Class 3 - Flammable Liquids

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Flammable liquids evaporate to create flammable vapours - these burn, not the liquid.  Flammable and inflammable have the same meaning.  Non-flammable means it will not burn.  Miscible means a product will mix – such as ethanol with water.  Immiscible means it will not mix, such as petrol with water.  Flammable liquids are volatile. Danger increases with volatility as the flammable liquid more readily evaporates.  Flammable liquids tend to have a low viscosity, as they flow quickly.  Oil is viscous, petrol is not but it is very volatile. making petrol more dangerous.

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When a flammable liquid evaporates, it releases vapours that are invisible and heavier than air.  The vapours flow down and away from the flammable liquid, and collect in low laying areas.  This presents a fire risk, and those areas may not have oxygen to breathe.

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The flash point is the temperature at which the liquid generates enough vapour to flash but then go out.  Above the flash point, the flammable liquid continues to burn.  Below the flash point, no burning occurs as there isn’t enough flammable vapour.  Any flammable liquid with a flash point of 60C or lower is subject to ADR regulations.  Diesel is an exception to this, having a flash point of 65C.  Flammable liquids with a higher flash point than 60C that are loaded or unloaded at temperatures above their flash point are also subject to ADR regulations.

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The packing group of flammable liquids depends on their flash points and initial boiling points.  If the flammable liquid is heated sufficiently, it will reach its autoignition temperature, will ignite and burn without a source of ignition.  The autoignition temperature is always higher than the flash point.  Different flammable liquids have different flash points and autoignition temperatures.

 

Flammable liquids generate vapours that burn, but will only do so in the correct ratio with air, very similar to that of class 2.1.  Petrol, is flammable from 1 to 7% concentration in air, so it will only burn between those concentrations.  Methanol has a flammability range between 7 and 37%.

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Flammable liquids are also subject to a bleve if heated when in a sealed container, like class 2.1.  Flammable liquid vapours are ignited by sparks, so earthing is required during product movement.  Antistatic clothing may also be required. 

Flammable liquids cause damage to eyes and dermatitis to skin.  These must be washed with water if contaminated.

Class 3 may have subsidiary hazards too – it may be toxic (class 6.1) and / or corrosive (class 8).  The minimum PPE required is a high visibility vest, goggles and gloves.  A respirator is required if the flammable liquid is also toxic.

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