Fire and Safety course in Delhi Lucknow Patna

On completion of this element, you should be able to demonstrate understanding of the content by applying what you have learnt to familiar and unfamiliar situations. In particular you should be able to:

 Describe the principles of fire initiation, classification and spread.

 Outline the principles of fire risk assessment.

 Describe the basic principles of fire prevention and the prevention of fire spread in buildings.

 Identify the appropriate fire alarm system and fire- fighting arrangements for a simple workplace.

 Outline the factors which should be considered when implementing a successful evacuation of a workplace in the event of a fire.

KEY INFORMATION

• Three things must be present for a fire to start: fuel, oxygen and
• The five classes of fire (determined by the types of fuel) are: Class A (organic solids), Class B (flammable liquids), Class C (flammable gases), Class D (metals) and Class F (high-temperature fats). (This is under the UK system; other national or regional systems may )
• Fire can spread through a workplace by direct burning, convection, conduction and
• Fires have many different causes, but common ones are faulty or misused electric equipment, deliberate ignition, hot works, heating and cooking appliances, and smoking The consequences of workplace fires include injuries and fatalities, damage to business, and harm to the environment.

PRINCIPLES OF FIRE

The basic principles of fire and combustion can be represented by the fire triangle:

For fire to exist, three things must be present:

• Fuel – a combustible material or substance that is consumed during the combustion In a typical workplace, fuels can include paper and cardboard, wood and soft furnishings, structural materials, petrol and diesel fuels, butane, acetylene and other gases, solvents and other chemicals.
• Oxygen – consumed during combustion when it is chemically combined with the Oxygen is present in air at a concentration of 21%. During a fire oxygen can also come from other sources, including certain oxygen-rich chemicals (usually called oxidising agents), such as ammonium nitrate.
• Sources of ignition (heat) – a heat or ignition source is essential to start the combustion process. Once combustion has started it generates its own heat which is usually sufficient to keep the fire burning (in other words once the fire starts the heat source can be removed and the fire stays alight). Some examples will be described later in this 

Once a fire has started it will produce heat, a flame (the zone where oxygen and flammable vapours are chemically combining in the combustion process) and smoke. The exact composition of the smoke will vary but typically smoke is made up of hot combustion gases such as carbon monoxide (CO) and carbon dioxide (CO2) and small particles (soot).

The fire triangle is useful for two reasons:

• Fire prevention – if the three elements are kept apart fire cannot
• Fire-fighting – if one of the elements is removed the fire will go

CLASSIFICATION OF FIRES

Fires are classified into five categories according to fuel type. The classification is useful as the basis for identifying which type of fire extinguisher to use (see later). Note that the classifications shown here are those used in the UK; local classification systems may exist in other countries and regions, but the UK system provides a good example.

TOPIC FOCUS

Classification of fires:

• Class A – solid materials, usually organic, such as paper, wood, coal and
• Class B - flammable liquids, such as petrol, oil and
• Class C – gases, such as methane, propane and acetylene.
• Class D – metals, such as aluminium or magnesium.
• Class F – high-temperature fats and oils, such as cooking

Note that there is no Class E fire. This classification was avoided because of potential confusion between Class E and electricity. Electricity is not a fuel (though it can be an ignition source).

GLOSSARY

FLAMMABLE

Easily ignited by a heat source at normal ambient temperatures. The words “combustible” and “inflammable” mean the same thing.

Note that the phrases “highly flammable liquid” and “extremely flammable liquid” have technical definitions that indicate these liquids can be ignited at low ambient temperatures.

PRINCIPLES OF HEAT TRANSMISSION AND FIRE SPREAD

Once a fire has started it can spread by four different methods: direct burning, convection, conduction, and radiation. In a real fire situation all four methods may apply.

TOPIC FOCUS

• Direct Burning

The simplest method of fire spread, where a flame front moves along or through the burning material. For example, if the corner of a piece

of paper catches fire, the flame front will spread across the paper.

• Convection

The principle that hot air rises and cold air sinks. Hot gases generated by the fire rise straight up from the fire:

• Inside a building these hot gases will hit the ceiling and then spread out to form a layer underneath the ceiling. When these hot gases touch any combustible material (such as a wooden curtain pole) they may heat that material up sufficiently so that it bursts into flame.
• Outdoors these convection currents will contain burning embers that are carried on the currents until the air cools and the embers are dropped to the This is

a common way for forest fires to travel and jump over obstacles (such as roads).

• Conduction

The principle that heat can be transmitted through solid materials. Some metals, in particular, conduct heat very efficiently (e.g. copper). Any pipes, wires, ducts or services running from room to room can act as conduits for heat and spread the fire.

• Radiation

Heat energy can be radiated through air in the form of infrared heat waves, which travel in straight lines (just like light) and can pass through transparent surfaces (such as glass). Radiant

heat generated by a fire shines onto nearby surfaces and is absorbed. If the material heats up sufficiently it can burst into flames.

COMMON CAUSES AND CONSEQUENCES OF FIRES IN WORKPLACES

Causes

Fires in workplaces start for many different reasons. Some of the most common causes of workplace fires are:

• Electrical equipment – faulty wiring, overloaded conductors, misused equipment and the incorrect use of electrical equipment in inappropriate environments (see Element 5).
• Deliberate ignition – many workplace fires are started deliberately. In some cases, the workplace has been targeted, g. by a disgruntled employee or an unhappy customer. In other cases, it has not, e.g. youths playing with matches on an industrial estate.
• Hot work – any work involving the use of naked flames (e.g. a propane torch or oxy-acetylene cutting equipment), or which creates a significant ignition source (e.g. arc-welding and grinding).
• Smoking – in particular, carelessly discarded smoking materials, such as cigarette butts and
• Cooking appliances, g. fat pans left unattended.
• Heating appliances, g. electric fan heaters and space heaters, especially when left unattended.
• Unsafe use and storage of flammable liquids and gases, g. petrol, acetone and liquefied petroleum gas (LPG). Static sparks can be generated, which could ignite a flammable vapour.
• Mechanical heat – generated by friction between moving parts, such as a motor and its bearings, or cold work generating
• Chemical reactions - can also generate heat, g. oxidisers (rags soaked in oil and solvents are a fire hazard, because as the oil or solvents oxidise,

heat is replaced and there is a risk of spontaneous combustion).

Consequences

Fires cause enormous damage to buildings and building contents. Items that are not directly destroyed by the fire will often be severely affected by smoke damage. These losses will usually be covered by insurance, although the loss of business and premises are difficult to recover, leaving many people without jobs and a place of work.

Perhaps of more concern are the consequences to people. Most of the people killed in workplace fires are not killed by the flames directly, but indirectly, by smoke inhalation. Serious burns may also result.

Fire and fire-fighting can also do significant damage to the environment. Forest fires (though not a significant risk in many parts of the world) do huge damage. Fire- fighting can cause pollution because of the large volumes of contaminated water that run off the fire site into watercourses.

KEY INFORMATION

Fire risk assessment is a five-step process to:

• Identify the fire
• Identify the people at risk from
• Evaluate the risk from fire; remove or reduce the risks and protect from those
• Record the findings; plan new controls; instruct and train those at
• Review the assessment

REASONS FOR CARRYING OUT A FIRE RISK ASSESSMENT

The three main reasons for assessing and managing fire risks are to:

• Prevent harm to people – all employers have a moral duty to take appropriate steps to ensure the health and safety of their employees and other people who may be
• Comply with the law – employers have legal obligations regarding fire safety and can be penalised if they fail to meet those
• Minimise the cost of fire in the workplace – most businesses that suffer a major fire do not fully recover from its If a factory or office burns down it may never be rebuilt, costing not only the business, but also the jobs of workers based there.

Fire risk assessment can also affect the overall level of risk (risk magnitude) of a company. A higher level of risk leads to a lower chance of competitive insurance premiums, and a greater chance of harming people, attracting negative publicity and losing orders – all of which affect a company’s chances in the marketplace.

Carrying out a fire risk assessment allows a company to establish a suitable safety management system and fire safety policy so it can continue to appreciate and manage the risks from fire in the workplace, as well as assuring its business future at the same time.

FACTORS TO BE CONSIDERED IN FIRE RISK ASSESSMENT

Fire safety legislation and fire safety standards vary between countries, and from region to region. Fire risk assessment is a legal requirement in many countries (e.g. in the EU). However, some factors should be considered in

any workplace; these can best be described by applying risk assessment methods to fire safety.

There are many different methodologies for carrying out a fire risk assessment. Here we are using one very similar to the five steps of general risk assessment but with special emphasis on fire safety:

• Identify the fire hazards:
  • Sources of
  • Sources of
  • Sources of
• Identify the people who might be at risk:
  • People in the
  • Give special consideration to vulnerable
• Evaluate, identify and implement the fire precautions that are required:
  • Fire
  • Prevention of the spread of smoke and
  • Fire detection and
  • Fire-fighting
  • Means of escape.
  • Signs and
  •  
• Record findings, plan and train:
  • Emergency
  • Information and
  •  
• Review and revise the assessment as

Identify the Fire Hazards

At this stage the locations, types and amounts of the various potential fuels (combustibles) should be

considered. All workplaces will contain simple combustibles such as paper, packaging materials and furniture. Some workplaces may contain large quantities of highly flammable, or extremely flammable materials, such as solvents, fuel or gases.

Potential ignition sources, and the frequency and duration of occurrence, are also important. Hot works, electrical equipment, portable fan heaters, etc. should all be taken into account, especially heat sources that are frequently used for long periods of time and that require special attention to ensure safety (e.g. hot work).

Sources of oxygen are significant factors to consider; oxygen cylinders and oxidising substances can both act as oxygen sources that can increase the risk of a fire starting and the severity of the fire.

Identify the People Who Might be at Risk

As with a general risk assessment, consider the general groups of people who might be affected by a fire in the workplace. These might be employees, contractors working on site, visitors, or members of the public. The

number of people affected might be relatively small (e.g. 10 employees in a single workshop building) or very large (e.g. in a shopping centre).

Special consideration must be given to those who might be more at risk in a fire situation, such as:

• Lone workers (e.g. cleaners).
• Workers in isolated locations (e.g. maintenance staff in a boiler-house).
• Vulnerable groups, such as the very young (e.g. toddlers in a crèche), the elderly (e.g. residents in a care home) or the disabled (e.g. wheelchair users).

It might be acceptable in some instances to consider these people in groups, but in some cases it will be necessary

to consider their particular needs on an individual basis. For example, a disabled worker in a multi-storey building may have impaired vision or impaired mobility; these two disabilities present very different problems and require different solutions.

Evaluate, Identify and Implement the Required Fire Precautions

The risk of a fire occurring must be evaluated (as should existing precautions), as well as the risk to people. This can be done by thinking about:

• Potential fuels, ignition sources and oxygen
• Methods by which fire might
• How smoke and flames might travel in the
• The locations of the people in the
• The structural fire resistance of the building (e.g. presence of timber structures).

A range of preventive and precautionary measures will be necessary for all workplaces. These will include the following issues, which are covered in more detail in the rest of this element:

• Fire prevention – ways of minimising the risks of a fire occurring.
• Prevention of the spread of smoke and flames – ways of minimising the risk to people should a fire occur and allowing them time to evacuate the premises safely.
• Fire detection and alarm – to ensure that a fire is detected as soon as possible once it has started and that every person in the premises is then alerted to the risk.
• Fire-fighting equipment – portable extinguishers and fixed
• Means of escape – safe routes out of the premises to a place of total
• Signs and notices – to indicate the escape routes and the emergency
• Lighting – to enable people to use the escape routes safely.

All these fire precautions have to be inspected, tested and maintained in effective working order. This requires that a regime of routine checks is carried out at various frequencies. Records of these checks should be kept.

Record, Plan, Instruct and Train

The significant findings of the fire risk assessment should be recorded according to the requirements of national or local regulations. The exact nature of the record will vary depending on the nature of the workplace. The record might include a line drawing of the workplace (i.e. a plan, as seen from above) showing the various fire precautions and the means of escape.

New controls should be planned and an emergency plan developed outlining the emergency procedures in the event of a fire. In a simple workplace this may be nothing more than a fire action notice. In a larger, more complex workplace, more detailed plans will need to be made. This may require consultation and co-operation with other occupiers or controllers of the premises. Again, there are likely to be local requirements with regard to how this information is recorded.

All relevant people (including employees, contractors and visitors to the premises) should be given appropriate instruction and training on fire safety. The nature of

the instruction and training provided would vary, but should include fire prevention measures and emergency procedures.

Review

Regular review of the fire risk assessment will ensure that it stays relevant and suitable.

In particular, the risk assessment should be reviewed:

• After significant changes that might affect fire safety (e.g. a change to the fabric of a building, or the introduction of a new combustible material).
• After a fire emergency (to ensure that all precautions worked as intended).
• Periodically, to ensure that things have not been missed.

Temporary  Workplaces

Fire safety must be provided for all workers at all times. If a workplace is temporary then a fire risk assessment should be carried out and fire precautions implemented. This

is particularly the case on construction sites, where the nature of the work may mean rapid changes to the layout and nature of the workplace.

If an existing workplace is to be changed or modified in some way, and this will affect fire safety, then the fire risk assessment for those premises should be reviewed and revised as necessary. Depending on national legislation it may also be necessary to inform the fire regulation authority of the changes.

KEY INFORMATION

• Fire can be prevented by controlling potential fuel Risk from fuel sources can be managed by elimination, substitution, minimising quantities, and by safe use and storage.
• Fire can also be prevented by controlling potential ignition sources, such as electrical equipment, hot works, discarded smoking materials, and cooking and heating
• Safe systems of work can be used to control work activities involving fire risk, g. permit-to-work systems can be used to manage the risk associated with hot works. This includes ensuring good standards of housekeeping.
• Flammable liquids must be used and stored with appropriate care to minimise the associated fire
• If a fire does start within a building, structural measures will normally exist to contain the fire and smoke in one part of the This compartmentation must be maintained, and doorways should be properly protected with self-closing fire doors.
• Electrical equipment must be of a suitable category for use in an explosive

CONTROL MEASURES TO MINIMISE THE RISK OF FIRE IN A WORKPLACE

The best course of action to ensure fire safety is to prevent fires from starting. Fire prevention can be based on some simple ideas taken from the fire triangle:

• Control fuel
• Control ignition
• Control oxygen

In particular, minimise these sources and keep them physically apart.

Control of Combustible and Flammable Materials Combustible materials (such as paper, cardboard, wood and furnishings), flammable liquids (such as petrol and acetone) and flammable gases (such as butane, propane

and methane) are all potential fuels and should be stored, handled, transported and used with appropriate care if the fire risk that they represent is to be controlled.

The best option is to eliminate the combustible and flammable materials and substances entirely from the workplace. This might be done, for example, by disposing of old stocks of materials and substances that are no longer needed.

Alternatively, it may be possible to substitute one potential fuel source for another that presents less of a fire risk. For example, a petrol-powered generator might be changed to a diesel-powered one, eliminating the need to store and handle petrol. Since petrol is a highly-flammable liquid (i.e. easily ignited at lower ambient air temperatures) but diesel is not (i.e. not easy to ignite at ambient air temperatures) there is a considerable reduction in fire risk.

If combustible and flammable materials cannot be eliminated or substituted, then the quantities of these materials present in the workplace should be minimised. This requires good stock control, housekeeping and waste management. For example, cardboard is used extensively by many manufacturing companies as a packaging material. It will be stored in bulk in a warehouse. Minimising the stocks of cardboard reduces the fire risk in the warehouse.

For the combustible and flammable materials that remain arrangements must be made for safe use and storage.

For example, if liquefied petroleum gas (LPG) is present in a workplace the following arrangements should be made:

• Bottles (cylinders) should be stored
• The storage area should be fenced with a secure, lockable
• Warning signs should be
• Ignition sources should be eliminated from the
• Bottles should be kept upright and chained
• The storage area should be separate from other buildings.
• Empty and full bottles should be kept
• Oxygen bottles should not be stored with
• Only those bottles actually required should be removed from the storage area and should be returned after use.

Control of Ignition Sources

Poor control of potential ignition sources is a common cause of workplace fires.

• Electrical equipment should be routinely inspected and tested to ensure that it is This will prevent faults developing that might cause sparks or overheating. Both portable appliances and fixed installations should be checked.
• Hot work should be controlled with a permit-to-work system unless it is being carried out in a purpose-built area, such as a welding bay in a
• Smoking should be controlled in the

It is illegal to smoke in indoor workplaces in some countries. Even when it is not illegal, smoking can be controlled by company policies that ban or restrict it. In all cases, attention must be given to the safe disposal of smoking materials.

• Cooking and heating appliances should be used carefully and their use closely supervised. In particular, they should not be left
• Mechanical heat (such as friction from machinery and bearings) can be controlled by routine
• Deliberate ignition can be controlled by making good security arrangements for the A perimeter fence, security staff at entrances, CCTV, security lighting, etc. can help.

Systems of Work

Systems of work must be designed to minimise fire risk. The degree to which this is done and the exact procedures implemented should be decided through the risk assessment  process.

An example of a safe system of work applied to fire safety is the use of a permit-to-work system to control hot work (where naked flames, or a significant ignition source will be created).

TOPIC FOCUS

Typical precautions for control of hot work:

• Combustible and flammable materials are removed from the work
• Items that cannot be removed are covered with fire-retardant
• The floor is swept
• Any wooden floor is damped
• A suitable fire extinguisher is at
• A “fire-watcher” is present in the area while the work is carried

The work area is visited routinely after the work has finished to check the area for smouldering

Good Housekeeping

Good housekeeping is fundamental to fire safety and is about keeping the workplace:

• Waste-free, by removing waste on a regular basis (e.g. emptying full litter bins) so that it does not build up and increase the fire risk as a potential fuel
• Tidy, so that combustible and flammable materials are returned to safe storage after use (e.g. solvents returned to the solvent store).
• Well-ordered, so that fuel and ignition sources are kept separate (e.g. ensuring fan heaters are not obstructed).

Pedestrian routes should also be kept clear (e.g. with no obstructions by the fire-escape door), so that they can be used in the event of a fire evacuation.

STORAGE OF FLAMMABLE LIQUIDS IN WORKROOMS AND OTHER LOCATIONS

Flammable liquids have a relatively low flash-point (between 21°C and 55°C) and can be quite easily ignited with a heat source (such as a match) at room temperature.

Highly flammable liquids have a lower flash-point (from around 0°C to 21°C) and are therefore easier to ignite.

Extremely flammable liquids have an even lower flash- point (well below 0°C) and are very easy to ignite at room temperature. Petrol (gasoline) is a common example of an extremely flammable liquid.

The lower the flash-point, the more dangerous the substance. It is therefore essential that flammable liquids are used and stored safely.

TOPIC FOCUS

Safe use of flammable liquids:

• Use the minimum volume of liquid
• Liquid should be in a properly labelled
• Ideally the container will be metal with a self- closing lid.
• Use a metal tray to catch spills and have absorbent material
• Use the liquid away from heat and ignition sources.
• Ensure that the workspace is well
• Return containers to safe storage after use. Safe storage of flammable liquids in workrooms:
• Store minimal volumes
• Store in a purpose-built flammables cabinet, which should:
  • Be fire-resistant (usually metal).
  • Have lockable doors and fire-resistant hinges and
  • Be clearly
  • Have a built-in catch tray to contain
  • Be located away from ignition

Safe storage of flammable liquids in other locations:

• Store liquids in a purpose-built, single-storey flammables store, which should:
  • Be built of non-combustible
  • Have a lightweight roof for explosion
  • Ideally be built outdoors, away from other buildings, or with firewall
  • Suitably fenced in a secure
  • Be well ventilated at high and low
  • Have lockable access doors with sills to contain
  • Have clear and safe access for the fire
• All electrical systems should be intrinsically
• All other ignition sources should be
• Adequate fire-fighting equipment and suitable fire-safety signs should be
• Regular checks for security, secure and safe storage, leaks of liquids, etc should be carried

STRUCTURAL MEASURES FOR PREVENTING THE SPREAD OF FIRE AND SMOKE

Example Scenario

If a fire starts on the ground floor of a large, open-plan multi-storey building that has open stairwells, convection will drive the hot smoke from the fire upwards. The smoke will fill the ground floor of the building and then rise up each of the open stairwells. Each stairwell will, in effect, become a chimney. The hot smoke will then fill the upper storeys of the building. The fire will not be contained

and will spread through the building. The building will be destroyed, or suffer severe damage. Any people in the building, especially in the upper storeys, will become trapped and die as a result of fire and smoke inhalation

because they will not have time to escape, and their escape route (the stairwells) will be full of smoke and flames.

Compartmentation

The above scenario is obviously undesirable. If fire prevention does not work and a fire does start in a building, it should be contained and prevented from spreading. This can be done by designing the

building in such a way that it is divided up into separate compartments, each surrounded by fire-resistant materials that can resist the spread of smoke and flame.

This compartmentation is done at the initial design and build stage but may also have to be done if a building is changed or modified. This is normally a heavily legislated issue, which is subject to strict control and local standards.

If the multi-storey building in our scenario is compartmentalised, when the fire starts on the ground floor it will be contained in one part of the building. This will give time for the fire to be detected, the alarm raised and the building evacuated. Containment may result

in the fire dying down or even going out as a result of oxygen starvation. If this does not happen, then the fire will eventually break through the containment, but this will take time.

Constructing walls, floors and ceilings from fire-resistant materials and ensuring that the building is broken up into appropriate compartments is only fully effective if any openings in the compartment walls are sealed. Since people have to move through buildings, doors must be

fitted to openings. These doors must be built to withstand the spread of smoke and flames. Such doors are known as fire doors.

Typical characteristics of a fire door are:

• Rated to withstand fire for a minimum period of time (e.g. 30 minutes).
• Fitted with a self-closing
• Fitted with an intumescent
• Fitted with a cold smoke
• Vision panel of fire-resistant
• Clearly labelled (e.g. Fire Door – Keep Shut)

GLOSSARY

INTUMESCENT STRIP

A strip built into the edge of a fire door that expands when it gets hot, sealing the gap between the door and the door frame.

COLD SMOKE SEAL

A plastic or foam strip that seals the gap between the door and frame at all times.

Note that these are typical characteristics of fire doors and the actual specification will vary according to need and local standards.

Heavier fire doors may be needed to:

• contain fire within compartments that contain greater fire risk (e.g. a plant room); or
• keep fire out of compartments that contain fire- sensitive contents (e.g. a computer room), in which case a higher rating will be required (one hour, two hours, ).

Most fire doors are fitted with a self-closing device that pulls the door shut once a person has walked through it. Some fire doors are fitted with electromagnetic openers that keep the fire door open at all times. If the fire alarm activates, or the electrical supply to the opener is interrupted, the door is released and closes. This type of

door is common in corridors with heavy pedestrian traffic, where a normal fire door would be an obstruction

Properties of Common Building Materials

Fire affects different building materials in different ways. The use of building materials, therefore, has to be tightly controlled to ensure that appropriate materials are used in a structure. For example, fire compartments must be robust enough to withstand the spread of fire for their design time, and structural elements in a building should

not fail quickly when they are heated in a fire. There will be local regulation and standards to ensure fire safety.

• Concrete is usually very resistant to fire and does not collapse catastrophically. It may “spall” (throw off small chunks).
• Steel is severely affected by high temperatures. Expansion may occur, pushing structural elements apart. Steel may also twist and These effects can lead to catastrophic building collapse.

To overcome the problems associated with using steel as a structural material, it is usually encased in concrete or coated with a fire-retardant foam or paint (intumescent paint), which insulates it from excessive heat.

• Brick is usually very resistant to fire (bricks are made by exposure to very high temperatures in a kiln).
• Timber – thin timber, such as floor boards, will burn, but thick timber, such as structural beams, will not usually burn in a building fire (a layer on the outside of the timber will char and protect the inner core). Thick timber is unlikely to fail suddenly, but will do so

Other materials can also make a difference to fire resistance and the behaviour of a fire in a building:

• Insulation (such as wall insulation) can be combustible so fire-retardant versions must be
• Wall coverings (such as paint and wallpaper) can make a difference to the way fire spreads across surfaces, so they should also be closely

Protection of Openings and Voids

We have already noted that fire doors are used to ensure that door openings are protected in the event of fire.

However, buildings, and the fire compartments that they are made up of, will inevitably have numerous voids and openings running through them, such as:

• Lift
• Service
• Air-handling
• Voids between
• Roof voids,

All of these need to be protected to ensure that smoke and flame cannot easily travel from one compartment to another. This protection can be done in many different ways, e.g. a self-closing shutter held open by a fusible link (a piece of soft metal that melts at a very low temperature, releasing the shutter).

It is important that any new openings made in fire break walls are reinstated or protected in some way, e.g. when cables are run through a hole in a wall the hole might be filled with fire-retardant foam.

ELECTRICAL EQUIPMENT FOR USE IN FLAMMABLE ATMOSPHERES

Electrical equipment sited in an atmosphere containing a mixture of a dangerous substance and air could well ignite that explosive atmosphere if it is not built to the correct specification. For example, in the UK a standard 230 V inspection lamp taken into a storage tank containing petrol vapour would act as the ignition source for that petrol vapour. Dusts and vapours can result in flammable or explosive atmospheres.

Legislation, such as the European ATEX directives, will govern the control of flammable atmospheres and the use of electrical equipment in those areas. There are two of these directives: the ATEX 95 Equipment Directive, which controls equipment available for supply for use in flammable areas; and the ATEX 137 Workplace Directive, which requires the workplace to be controlled to ensure safety of workers. ATEX takes its name from the French title of the directive: Appareils destinés à être utilisés en ATmosphères EXplosibles (Devices for Use in Explosive Atmospheres).

Broadly, the ATEX Workplace Directive requires the employer to classify hazardous locations into zones and then control the fire and explosion risks as appropriate, where:

• an explosive atmosphere might be created by the presence of a dangerous substance in a gas, vapour or mist form mixed with air; or
• an explosive atmosphere might be created by the presence of a combustible dust mixed with

The zones are classified on the following basis:

For gases, vapours and mists the zone classifications are:

• Zone 0 – a place in which an explosive atmosphere is present continuously, or for long periods, or
• Zone 1 – a place in which an explosive atmosphere is likely to occur in normal operation
• Zone 2 – a place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period

  For dusts the zone classifications are:

  • Zone 20 – a place in which an explosive atmosphere is present continuously, or for long periods, or
  • Zone 21 – a place in which an explosive atmosphere is likely to occur in normal operation
  • Zone 22 – a place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short

  The employer would then be required to select the appropriate work equipment for use in the area. The ATEX Equipment Directive sets standards for the specification of electrical equipment that is intended for use in classified hazardous areas, as follows:

  Electrical Equipment	Zone
  Category 1	Zone 0 or Zone 20
  Category 2	Zone 1 or Zone 21
  Category 3	Zone 2 or Zone 22

  Note that Category 1 equipment can be used in Zones

  1 and 2 as well, and Category 2 equipment can be used in Zone 2. Such electrical equipment will be marked with an Ex sign in a hexagon, with a number indicating the category