PURPOSE: To prepare a pyrogenic compsn. which is easy to handle without heat loss, by filling metallic iron and a homogeneous mixture of components other than the metallic iron separately in air-permeable packages and encasing the packs in an airtight packaging material.

CONSTITUTION: Predetermined amounts of (A) a mixture prepared by scattering or spraying an aqueous NaCl solution which may contain a filler when necessary, over a blend of activated carbon and a filler, followed by further mixing and (B) metallic iron are filled separately in air-permeable packages and the packs are put in an airtight packaging material. No equipment nor operation for N2 gas purging, etc. are required, for the homogeneous mixture of components other than the metallic iron does not develop heat even in contact with air. For use, (A) and (B) are filled in an air-permeable packaging material for mixing and generation of heat.