Fire-proofing a door adds precious minutes to a barrier that stands between a person and flames on the other side. There are two major ways of fire-proofing. One way is through the application of a coat of resin or organic agent to the surface of the door. The other way is to soak the door in a solution until minerals have permeated the wood.
The first way is accomplished through the use of an organic agent known as an intumescent which inhibits burning. Historically there are have been other agents like endothermic resins but recently have fallen out of favor as they produce excess smoke that compounds the difficulty of seeing during a fire emergency.
Intumescents cannot hold off a fire from a door forever but merely retard flames and increase the time it takes for the door to ignite. They are applied as a thick coat in the manner of paint onto the surface of the door. Exposure to excess moisture and constant heat is discouraged to protect the efficacy of these agents.
The second way of fire proofing is to soak the entire door, as long as it is not yet painted and finished, into a solution. Commonly ammonium or zinc salts are used. After soaking and drying these woods become highly impervious to heat. However, the second method is much more labor intensive than the first.
A very new kind of door is the fiberglass door. Strands of glass are bonded with a resin-like compound in a door-shaped mold. The finished product is a door that's solidly constructed with hardened glass but still contains the flexibility of resin.
Another great thing is that fiberglass doors can be built to look like wooden doors on the surface but would not leave you being concerned about cracking and peeling that come from moisture and age. Fiberglass doors are also considered to be very durable and have warranties that go until 30 years. Fiberglass doors have but a single negative aspect and that is the fact that they're a little difficult to fix except for minor problems.
You may pick up more articles on fiberglass doors. Extra resources supplied for vinyl entry doors can be located here.