Safety rules for wood-and coal-burning stoves

A fire that badly damaged a home last year began with ''startling suddenness, '' to quote the occupants. But the fire chief whose crew was called to the blaze voiced a dramatically different opinion: ''This fire,'' he said, ''began 10 years ago!''

A decade earlier a wood-burning stove had been installed in the house. It was a well-made stove, set on a masonry base, and was vented into a structurally sound chimney. But it had been installed incorrectly in one important respect: It was closer than the mandatory three feet from an unprotected combustible surface, in this case some wood paneling.

At the time the distance seemed more than adequate. Temperatures reaching the wood surface, even when the stove burned its hottest, never seemed high enough to start a fire.

The assumption was true enough. Under normal circumstances wood ignites only at higher temperatures than those reaching the paneling from the stove. But something happens to wood when it is subjected to high temperatures over a long period of time. It is chemically altered by a process known as pyrolysis. In simple terms it degrades to the stage where it will ignite readily at much lower temperatures.

The point to remember, under these circumstances, is this: Just because the wooden wall, or piece of furniture, did not catch fire last year does not mean that it won't this year.

House fires that have their source in a wood- or coal-burning stove have been on the increase since Americans turned to them by the thousands in the past decade as a supplemental source of heating. But it is seldom the stove itself that is the problem, notes the New York-based Insurance Information Institute; rather it is the people involved. They either install the stove improperly or use it in an unwise or careless manner.

In many respects a sort of ''generation gap'' is involved - in that an entire generation in the United States and Western Europe was never exposed to wood- and coal-stove use. To help fill the information void the institute brought out a free pamphlet, Wood Stove Safety.

The message it contains is this: Wood- or coal-burning stoves can be operated effectively, safely, and with ease if just a few basic rules are adhered to. You can even place a stove much closer to a combustible surface if a noncombustible shield is placed in between. Here are some of the basic points brought out in ''Wood Stove Safety'':

Chimney. Before installing a stove, have your chimney checked by a competent mason. Flawed chimneys can be relined with poured masonry or a stainless steel liner. If you don't have a chimney, double-wall stainless steel chimneys can be readily installed in an existing house.

Stove. Be sure your stove is made of a reliable material such as cast iron or steel plate. Soapstone or tile are even better materials. See too that the stove is listed by Underwriters Laboratories or another recognized testing lab. Check legs, hinges, grates, and draft controls for cracks and other defects if you buy a used stove.

Placing. Site the stove on a masonry or other fire-proof base. See that the stove itself is 36 inches away from any combustible surface and that the stovepipe leading to the chimney is 18 inches from such surfaces. These distances can be lessened if a shield of metal (aluminum is particularly good because it reflects radiant heat so well) or some other non-burnable material is placed or mounted at least one inch from the wall. This way, air that heats up immediately behind the shield convects upward and is replaced by cooler air in a constant cycle.

Other recommendations from the institute are:

* Clean out stovepipe elbows, joints, and flues as well as the chimney before starting your first fire of the season. Make use of a professional chimney cleaning service unless you are a competent do-it-yourselfer.

* Burn well-seasoned wood (trees felled six months or more).

* If yours is a tight house, consider opening the window a crack for ventilation. In homes under construction, have outside air brought directly to the base of the stove.

* Dispose of ashes in a closed metal container outside the home.

* Don't connect a stove to a chimney already serving another appliance burning other fuels (gas- or oil-burning furnaces, for example).

* Don't let a fire burn unattended overnight.

* Don't burn trash in a stove (doing so can start a chimney fire).

For a free copy of ''Wood Stove Safety'' send a stamped, self-addressed envelope to Insurance Information Institute, Publications Service Center, Department WWS, 110 William Street, New York, N.Y. 10038. The institute also has a toll-free insurance hot line: 800-221-4954.