Second item ignition

For remote ignition under autoignition conditions, direct flame heating is small or zero, so the critical compartment temperature needs to be greater than or equal to the autoignition temperature, e.g. about 400-600 °C for common solid fuels. 

For ignition by flame contact (to a wall or ceiling), the flame heat flux will increase with Dp, the flame thickness of the igniter, estimated by 

The exposed area of the second item exposed (AF ) depends on the flame length (zf) and its diameter. 

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Gas Temperature Approximate Scale (°C) Figure 11.21 Second item ignited... 

For the second item ignition to lead to flashover, the area involved must equal or exceed the total critical area needed for the second item. The time for ignition depends inversely on the exposure heat flux (Equation (11.51)). Figure 11.21 shows the behavior for ignition of the second item, where Af,i is the fixed area of the first item and AF c is the critical area needed. The energy release rate of both fuels controls the size of the jump at criticality and depends directly on AFAhc/L. No flashover will occur if the jump in energy for the second item is not sufficient to reach the critical area of fuel, AFjc- The time to achieve the jump or to attain flashover is directly related to the fuel property,... 

Ignition of a second item, representing an initial fire (e.g. chair, liquid spill) and the prospect of ignition of an adjoining item. 

In the new method of multiple designation used here, the first "2 referred to the gas and fuel reservoirs, the second "2" to the flame gun. (2) CWTC Item 935, Standardization of Flame Thrower, Portable, M2-2, Kit, Service, for Portable Flame Thrower, M2-2, and Cylinder, Ignition, Portable Flame Thrower, 17 Mar 44. 

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