This Slimline anti arson letterbox is a sealed unit that holds the flammable material, including liquids, preventing the fire from spreading. The neoprene seal around the opening ensures that the PostSafe is airtight, this starves the fire of oxygen extinguishing it at this point in most cases. If the fire persists, the tubing automatically releases the extinguishant putting out the fire. The fire cannot be restarted as the liquid released prevents this from happing. With an external height and width of 500mm x 320mm and an internal depth of 90mm, this letterplate is powder coated and comes supplied with 2 keys.