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Spent limestone samples from the bed and baghouse of a 22 MWe circulating fluidized bed (CFB) boiler were hydrated and then sulphated in a thermogravimetric analyzer under conditions similar to those found in CFB combustors (850°C, 0.3% SO2, 9% O2, 9% CO2 and 81.7% N2). Hydration using water gave faster rates and higher levels of conversion of the residual CaO to Ca (OH)2 than immersion in pure steam at 150 and 200°C. The particles expanded during hydration and their internal volume increased from 0.1 cm3/g Ca before hydration to nearly 0.6 cm3/g Ca after dehydration. Hydration rejuvenated the reactivity of the bed material but not that of the baghouse particles. The conversion of Ca to CaSO4, in the treated bed particles increased from 32% to over 80% during re‐sulphation.

A method is presented for the prediction of the depth of lethal heat penetration into mineral soils beneath a spreading fire. The information required for this prediction is the total amount of heat transferred to the soil by the fire, the time the fire heats the soil, the physical properties of the soil, and the Newtonian cooling coefficient at the soil surface. The depth of lethal heat penetration can be determined from a diagram using dimensionless parameters. The predicted values are compared with measured values from a number of test fires conducted in our laboratory.

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