Time-to-ignition

Spillage of a weak (5%) aqueous peroxide solution onto cotton waste led, after some time, to ignition. This probably involved concentration of the peroxide by evaporation/absorption of the water, the heat insulating effect of the fibrous mass preventing heat loss as oxidation proceeded, and possibly the presence of trace metals in the waste promoting catalytic decomposition. 

Rate of heat calorimeters can be used to measure a number of the most important fire hazard parameters, including the peak rate of heat release, the total heat release, the time to ignition and smoke factor (a smoke hazard measure combining the total smoke released and the peak RHR [14, 18-20]). The smoke factor will give an... 

Toxic potency of smoke data can be used as one of the inputs in fire hazard assessment. In particular, they can be combined with average mass loss rates and times to ignition to obtain a quick estimate of toxic fire hazard. 

It has already been shown that the Cone calorimeter smoke parameter correlates well with the obscuration in full-scale fires (Equation 1). At least four other correlations have also been found for Cone data (a) peak specific extinction area results parallel those of furniture calorimeter work [12] (b) specific extinction area of simple fuels burnt in the cone calorimeter correlates well with the value at a much larger scale, at similar fuel burning rates [15] (c)maximum rate of heat release values predicted from Cone data tie in well with corresponding full scale room furniture fire results [16] and (d) a function based on total heat release and time to ignition accurately predicts the relative rankings of wall lining materials in terms of times to flashover in a full room [22]. 

The ignition process for FRC materials can be described in terms of the relationship between time to ignition and heat flux. A technique developed by FMRC using its Small-Scale Flammability Apparatus (2-6) was used for the quantification. 

Ignition. For thermally thick materials, time to ignition is found to follow the following relationship as external heat flux is varied ( 4,6) ... 

Experimentally, time to ignition is measured at various heat flux values and critical heat flux for ignition and TRP are quantified using techniques such as the one used in the FMRC Small-Scale Flammability Apparatus ( 4,6). 

Explain how the time to ignition of a solid can he based on conduction theory. 

Calculate the time to ignite (piloted) for the materials listed below if the irradiance is 30 kW/ m2 and the initial temperature is 25 °C. The materials are thick and the convective heat transfer coefficient is 15 W/m2 K. Compute the critical flux for ignition as well. 

Hydrocarbon fires are a principal concern in many processing facilities. There are many different types of hydrocarbon fires. The mode of burning depends on characteristics of the material released, temperature and pressure of the released material, ambient conditions, and time to ignition. Types of hydrocarbon fires include ... 

The time to ignition can be expressed by equation (2.10) which is similar in form to the Arrhenius equation. 

Almost simultaneously the second fuse is lit by the top break explosion, the burning of this fuse being timed to ignite the gunpowder in the middle compartment just as the red stars are burning out. 

FIG. 5.8 "Henkin-McGill Plot" for nitrocellulose. The natural logarithm of the time to ignition is plotted versus the reciprocal of the absolute temperature (°K). A straight line is prociuced, and activation energies can be calculated from the slope of the line. The break in the plot near 2.1 may result from a change in the reaction mechanism at that temperature. Source reference 6. 

Under the heading "General Case , Ma ek states (p 47) that in order to solve eq (1) with out approximations subject to specific boundary conditions, one has to resort to numerical procedures. G. B. Cook (Refs 6a 7a) treated two problems by means of calcns with. digital computers. First is the case of a slab of solid expl,one face of which was in contact with. a constant-temp bath. In the 2nd case the expl was subjected to a time-dependent heat pulse. In both. cases the time to ignition and the critical condition for ignition are given as... 

C. Measurement of times to ignition of explosive exposed to hot flames. 

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