance. It should also be protected from mechanical damage and inadvertent disconnection.
• All cable connections should be clean and tight. Cable connectors should be used.
• All cables should be of the correct type and current-carrying capacity. They should be routinely examined for defective insulation.
• Trailing welding cables should be kept clear of walkways and be protected against mechanical damage using coverings or by securing to overhead fixture. They should be properly laid to prevent tripping hazards.

3. Welding Electrode Holders

• A fully insulated electrode holder of correct rating should always be used.
• When not in use, the holder should not be placed on metal objects. It should be hung up so that it is clear of any nearby metal objects, or placed on a wooden or non-conducting surface.
• The welding cable should be properly connected to the holder.
• The electrode holder should be properly maintained to prevent damage to the insulating material.

Safety Precautions during Electric Arc Welding Operation

• Insulating gloves should be worn when an electrode is inserted into or removed from a holder.
• Welders should avoid:
• allowing any part of their body to complete an electric circuit;
• touching any electrically live parts with wet or damaged clothing, gloves or boots.
• Welding equipment should not be left unattended with the current switched on.
• When welding work is finished, the electrode should be removed from the holder and the power supply should be switched off.
• When welding is carried out on a damp place, an insulated mat should be used, or rubber boots should be worn.
• Appropriate welding current ratings should be used for specific types of welding electrode. The supplier’s instructions should be followed in making the choice.
• Electric-arc welding generates very strong UV light. The welding operation must be properly enclosed by appropriate fences to protect people in the vicinity from being harmed by the strong UV light emission.

Work in Confined Spaces

Welding and cutting operations in confined spaces should be avoided as far as practicable. If welding and cutting work in a confined space is unavoidable, the following safety precautions must be strictly followed:

• Without prejudice to the safety precautions mentioned below, the requirements stipulated in the Factories and Industrial Undertakings (Confined Spaces) Regulations must be followed.
• Appropriate pre-entry screening procedures for safe entry of confined spaces must be performed.
• Sufficient ventilation arrangement must be arranged.
• The surrounding work atmosphere must be constantly monitored with appropriate gas detection equipment.
• Cylinders should not be taken inside the confined space to avoid the risk of gas leakage through the cylinder connections or regulators.
• Welding equipment must be withdrawn during work breaks to prevent the possible build-up of gases leaking from the equipment.

Personal Protection

Chapter 13 of this Manual describes the proper selection and use of appropriate personal protective equipment.

1. Eye Protection

1. The proper type of eye protectors must be worn by welders when carrying out welding operations.
2. Eye protectors for welding operations should comply with BS 1542 and BS 679 or equivalent standards. Ordinary sun glasses do not provide adequate protection in welding operations.
3. Persons working in the vicinity of arc welding are at risk of exposure to UV radiation. Screens should be placed around the welder's work area to protect persons nearby from UV exposure.

2. Respiratory Protection

1. Adequate local exhaust ventilation should be provided for welding and cutting operations to prevent welders and people nearby from inhaling excessive harmful gases or fumes.
2. When there is a possibility of inhaling gases or fumes, appropriate respirators should be worn by the welder and other persons in the area who may be affected. However, respirators should not be used as a substitute for effective ventilation.

3. Body/Skin Protection

1. Clothing and gloves with sufficient electrical insulating capacity should be worn by the welder when carrying out electric arc welding and cutting operations in order to avoid electrocution.
2. Gloves with sufficient thermal insulation capacity should be worn when handling hot objects.
3. Light-coloured and long-sleeve clothing should be worn to guard against UV radiation from the electric arc welding process.

4. Hearing Protection

Certain types of welding and cutting operations, such as plasma welding, will create loud noise which can cause hearing loss. Proper types of ear muffs or ear plugs should be worn by the welders.

 

7. PRESSURE SYSTEM

Introduction

The sudden or uncontrolled release of pressure can cause severe injury and/or property damage.

This section describes the hazards and discusses appropriate safety precautions and requirements to avoid accidents associated with pressure systems.

Pressure Containers

There are many kinds of pressure containers, ranging from aerosol cans, boilers, air receivers, gas cylinders, hydraulic lines, etc. Once pressurized, pipes, hoses and equipment will also become “pressurised containers”.

Hazards

The hazards involved in the use of pressure systems are primarily those relating to over-pressure, over-temperature, induced vacuum, inadequate safety device, or improper operation etc. These types of conditions can cause pressure containers to rupture with explosive force that can result in serious injury and/or property damage. The weakest points of pressure containers are usually at the joints, covers, seals or relief devices. Corrosion or physical defects in the system may also create a weak point in the container.

A leak in an unrestrained container may create sufficient force from the released gas to set the container in motion. For example, a broken valve fitting on a pressurized gas cylinder can propel the cylinder like a missile, the momentum of which can drive the cylinder through a wall. A sudden release of materials under pressure may produce a shock wave capable of knocking people or objects down or causing other damages. Furthermore, flying materials can also cause injuries and damage.

Leaking materials may have dangerous properties inherent to their physical, toxic or reactive characteristics. Contact with hot water or high pressure steam will cause thermal burns. Corrosive or toxic materials such as caustics or acids may cause chemical burns or poisoning.

Improper operation of pressure systems can also be hazardous. Incorrect activation or deactivation of pressure systems can induce vacuums or impart other pressure differentials that may result in explosions or implosions.

Statutory Control

There are two major sets of ordinance controlling the safe use of pressure systems in Hong Kong:

The Boilers and Pressure Vessels Ordinance

This ordinance controls the safe use of boilers and pressure vessels. Under the ordinance,

A boiler refers to any closed vessel in which for any purpose steam is generated under pressure greater than atmospheric pressure and also means any economizer used to heat water being fed into any such vessel that is wholly or partly under pressure when steam is shut off, and any vessel in which oil is heated at a pressure greater than atmospheric pressure.

Pressure vessel means an air receiver, a steam receiver and a portable gas generator.

Before a boiler or a pressure vessel is put into use, it has to be certified by a government appointed examiner and registered under the requirements of the ordinance. The boiler or pressure vessel will have to be periodically examined and certified by a government appointed examiner when it is being put into use.

The certification and registration and the subsequent periodic examination of boilers and pressure vessels at HKUST  may be coordinated through appropriate supporting units.

Documents on design and manufacturing of boilers and pressure vessels should be obtained from the manufacturers or suppliers for the necessary certification and registration process.

Dangerous Goods Ordinance

This ordinance controls the storage and use of compressed gas cylinders which are classified as Category 2 dangerous goods under the ordinance.

The safety measures and practices associated with storage, handling and use of compressed gas cylinders are described under separate headings below.

General Safety Measures

Operational safety procedures (OSP) with appropriate risk assessments and corresponding safety control measures should be established for the operation of pressure systems (refer to Chapter 2 Section 1 Work Planning for details).

• Employees who have to work with pressure systems should be properly trained on the potential hazards and appropriate safety precautions.

• Pressurized containers should not be exposed to direct sunlight or other sources of heat to avoid pressure from building up in the containers.

• The release of pressure from containers should be controlled to prevent injuries to nearby people.

• Equipment must be de-energized and depressurized before it can be worked on. Establish and implement appropriate tag out and lock out procedures when servicing pressurized equipment.

Pressurized Fluids and Gases

Gases and liquids pressurized under pressure can be dangerous if they are not handled properly. Examples of these systems include paint sprayers, hydraulic and pneumatic tools and equipment.

Negative pressure can also be dangerous where glass utensils may be crushed or undergo implosion when vacuum is being drawn.

Hazards

Pressurized gases and fluids can cause injuries. Major hazards include:

1. Eye Injuries

Exposing the eyes to pressurized gas can lead to serious injuries.

2. Injection Injuries

Injection injuries occur when a fine stream of gas of fluid enters the body such as penetration into the skin. Fluid injected through even a tiny hole in the skin can migrate throughout several layers of tissue and is extremely difficult to remove. Injection injuries typically involve the fingers and hands, and sometimes the arms, face and other parts of the body. A gas injected under the skin may create embolisms in the blood stream that can interrupt lung or heart functions if they are allowed to migrate there.

3. Whipping of Lines

Fluid moving through a nozzle can create reactive forces on the nozzle. If the forces are large enough, they can cause the nozzle and hose to move or whip which may cause serious injuries when it strikes somebody. Likewise, this whip-like motion can cause collateral damage which could create additional hazards such as chemical spills.

Safety Measures

• Reduce the pressure of the system to a lower level if possible. Setting pressure regulators on general use air lines to 30 psi or less can minimise danger to users.

• People who work around compressed air lines, hydraulic systems and other pressurized fluid and gas equipment should have knowledge about the hazards. They should learn not to place fingers or hands against a stream and not to place the stream near anyone else. Protective gloves and clothing may help reduce injection injuries. The use of compressed air to blow away dusts or dirt on clothes or bodies is strictly forbidden.

• Workers should be clear of potential rupture points when pipelines and process equipment are undergoing pressure tests. During such tests the pressure should be increased incrementally with a brief holding period between each increase. Instruments for reading pressures should be so arranged that they are clearly visible at all times to workers who are located at a safe distance.

• Pressurized hose or lines that are unavoidably located near people should be protected with guards of sufficient strength to ensure that the hoses are adequately restrained if a leak or rupture occurs. 

• Solid lines (e.g. metal pipes) do not whip or leak as readily as flexible hoses which can develop leaks from vibration, pressure cycles and aging. Therefore, where high pressure lines must come close to people, solid lines with tight, well-maintained fittings should be used.

• When flexible high pressure lines must be used, the connections should be well-maintained and frequently examined to prevent any accidental detachment of the line, resulting in uncontrollable whipping of the line. Hose clamps with restraining chain should be fixed to minimize the whipping effect of flexible hoses should they get loose accidentally.

• Pipe lines must never be connected or disconnected when there is any pressure in them.

Safety Measures and Practice for using Compressed Gas Cylinders

Storage

• Cylinders must be stored in cool, dry and well ventilated places. Cylinders in excess of the exempted quantity must be stored in approved dangerous goods stores.

• Cylinders must be kept away from sources of ignition or excessive heat.

• Cylinders must be stored upright and secured using racks, chains and straps in order to prevent them from falling.

• Cylinders must not be placed where objects may strike or fall on them, possibly damaging the cylinders or their components.

• Cylinders must not be placed along fire escape routes.

• Incompatible gases must not be stored close together. Oxygen cylinders must be stored away from flammable gases.

• Cylinders not in use should be returned to the store.

• Cylinders should be correctly tagged “full”, “in-use” or “empty”. Cylinders should be considered empty while positive pressure (25 psig or greater) still remains, in order to prevent suck-back and contamination (i.e. never completely empty a re-useable compressed gas cylinder).

• Cylinder valve of “empty” cylinders must be closed to avoid contaminants from getting into the cylinder.

Transportation/Handling

• Cylinders should be transported with proper cylinder carts. Cylinders must be securely tied down onto the carts.

• Cylinders must be secured with chains or ropes to a cradle or platform before they are moved by crane, hoist, or forklift.

• Do not drag, roll, or slide cylinders. Cylinder valves should be protected with caps during transportation.

• Never drop a cylinder or permit cylinders to strike each other violently.

• Protect cylinders from any object that will produce a cut or abrasion in the surface of the metal.

Use

• Never accept or use a leaking cylinder.

• Cylinders must be clearly marked with the content of the gases inside. Do not rely on the colour of the cylinders for identifying their content. Confirm cylinder contents by label before using.

• Some compressed gases are more hazardous than others. Make sure that you know the hazardous properties of the content of a cylinder and the appropriate precautions in handling the gas. You can get the information by studying the Safety Data Sheets (SDS) for the gas.

• Any cylinder with a valve that cannot be opened by hand or using a manufacturer supplied opening device must be returned to the supplier. Do not use a pipe wrench, hammer, or extension rod to open or loosen a cylinder valve. Such practices can result in serious injury and/ or property damage.

• Cylinder must not be used without an appropriate regulator. Compressed gas regulators for different types of gases cannot be used interchangeably. Use only the right type of regulator for the right gas.

• Do not force fit regulators or fittings to cylinders.

• Cylinders, cylinder valves, couplings, regulators, hoses, and apparatus must be kept free of oily or greasy substances. This is especially important for oxygen cylinders. Not observing this may result in an explosion. Store and handle regulators and fittings properly to prevent contamination of oil or grease.

• Fittings and piping which contain copper must not be used for acetylene gas in order to prevent the formation of explosive compounds.

• Gases should not be mixed inside cylinders. Experimental set-up requiring such practice should include an OSP with appropriate risk assessment addressing the hazards and stipulating the controls.

• Close cylinder valves when not in active use.

• Whenever an oxidizer and a fuel gas are used (such as in gas welding), “flash back arrestor” must be fitted for each gas.

• Gaseous acetylene under pressure may decompose with explosive force. Never use acetylene gas at pressures in excess of 15 psig.

• Inspect gas cylinders regularly for obvious signs of defects, deep rusting, or leakage.

• Hoses and fittings used for connection to compressed gas cylinders must be of adequate pressure ratings.

• Hoses should be securely connected to cylinders by appropriate fixing device. Flexible hoses should be connected with proper hose clamps. Hose clamp with large contact surface should be used for clamping flexible hose on glass hose tail to prevent damaging the glass fitting.

• Never strike an electric arc or direct a flame at a cylinder, or include a cylinder as part of an electric circuit.

Proper Procedure for Opening and Shutting Down Cylinder Valves

1. Check if the proper type of regulator is fixed to the cylinder valve outlet. Check if the pipe lines and hoses are properly connected and securely clamped. Correct any discrepancies before proceeding.
2. Turn the pressure adjusting screw of the regulator counter-clockwise until it turns freely to ensure that the regulator is OFF.
3. SLOWLY open the cylinder valve until the cylinder pressure gauge on the regulator reads the cylinder pressure. DO NOT stand in front of the regulator since it is the weakest point of the system and there is a high risk of the regulator being blown off when thing goes wrong. Stand aside when opening the cylinder valve.
4. With the cylinder valve open, set the desired delivery pressure by turning the pressure adjusting screw clockwise until the desired pressure is reached.
5. Always keep the cylinder valve free of obstructions such as tools, rags, and hoses, etc. to permit easy and immediate gas cutoff.
6. When the work is finished, always turn off the cylinder valve first and then the regulator. The pressure gauges should be brought back to zero. Use the cylinder valve instead of the regulator valve for turning off the gas.
7. Before removing the regulator, make sure that the cylinder valve is closed and the pressure gauges read zero.

Implosion under Negative Pressure

Hazards

Implosion under negative pressure is another form of hazard associated with pressure. Implosions in laboratory facilities may occur when vacuum pumps, or other equipment that creates negative pressure, is used in conjunction with glass containers, or when such equipment is used in the vicinity of glass windows and viewpoints. When an implosion occurs, glass fragments may be propelled in all directions. In addition to cuts, these fragments may inject toxic, corrosive or irritant products into the body. Containers containing hazardous materials may splash onto people or cause spills during an implosion incident.

Safety Measures

• Maintain equipment in good working order, with all safety systems installed.

• Use plastic containers instead of glass containers wherever possible.

• If glass containers have to be used, protect the glass containers with plastic coating. The size of glass containers should be minimized. Adequate shielding should be set up between the glass container and people.

• Wear safety goggles and other appropriate protective equipment, such as face shields and protective clothing, when implosion hazard exists.

• Conduct experiments that have the potential for implosion inside a fume hood with the vertical sash lowered.

 

8. CONFINED SPACES

A.    Introduction

Confined space accidents are often among the most tragic cases of occupational deaths. Invisible and deadly, the hazardous atmosphere inside a confined space can often take more than one life as heroic efforts are made to rescue the initial victim.

The purpose of this section is to explain the potential hazards that could exist in confined spaces and set out appropriate safety procedures to ensure that, whenever it is necessary for someone to enter a confined space, all necessary precautions are taken against dangers resulting from the presence of noxious fumes, toxic gases, oxygen deficiency, excessive heat, humidity and other hazards that can exist in a confined space.

The relevant requirements stipulated in the Factories and Industrial Undertakings (Confined Spaces) Regulation should also be observed.　

B.     Determination of Confined Spaces

The term confined space embraces a wide range of areas, but it normally refers to those areas in which, by virtue of their enclosed nature, arise a reasonably foreseeable risk, including:

• loss of consciousness of any person inside arising from exposure to gas, fume, vapour or the lack of oxygen;
• serious injury to any person inside arising from a fire or explosion;
• loss of consciousness of any person inside arising from an increase in body temperature;
• drowning of any person inside arising from an increase in the level of liquid or other free flowing materials (e.g. mud);
• entrapment of person(s) inside.

Without limiting the generality of the above definitions, the following areas can be regarded as typical confined spaces:

• A completely enclosed structure with limited access through a manhole (e.g. storage tank, boiler, pressure receiver and vessel).
• A structure or vessel of such a depth as to require special means of entry, with its top usually open e.g. chamber, tank, vat, pit, well, caisson, vault, bin, silo and shaft.
• A structure or ducting of sufficient length with inadequate cross-ventilation e.g. tunnel, pipeline, flue, duct and sewer.
• A room or enclosed area in which dangerous fumes such as toxic, flammable, explosive or corrosive fumes are present.

If there is any doubt in determining whether a particular location should be classified as a confined space, HSEO should be consulted for making the appropriate assessment.　

 

C.    Hazards of Confined Spaces

A confined space may become hazardous when one or more of the following conditions arises:

Toxic gases or fumes can build up from the toxic substances exist inside the confined space or by the work being carried out inside the confined space, e.g. use of chemicals, welding operations, operation of internal combustion engines, etc.
 

The causes for the accumulation of flammable or explosive gases or fumes are similar to those for toxic gases or fumes as described above.

Excessive oxygen concentration in the atmosphere can also be hazardous as it promotes combustion.

1. Accumulation of toxic gases or fumes
2. Accumulation of flammable or explosive gases or fumes
3. Oxygen Deficiency

The normal oxygen content in the atmosphere is 20.9 %. Oxygen content below 18 % can endanger human lives. A number of situations can lead to oxygen deficiency inside a confined space. The following are some of the typical situations:

1. oxygen is used up without adequate supply in a totally enclosed area (hot work operations will accelerate the consumption of oxygen);
2. oxidation of metal parts inside the confined space (totally enclosed ferrous tanks are especially vulnerable);
3. oxygen is displaced by heavier gases (may not be toxic) such as carbon dioxide, nitrogen, etc.;
4. oxygen inside a tank or vessel is driven out in a purging process.

4. Health hazards

5. Biological hazards, such as mold, mildew and spores, frequently found in dark, damp spaces can irritate the respiratory system.
6. Bacteria and viruses found in sewage can also threaten the body with a variety of diseases.
7. High temperature

Such hazard exists in confined spaces where the temperature inside is too high, such as a large-scale boiler or furnace. This may result in loss of conscious of the person(s) inside, or heat-related illnesses, such as heat cramp.

6. Ingress of hazardous substances

Such hazard exists in confined spaces into which substances such as chemical substances, steam or water may be discharged. Typical examples include chemical storage tanks, water tanks, etc.

7. Engulfment hazards

Engulfment hazard exists in areas where loose materials such as flour, sawdust, sand or mud, etc. are contained. When disturbed, the loose materials may collapse and bury the person(s) inside.

D.    Responsibilities

It requires the full commitment and co-operation of all parties concerned to ensure the health and safety of persons working in a confined space.

1. Management

The management should ensure that every operation in the confined space is safe and without risk to the personnel working inside, or in the vicinity of the confined space. Specific duties include the following:

1. To identify all operations to be conducted in confined spaces and the locations of those spaces.
2. To ensure that the supervisors and workers involved in any operations in a confined space are:

• adequately trained and qualified for the work.
• fully aware of the potential hazards.
• fully understand and will comply with the safety procedures set out in this section.

3. To give sufficient prior notice to HSEO for making any necessary pre-entry safety arrangements, such as the conduct of risk assessment for the confined space.
4. To take all necessary safety precautions as recommended in the relevant Risk Assessment Report prepared by a Competent Person appointed to conduct the risk assessment for the confined space.
5. To issue an appropriate "Confined Spaces Entry Certificate"  as required by the Factories & Industrial Undertakings (Confined Spaces) Regulation.

2. Employees who are assigned to work in confined spaces

Employees should co-operate with the management and HSEO in respect of the required safety arrangements, and take reasonable care for the health and safety of themselves and other persons who may be affected by his/her acts or omissions at work. As far as working in confined spaces is concerned, employees should:

1. Attend appropriate safety training courses as required by the management.
2. Follow all relevant procedures, instructions and advice established and given by the management and HSEO for safe working in confined spaces.
3. Make full and proper use of all necessary safety equipment and emergency facilities provided by the management, and report to the management any faults and defects identified.

3. The Health, Safety and Environment Office (HSEO)

HSEO is responsible for providing all necessary advice and assistance to the respective units for safe entry into confined spaces, which may include:

1. Testing and monitoring of the air condition in the confined space upon request by the concerned unit;
2. To conduct appropriate risk assessments of the confined space upon request by the concerned unit;
3. To provide or arrange for appropriate safety training for staff who need to be involved in confined spaces operations.

E.    Training and Qualifications

Employees involved in confined spaces operations have to be trained and obtain the following qualifications as appropriate:

Certified Workers

Employees who need to enter or work in a confined space have to attend an approved safety training course (note 1) and obtain a valid "Certified Worker" certificate.

Competent Person

Employees to be appointed to conduct risk assessments for confined spaces have to attend an approved safety training course (note 2) and obtain a valid "Competent Person" certificate.

Note 1: This is a one-day training course approved by the Labour Department. HSEO has obtained the approval to conduct this training course.

Note 2: This is a two-day training course approved by the Labour Department. HSEO has obtained the approval to conduct this training course.

F.    Documentations for Confined Space Operations

Confined Space Entry Request Form

This form is to be submitted to HSEO by the concerned unit indicating the date(s), location and nature of the confined space operation. Specific assistance needed from HSEO, such as performance of risk assessment, should be indicated in the Request Form. A pro forma of the request form is attached as Appendix 5D1.

Confined Space Risk Assessment Report

This report is to be prepared by a Competent Person appointed to conduct a risk assessment for operations in a confined space. A pro forma is attached as Appendix 5D2.

Confined Space Entry Certificate

This certificate is to be issued by the management of the concerned unit for the operations in a confined space to certify that the confined space is safe for entry after all necessary safety precautions in relation to the hazards identified in the Risk Assessment Report have been taken. A pro forma of the certificate is attached as Appendix 5D3.

G.    General Procedures for Safe Operations in Confined Spaces

1. When work is to be carried out in a confined space, the unit planning for the work should complete and submit a "Confined Space Work Request Form"  to HSEO, giving sufficient time in advance for HSEO to make the necessary pre-entry safety arrangements, such as risk assessment, air monitoring, etc.
2. The unit should arrange for a risk assessment to be conducted by a Competent Person on the working conditions in the confined space with recommendations on measures to be taken in relation to safety and health of workers while working in that space. The risk assessment can be conducted by a Competent Person in the unit, or assistance can be sought from HSEO for the assessment. An appropriate "Risk Assessment Report" should be prepared by the Competent Person and submitted to the management of the unit.
3. Upon receiving the "Risk Assessment Report" from the Competent Person, arrangements should be made by the unit to comply with all recommendations made in the report.
4. A "Confined Space Safe Entry Certificate" should then be issued by the unit stating that all necessary safety precautions in relation to the hazards identified in the Risk Assessment Report have been taken. The period during which workers may remain safely in the confined space should be stated in the certificate.
5. Only "Certified Workers"  are allowed to enter or work inside a confined space.
6. The Risk Assessment Report and the Safety Entry Certificate should be posted at the entrance of the confined space for easy reference.
7. When the work is being undertaken in a confined space, a person has to be posted outside the confined space to maintain communication with the workers inside. The person posted at the outside has to be a "Certified Worker" and familiar with the emergency procedure for confined space operations.
8. The Safe Entry Certificate should be properly cancelled with HSEO when the works in the confined space have been completed and all persons have got out of the confined space.

H.    Specific Procedures for Special Work Conditions

Depending on the nature of risk and the existence of appropriate hazard control installations, specific entry procedures have been established for certain work sites. The respective procedures should be followed when working in those areas. The established "specific procedures" are listed in Appendix 5D4 and attached to as follows: 

• Entry Procedures for Underground Pump Rooms
• Entry Procedures for Main Building Service Tunnel
• Entry Procedures for Sewage Tunnel
• Entry Procedures for Sea Water Pump House/UG2 Service Tunnel
• Entry Procedures for Routine Cleaning/Maintenance/Repair

I.    Emergency Procedures

1. Security Control Centre (SCC) must be informed before any confined space entry.
2. When work is being carried out inside a confined space, a person (the attendant) must be posted at the entrance of that confined space. The attendant must be a “Certified Worker” or “Competent Person”.
3. The attendant stationed outside must communicate closely with the persons staying inside the confined space and to watch out for any abnormal conditions.
4. Persons inside the confined space should stay alert and watch out for any abnormal changes in the environment and in their health conditions, such as smell of gas, feeling of dizziness, etc. They must evacuate the confined space immediately and report the situation to their supervisor or seek help from the SCC. They must also warn all other persons inside the confined spaces about the situation and ask them to leave.
5. In the event that someone is overcome inside the confined space, the attendant stationed outside must immediately call SCC for assistance. He/she must not enter the confined space to exercise rescue without wearing a proper breathing apparatus set and without ensuring that there is no other imminent dangers in the confined space.
6. When informed of an emergency, the Security Duty Controller should make sure that he has obtained the necessary information regarding the emergency. He should then immediately call the Fire Services Department for assistance if necessary. At the same time, he should dispatch a team of adequate number of Security personnel to the scene to provide assistance. The Security personnel dispatched should have adequate knowledge about the hazards in confined spaces. They should also bring with them the necessary rescue equipment, including safety harnesses and lifelines, resuscitators and SCBA, etc.
7. Before entering a confined space for the rescue attempt, appropriate gas detection equipment must be used to verify the atmospheric conditions so that appropriate safety measures can be determined for the rescue and for the safety of the rescuer.
8. HSEO should also be informed of any emergencies concerning with confined spaces entries.