C2 PRINCIPLES OF FIRE & EXPLOSION Flashcards
Explain the meaning of the term safe isolation
Safe Isolation
The interruption, disconnection and separation of all the equipment’s motive power sources in such a way that this disconnection and separation is secure by lockable means.
Identify four ignition sources that could arise from maintenance or operations on an installation
Ignition sources are (select four)
• Electrical equipment
Routinely inspect and test to prevent faults developing that could cause sparks and overheating.
• Hot work
Welding, burning, etc. - control with a permit-to-work when done in sensitive areas.
• Smoking
Control and limit to restricted areas on site (welfare areas).
• Cooking and heating appliances
Locate safely, confine to a galley offshore and use carefully.
• Mechanical heat (overheating)
Control by good maintenance programmes.
• Deliberate ignition
Prevent by good security, perimeter fences (onshore), CCTV and security lighting.
What are the three elements that make up the fire triangle
Oxygen
Heat - (Ignition)
Fuel
What are the five stages of combustion
The five stages of combustion are:
Induction
Heat is initially supplied by an external source which results in production of flammable vapour.
These vapours mix with air above the fuel and, if sufficient energy is provided, the combustion reaction begins between the vapour and the oxygen.
Ignition
The point of ignition is reached when the reaction becomes self-sustaining (and no longer requires an external heat source).
At this stage combustion develops very quickly and there is a dramatic increase in temperature as the fire grows.
Growth
Once ignited, the fire may spread through direct burning or through the typical mechanisms of heat transmission (convection, conduction or radiation).
The rate, scale and pattern growth depend on a number of factors such as:
The nature, form and amount of oxygen (open, ventilated versus sealed containment); the amount of heat produced by the reaction.
Steady State
After the growth period the temperature stabilises and the combustion process reaches a steady state where the reaction between fuel and oxygen is balanced until all the fuel is consumed.
Decay
Decay will begin when either the fuel or oxygen has been consumed.
The fire will extinguish and gradually cool down.
In the early stages of decay, there is still a considerable amount of heat; there is certainly enough to cause re-ignition if more fuel or oxygen is supplied.
In the latter case, admission of oxygen (e.g. opening a window) into an oxygen-depleted room can result in a sudden explosive re-ignition of vapours.
