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CLASS 3 - FLAMMABLE LIQUIDS

NDGTC. CLASS 3 - FLAMMABLE LIQUIDS. This class makes up more than 50% of all the dangerous substances moved by road in the UK each year Flammable liquids can be divided broadly into two categories:

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CLASS 3 - FLAMMABLE LIQUIDS

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  1. NDGTC CLASS 3 - FLAMMABLE LIQUIDS This class makes up more than 50% of all the dangerous substances moved by road in the UK each year Flammable liquids can be divided broadly into two categories: • Liquid fuels, mostly (but not all) petroleum derived, e.g. petrol, kerosene, diesel, gas oil • Solvent and raw material applications, e.g. methanol, ethanol, acetone, toluene

  2. NDGTC FLAMMABILITY • It’s not the liquid, but its vapour that burns • Evaporation causes great increase in volume - from two to four hundred-fold • Volatility - the readiness with which a liquid evaporates • Higher volatility means greater fire hazard • Evaporation can only happen on exposure to the atmosphere • So effective containment prevents vapour formation and so prevents fires

  3. NDGTC PRECAUTIONS TO AVOID SPILLAGE Tankers/tank containers • Ensure all hose connections are properly and securely made • Securely close all valves, manlids, etc. after loading/unloading • Ensure tank/compartments are not overfilled • Drain hoses and ensure end-caps fitted • Strictly observe all site procedures Packaged goods • Refuse leaking or badly damaged receptacles • Check that all receptacles are safely loaded and securely stowed • Report any leaks (however small) that develop during the journey

  4. NDGTC SEGREGATION Flammable Liquid + Oxidiser = Potential explosion Thus it is vital that these two danger labels are kept well apart during handling and transport

  5. NDGTC OTHER HAZARDS • Some flammable liquids are also toxic and/or corrosive • Some flammables produce acidic or toxic gases when they burn • Some toxic flammables are also skin absorptive • Skin contact can give rise to allergies & dermatitis • Vapours can cause strong eye irritation • Inhalation of certain vapours can lead to poisoning, narcosis, or damage to lungs, brain tissue, etc. See ‘Tremcard’ for details

  6. NDGTC OTHER FLAMMABLE VAPOUR DANGERS Since flammable vapours are heavier (denser) than air, accumulations in confined spaces can lead to suffocation danger Flammable vapours are all colourless, so leaks will not be normally be visible Most have a perceptible smell, so this could warn of leaks Because of their density, vapours can flow some distance from the leak, particularly where confined or channelled by drains, ditches, etc. and cause a fire hazard elsewhere

  7. NDGTC FLASH POINT • The ease with which a flammable liquid catches fire is referred to as its flammability • The commonest measure of flammability is the flash point • Defined as the lowest temperature of a liquid at which it gives off just sufficient vapour to form an ignitable mixture with air • Thus, the vapour from a liquid below its flashpoint is insufficient to ignite • The vapour from a liquid at or above its flashpoint can be ignited • Low flashpoint indicates high flammability • The flashpoint is the chief determinant of whether or not a flammable liquid is regulated • Under CDG, ADR & IMDG, liquids with flashpoint 60 C. or less are in class 3 • (Diesel extended to 100 C)

  8. NDGTC AUTO IGNITION TEMPERATURE • Even with a vapour-air mixture in the right proportions, an adequate temperature will be needed to ignite it • This could be an external ignition source, or the mixture could self-ignite if it became hot enough • This temperature is called the auto-ignition temperature • Some examples: • Acetone 540 deg.C • Petrol 300 deg.C • Diesel 250 deg.C • Carbon disulphide 100 deg.C • Note the particularly low value of carbon disulphide which could even be ignited by contact with hot water pipes, vehicle exhausts, etc.

  9. NDGTC FLAMMABLE RANGE • Flammability depends not only on vapour and air mixing, but also on how much of each is present • A flammable atmosphere is a vapour-air mixture within the correct proportions to burn • The top end of the range is called the upper explosive limit (UEL) and the bottom the lower explosive limit (LEL) • Outside these limits, the mixture will not burn • Some examples: • Petrol 1% ---- 6% • Acetone 3% ---- 13% • Methanol 7% ---- 37% • Thus, an explosive mixture could build up in a notionally empty tank or receptacle where air and residual vapour have mixed

  10. NDGTC VOLUME RATIOS Remember that when a liquid evaporates there is always a huge increase in volume, for petrol roughly 250 times. So this 40,000 litre petrol tank is capable of producing 40,000 x 250 litres of petrol vapour (i.e. 10 million litres) which when mixed with air at the lower end of the flammability range, say 2% gives about 500,000,000 litres of highly flammable atmosphere

  11. NDGTC MISCIBILITY • Tremcards will describe flammable liquids as being miscible or immiscible with water • Meaning will, or will not mix with water e.g. Miscible - methanol, acetone Immiscible - petrol, benzene • This is important to the emergency services when dealing with a fire • Water will not deal with an immiscible liquid fire and may well make it worse by spreading it • Water will deal with a miscible liquid fire, but large quantities may be needed, and jets should be avoided

  12. NDGTC FIRE AND FLAMMABLE LIQUIDS Remembering the fire triangle, when vapour and air are present in the right proportions, all that is necessary is a source of ignition. Examples to be avoided: • Smoking, matches, lighters, portable stoves • Static electricity - make sure of earthing • Lightning - loading/unloading should cease • Current sparks - mobile phones, CBs • Vehicle defects - hot tyres, bearings, brakes • Vehicle accidents - drive carefully The oxygen side of the fire triangle is always present, so vapours must be contained and sources of ignition must be kept away

  13. NDGTC PERSONAL PROTECTIVE EQUIPMENT • Goggles and gloves should be regarded as the absolute minimum • Respirators may be needed where vapours pose a breathing danger • Tanker drivers tend to need higher levels of protection because of their greater potential exposure • Always read the Tremcard (or similar) and as a final note - Some substances with flashpoints higher than 60C. may be carried as class 3 if transported at temperatures above their flashpoint e.g. Liquid tar at 150 deg.C

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