Module 3 Learning Outcome

What components do you think are needed for a fire to begin?

Fire is a chemical reaction that gives off light and heat. Fire occurs when oxygen, heat and a fuel source come together to for the ‘fire triangle’. If any of these components are absent a fire cannot occur.

By knowing the various sources of each of these components, you may be able to prevent a fire happening.

We will now look at some examples of where these three components can be found in the workplace, starting with oxygen.

Oxygen –

 sources of basic oxygen include:

  • Air – for example, this can be enhanced by wind or by natural or powered ventilation systems etc.
  • Oxygen cylinders
  • Chemicals- for example nitrates, peroxides etc. release oxygen when they burn.
Heat –

Sources of heat/ignition include:
  • Naked flames- for example smoking materials, cooking appliances, heating appliances etc.
  • Sparks- for example grinding materials, impact tools, electrical equipment etc.
  • Hot surfaces – for example lighting, hot bearing and drive belts etc.
  • Static electricity – for example from the separation of materials such as pouring highly flammable liquids, walking across insulated floors etc.

Finally, we’ll look at some sources of fuel that can be found in the workplace.

Sources of fuel include:
  • Solid fuel – for example wood, paper, plastics, rubber, foam, textiles etc.
  • Gas fuel – for example flammable gases like Liquid petroleum Gas(LPG), acetylene and hydrogen etc
  • Liquid fuel – for example paint, varnish, methylated, spirits, white spirits, paraffin, acetone and etc.

Sources of these components can be found all around the workplace.

If you can keep these three components apart, you can prevent a fire from occurring.

STAGES OF FIRE

Fires pass through four stages:

  • Ignition (Incipient)
  • Growth
  • Fully developed
  • Decay

The ignition stage is usually represented by a very small fire which often goes out on its own, before the next stages are reached.

Recognising a fire in this stage provides your best chance at suppression or escape.

Ignition:

A fire at this stage is much easier to deal with and can be extinguished by a competent person trained in the use of fire extinguishers.

Fires in the workplace can start due to many different reasons. Some of the most common causes of workplace fires are:

    • Electrical equipment
    • Deliberate ignition
    • Hot work (welding, grinding etc)
    • Smoking
    • Cooking appliances
    • Heating appliances
    • Unsafe use and storage of flammable liquids
Growth

The growth stage is the shortest of the four stages, this is where the fire moves from its point of origin and begins to involve other combustibles.

A fire at this stage is much more difficult to stop. If you come into contact with a growth stage fire you should raise the alarm and leave the vicinity.

Fully developed

When the growth stage has reached its maximum and all combustible materials have been ignited, a fire is said to be fully developed. This is the hottest phase of a fire and the most dangerous for anybody trapped inside.

Decay

The decay stage is usually the longest stage of fire. It is characterised by a significant decrease in oxygen or fuel, putting an end to the fire. Although the area should still not be entered until the emergency services have given the all clear.

The spread of Fire

Fire transmits heat in four ways. It is important to understand these in order to manage the risk fire presents.

Heat can be transmitted by:

  • Direct burning
  • Convection
  • Conduction
  • Radiation

Combustible materials catch fire due to direct contact with flames which causes fire to spread.

This is known as direct burning.

Hot air rises, if inside a building, the hot gases generated by a fire will continue to rise until they come into contact with ceiling. Here they will spread out to form a layer beneath the ceiling.

These hot gases may then come into contact with combustible materials, which if heated up sufficiently by the gases, will set alight.

This is known as convection.

Heat can be transmitted through a material with sufficient intensity to melt or destroy the material. The heat may also ignite combustible materials which come into contact with, or are close to the hot section.

This is known as conduction.

A fire will give off heat energy in the form of infrared heat waves that can pass through transparent surfaces such as glass. If heated sufficiently adjacent materials may ignite.

This is known as radiation.

Fire Extinguishers Newport FIRE CLASSIFICATION

Class A fires involve solid materials where there are normally glowing embers during combustion.

Class B fires involve liquids or liquefied solids: they can be subdivided into two

  • Class B1 – Fires with water soluble liquids
  • Class B2 – Fires with non-water-soluble liquids

Class C fires involve gases

Class D fires involve metals

Class F fires involve high temperatures cooking oils and fats

E – Electrical fires (does not constitute a class because it will not feed a fire if switched off or isolated) – fires involving electrical equipment.