A fire extinguishing device of the explosive type is disclosed for use in interior or localized exterior conflagrations, wherein the force of detonation of the device is minimalized through the use of low density/low mass components; no part of the device having sufficient mass or density to typically constitute a safety hazard as flying debris, nor be dangerous in concussive shock due the explosive burst. The present invention is composed of a lightweight casing of rigid plastic foam or other suitably frangible material, with an abrasion-resistant, thin plastic, protective, exterior sheathing. Within the internal cavity of the device, a low explosive yield detonator is located at or near the center of mass, and is actuated by fuse cord(s) extending from the detonator, the end(s) of which extend(s) from the interior detonator to a mounting at or near the exterior surface. The interior volume of the hollow casing is chargeable, through variations in internal configuration, with a variety of fire-retardant chemical agents, including dry powders, two-part reactants, liquid components or others, singly or in combination.