Unit C1 2.1 Fire and combustion

Question 1

What is a flash point

Answer 1

The lowest temperature of a liquid at which sufficient Vapour is given off to ignite (momentarily, flash) when an external source of ignition is applied. Sustained combustion does not occur.

Question 2

Name four sources of fuel

Answer 2

Combustible solids
e.g. wood, plastics, paper and wrapping and packaging materials, soft furnishings, and some metals.

Flammable solids, e.g. magnesium, in finely divided form e.g. powder.

Flammable liquids e.g. petrol, paints, solvents and oils/fats.

Flammable gasses e.g. hydrogen, LPG, methane.

Question 3

Name eleven ignition sources

Answer 3

Open flames (matches, welding torches)
Electrical sparking sources.
Spontaneous ignition.
Sparks from grinding or tools.
Static electricity.
Friction.
Hot surfaces (heaters or overheating surfaces)
Sparks ( from grinding, electrical arcing, or static discharges.
Lasers and other sources of high energy radiation.
Chemical reactions giving rise to heat/flame.
Smoking.

Question 4

Define fire

Answer 4

A combustion reaction in which fuel is converted into combustion products (smoke, fumes or gases) in the presence of oxygen. It is a rapid self sustaining gas-phase oxidation process which produces light and heat.

Question 5

How does combustion take place in solids and liquids?

Answer 5

The vapours given off rather than the solid or liquid ignite,therefore the combustion reaction takes place at, or above the surface of the solid or liquid.

Question 6

What are the five stages of combustion?

Answer 6

Induction. A heat source heats the fuel enough to produce flammable vapours which mix with the air above.
Ignition. The point of ignition is reached when vapours are hot enough to combust (react with O2 to produce combustion products) the reaction becomes self sustaining.
Growth. Combustion develops very quickly and temp. rises rapidly. Fire spreads by convection, conduction or radiation. RATE-SCALE-PATTERN of growth depend upon:[Nature, form and amount of fuel][Availability of O2, open,ventilated vs sealed containment]
Steady state. After growth the tempstabilises and the combustion is balanced (reaction between fuel and O2) Fire can still be spreading but rate of burning and temp. are not increasing.
Decay. Begins when O2 or fuel is depleted. Fire will eventually extinguish and cool. Early stages of decay still have enough heat to reignite if fuel or O2 is introduced.