It's no wonder that decks have become so popular in the past 15 years - they add inexpensive living area to a home, increase the value of a home and provide a place where owners can relax, enjoy family activities and entertain.

A recent survey of 10,000 homeowners indicates that 21 percent of all U.S. households now have decks.Most decks and porches, whether built by a do-it-yourselfer or contractor, are constructed of wood. And 78 percent of the decks are built with pressure-treated lumber.

Pressure-treated wood is lumber that has been impregnated with a chemical preservative to make it resistant to attack from termites and fungal decay. The process dates back to 1875, but it was only with the development of the cleaner CCA treatment (chromated copper arsenate) that wood became suitable for use in decks and other residential applications.

CCA preservative extends the life of lumber without altering most of its other natural characteristics. The preservative is used in lumber yards around the world and is identified by various brand names. In North America, there are several regional products as well as international brands like Wolmanized and Outdoor.

Proper pressure treatment adds years of service to wood. Treated stakes set in the ground in Mississippi in 1945 have yet to fail, while untreated stakes lasted an average of less than four years.

That's a property of treated wood that continues to generate praise. Pressure treating conserves forest resources. Treated wood lasts for at least as long as it takes replacement lumber to be grown and cut.

On top of this, proponents note that treated lumber is made from plentiful species of trees - southern pine, ponderosa pine, red pine and, in the West, the hem-fir group. Old-growth forests in ecologically sensitive areas need not be harvested to obtain these trees.

Lumber has always been an environmentally sound choice as a building material - wood is the prime example of a renewable resource, and turning it into usable lumber requires less energy than alternate materials.

But concerns over chemical hazards have caused an increase of inquiries into the safety of pressure-treated lumber.

Bill Baldwin, vice president of technical and environmental services at Hickson Corp., says there is nothing to fear. "I have good news for those concerned about the safety of treated lumber. Wolmanized wood is harmless to people, plants and pets when used as recommended."

What are some of these recommendations?

1. Wear protective apparel when sawing treated wood, then wash hands and clothing after use.

2. Avoid inhaling sawdust or getting dust or chips in your eyes.

3. Wolmanized pressure-treated wood can be used indoors. It does not emit vapors or fumes.

4. Treated wood should not be used in direct contact with human food or drinking water.

5. Do not burn treated lumber, since it breaks the chemical bond between the wood and the preservative. There is a possibility of harmful chemicals in the smoke.

In laboratory tests and actual use over the years, the performance of treated wood has given manufacturers the confidence to provide lengthy warranties.

Not many products, especially structural building products, are backed by replacement warranties that extend decades into the future, but that's what the various producers of pressure-treated wood offer homeowners for residential uses. Warranties of 30 year and 40 years are common: the Wolmanized brand carries a "lifetime" guarantee.

The Environmental Protection Agency conducted a nine-year study of CCA-treated wood. "After all the investigative work, the agency declared that the benefits of CCA-treated wood outweigh the risks and suggested only moderate precautions," Baldwin said. "And most of the precautions are common sense and apply to both treated and untreated wood."

Copies of the EPA recommendations are available at lumber outlets.