Patent ID: 8269155

Claim:
A heat retaining device comprising: (a) an enclosure member having a preselected shape, including a top portion and bottom portion attached to each other to form a sealed chamber; (b) a heat retention material within said sealed chamber, said heat retention material being capable of being heated by thermal energy radiation and of retaining heat in a latent state for at least a preselected time; (c) an aperture in at least one of the top or bottom portions of said enclosure member; and (d) a pressure relief mechanism disposed in the aperture that seals the aperture from the ambient environment external to the sealed chamber when the enclosure member is in a normal condition, wherein at least one of the top and bottom portions of said enclosure member are deformable when the heat retention material has been abnormally and excessively heated by thermal energy radiation so as to cause excessive pressure to deform at least one of said portions of said enclosure member, said deformation causing the pressure relief mechanism to open a fluid communication path through said aperture, thereby to permit excess pressure built up within the enclosure member to be relieved to the ambient environment through said pressure relief mechanism; and wherein at least one of said deformed portions of said enclosure member returns to its normal condition when the pressure is reduced.