Secondary ignition

In order for a fire to propagate from the product first ignited to another one, two conditions are necessary. Firstly, sufficient heat needs to be released to cause secondary ignition. Secondly, the heat release needs to occur sufficiently fast so that the heat is not quenched in the cooler air surrounding the latter product. 

The rule should be to keep the more hazardous mixts at minimum size. Transfer lines (such as fuses, quickmatch, etc) between prime ignition and first fire are regarded as a part of the secondary ignition system... 

In view of the above, it is clear that if the combustion of airflow is being adjusted on the basis of the oxygen content of the stack or convective section gases (i.e., from readings taken on an oxygen analyzer with probe located in the stack or convective section), it is very likely that there will be afterburn or secondary ignition in the stack or convective section. This scenario was discussed earlier in this chapter in the section on secondary combustion and afterburn. After all, the fire is supposed to be contained within the firebox, and not in the convec-... 

Transfer lines between prime ignition and first fire must be regarded as a part of the secondary ignition system. Quickmatch, a type of black powder fuse that has a more-or-less well-defined burning time and thus acts as a delaying element, will be described in the next chapter. It becomes a nearly-instantaneous transfer line if enclosed in a narrow paper tube and is thus used as piped match in fireworks for simultaneous initiation of several effects. ... 

Some thermoplastics (such as polyolefins, polyamides) form hot melts when burning, which can be quite dangerous as flaming drops fall onto combustible materials as secondary igniting sources. It may thus contribute to fire spreading and may be hazardous to the escaping public or to the firemen. 

Product flame retarded by brominated additives Total lives saved from direct ignition Total lives saved from secondary ignition Total lives saved Maximum potential lives saved... 

Fires involving gases or liquefied gases, e g. methane, propane and natural gas. Both foam and dry chemicals can be used on small fires, backed up by water to cool leaking containers. To control a fire from a major gas leak m require isolating the fuel supply. Direct flame extinguishment is difficult and may be counter-productive. If the leak continues there may be a secondary ignition. 

But if the fins have just become brittle enough to break off by hand, the problem is afterburn. The fins have simply been burned up by secondary ignition. While oxidation is a form of corrosion, we have discussed this problem in our chapter concerning the flue-gas side of fired heaters. (See Chap. 29.)... 

Secondary ignition Re-ignition of the flue gas in the convective section of a heater. 

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