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Explosive limits indicate the amount of gas needed for a mixture to be flammable. They have upper and lower limits and vary with temperature and pressure. Understanding these limits is important for ventilation and safety in environments with potentially combustible gases.
An explosive limit is a measurement that indicates how much of a particular gas must be present in the air for that mixture to be flammable or combustible. This measurement is typically given as a percentage and is usually accompanied by a temperature and pressure gauge where this measurement is accurate. Both temperature and pressure can alter this number, so standardization is important when comparing the limits of various chemicals. An explosive limit is often given in two different forms: the lower explosive or flammable limit which indicates the minimum amount required for combustion and the upper explosive or flammable limit which indicates the maximum amount that can be present for a mixture to be flammable .
Also called a flammability limit, an explosive limit typically indicates how much of a particular gas or chemical must be present in the air for that mixture to be flammable. Different gases have different explosive limits and an understanding of these various limits is important for proper ventilation in any environment where such gases are used. The explosive limit for a gas is indicated either as two different values, the upper and lower limits, or as an expression of the range between these two limits.
A lower explosive limit for a gas is the percentage of a gas that must be present for it to become combustible. Any amount of gas below this percentage is considered “too lean” to become combustible. This is important for the storage of potentially combustible gases and most regulations require adequate ventilation to ensure no more than 25% of this lower explosive limit.
The upper explosive limit for a gas is the highest amount of that gas that can be present for the gas to remain combustible. If this limit is exceeded, the mixture is defined as “too rich” and no longer burns properly. This value is important for mechanical engineering and other work using fuel gases, to ensure that mixtures react correctly for various uses.
An explosive limit for a gas will typically depend on the pressure and temperature in which that gas is contained. Higher temperatures reduce the lower limit and raise the upper limit, creating a wider range in which gases are explosive. Higher pressures, however, increase both values, but flammable gases contained at higher pressures can cause explosive combustion if ignited. This is why the explosive limit for a gas will usually be stated with the temperature and pressure for that given limit, to allow for a correct comparison of different gases.
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