Abstract: A heated chamber having at least one opening; closure means for closing said at least one opening, said closure means having at least a closed and open position; said closure means and said opening having surfaces disposed for coming into proximity of one another in said closed position, said surfaces forming a primary sealing means for said heated chamber in said closed position, there being a substance applied to at least one of said proximate surfaces, said substance having a property of expanding upon the application of heat thereby forming a secondary sealing means between said proximate surfaces in said closed position.