Ignition energy gases

The minimum ignition energy of Hquid acetylene under its vapor, when subjected to electrostatic sparks, has been found to depend on the temperature as indicated in Table 3 (86). Ignition appears to start in gas bubbles within the Hquid. 

From a safety standpoint, priority must be given to the measures in item 1. Group 2 cannot be used as a sole protective measure for flammable gas or solvent vapors in industrial practice with sufficient reliability, but can be applied as the sole protective measure when only combustible dusts are present if the minimum ignition energy of the dusts is high (>10 mj) and the operating areas concerned can easily be monitored. 

The ignition source energy must be above the minimum ignition energy (MIL) of the gas or vapor... 

Gas Mixture Minimum Ignition Energy for a Deflagration (mJ) Minimum Initiation Energy for a Detonation (mJ)... 

Flammable gas or vapor-air mixtures Due to their low minimum ignition energies (<1 mj), avoidance of effective ignition sources in flammable gas or vapor-air mixtures is in principle possible only in exceptional cases. For hot surfaces a maximum permissible surface temperature Tmax must be specified, with the help of the minimum ignition temperature (MIT) of flammable gases, vapors, or liquids, so that the temperature of all surfaces is not exceeded (Table 23-8). 

Hydrogen is produced or used in gas or liquid form in a number of processes. Hydrogen is a colorless, odorless gas that is easily ignited over a wide flammable range. Hydrogen burns very rapidly and cleanly in air with a nearly invisible clear blue flame. It has flammable limits of 4-74% in air and minimum ignition energy of 0.02 mj, compared to 0.25 mj for typical hydrocarbons. 

When heat is supplied to a gaseous mixture of oxidizer and fuel components, i. e., a premixed gas, an exothermic reaction occurs and the temperature increases. The reaction may conhnue and proceed into the unreacted portion of the mixture even after the source of the heat is removed. The amount of heat that has to be supplied to the mixture to achieve this is defined as the ignition energy. If, however, the reac-hon terminates after removal of the heat source, ignition of the mixture has failed. This is because the heat generated in the combustion zone is not sufficient to heat the unreacted portion of the mixture from the initial temperature to the ignihon temperature. 

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