This is the temperature at which the fuel will continue to burn after ignition for at least 5 seconds when a small flame is brought near it. Generally, the fire point is 5-40°C higher than the flash point. Ignition point (kindling point) The kindling point is the lowest temperature, where a substance will auto-ignite and combust in normal atmospheric conditions, without any external influences. Kindling points can change depending on altitude, and the partial pressure of oxygen present. Auto ignition temperature This is the minimum temperature at which the vapour or air mixture over a substance spontaneously catches fire, that is, the vapour mix ignites without the need for a flame or a spark, the process of spontaneous combustion. Spontaneous combustion can begin without any flame, spark, heat, or other ignition source. Substances like boranes, silanes, and white phosphorous all have notoriously low auto-ignition temperatures. Gasoline has a relatively high auto-ignition temperature. A quite common everyday occurrence of this type of combustion, happens with paint or cleaning solvents, when saturated cleaning cloths are not correctly disposed of, and are placed along with combustible materials in 'regular' waste bins, and subsequently, the vapours from the saturated cloths spontaneously ignite. Consider how such contaminated cloths or similar materials should be disposed of. It would be useful to refer to the fire triangle and fire tetrahedron, described at the beginning of this element. Vapour density This is defined as the ratio of the density of the gas or vapour to the density of air (vapour density of air=1). Generally, vapours from flammable liquids are denser than air and thus tend to sink to ground level. Such vapours can travel some distance, and encounter ignition sources remote from the initial point at which the vapour first started. An example of a control measure when working with heavier than air vapours, is a fume cabinet found in laboratories. The cabinet is a semi-contained area with specialised extraction which ventilates the fumes directly away (specialised extraction, also local exhaust ventilation or LEV ) . Vapour pressure Vapour pressure is defined as, the partial pressure of a gas in equilibrium with a condensed form (solid or liquid) of the same substance and is a measure of a liquid's volatility. A high vapour pressure usually is an indication of a volatile liquid or one that readily vaporises. The boiling point This is the temperature at which the vapour pressure equals atmospheric pressure, such that the pressure of the atmosphere can no longer hold the liquid in a liquid state and bubbles begin to form. In general, a low boiling point indicates a high vapour pressure and possibly, an increased fire hazard. Flammable and highly flammable Materials of solid, liquid or gas can be stored and used in the workplace. They can be classed as flammable or highly flammable. Flammable material ignites easily and burns rapidly with a flame or
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