558 TRANSACTIONS OF THE 



1. When the water in the boiler has been allowed to fall be- 

 low the flues, the shell and steam drum or chimney, as the case 

 may be, become sufficiently heated by radiation from the super- 

 heated steam within, to effect ignition of wood work immediately 

 exposed to it. 



2. When water has been allowed to fall below the flues, as 

 just referred to, and the occurrence is disco verd, it is customary, 

 immediately to haul the fires from out of the furnaces into the 

 fire room, and when the wood work immediately over and 

 around the fire room is not properly protected, fire is likely to 

 communicate to it, and fires from this cause have frequently oc- 

 curred. 



3. When blowers are used, the fire or sparks that may be blown 

 out through fissures in the furnace doors, ash pits, flue holes, 

 chimney connexions, &c., will readily ignite wood already at a 

 high temperature and quite charred, from having been before ex- 

 posed to such temperature. 



Chimney Jackets and Rooms. — In single decked steamers, when 

 the boikr is below, and the steam chimney is above the main 

 deck, or when the boiler is on the main deck or upon the wheel 

 guards, it is customary in many cases, to cover the chimney or 

 chimneys, as the case may be, with a wooden casing, set off from 

 it but a few inches, and in others to cover it with a sheet iron 

 jacket, in most cases imperfectly made, and in all, insufficiently 

 fitted. In steam vessels with two or more decks, the boiler or 

 boilers being in the hold, the steam chimuey and the base of the 

 smoke pipe are commonly enclosed in wood work alone, which is 

 in some cases set at a proper distance from the chimney, to avoid 

 the risk of it being fired by sparks or the continued radiation of 

 heat from it, but tlie purpose of this space is very frequently 

 negatived, by its being used for the storage of swabs, buckets, 

 brooms, &c., &c. 



This wood work, however, is very seldom properly protected, 

 in many cases no protection at all is attempted; in some a coat of 

 whitewash is laid on, and in others a lining of tin, zinc, or iron, 

 in which the laps of the sheets are laid downwards, as if they 

 were there placed to shed rain or water falling from above, instead 

 of fire arising from below. The tin, and even the zinc, unless 

 well nailed, are too light, and their expansion at high tempera- 

 tures too great for this purpose : the consequence is, that when 

 subjected to the heat of the smoke pipe, they wrinkle and spring 

 to such a degree, as not only to admit any sparks that may arise 

 up from below, to pass between their laps and under them to the 



