Why moderate magazine heat can damage charge bags

How can temperatures only moderately above room temperature harm a ship's magazines?

Heat can compromise materials that hold charges together, allowing bags to open and powder to spill even without an immediate ignition.

Some charge-bag materials and seals are intended to remain solid during storage and disappear rapidly when the gun fires. Heat above their intended storage conditions can therefore damage them even before a charge ignites. An unnamed Royal Navy battleship is recalled as suffering bag closures that failed and released loose powder into its magazine, prompting added insulation. Expectations that surrounding seawater and the metal hull would dissipate heat did not always match the way heat spread within the ship.