Avoid Potential Fire Hazards at Your National Historic Landmark

White building on fire.
Old capitol Building on fire, Iowa City, Iowa.

Photo courtesy of Old Capitol Museum.

In the past several years, two of the National Park Service Midwest Region’s National Historic Landmarks (NHLs) have been severely damaged by fire as a result of using heat-producing tools during renovation projects.

On November 21, 2001, the Old Capitol Building NHL in Iowa City, Iowa, suffered a fire that destroyed the building's 160 year old cupola, dome, and bell. The State Fire Marshal ruled that the fire was started accidentally by workers using hand torches or heat guns to remove asbestos.
Brown building on fire.
Jefferson County Courthouse on fire, Madison, Indiana.

Photo courtesy of Robert Maile.

On May 20, 2009, John Stacier, Executive Director of Historic Madison, Inc./Historic Madison Foundation, Inc., wrote the NPS, “As I write this, the Jefferson County Courthouse, built 1854-55, is suffering a devastating fire. The entire roof is gone, though as I last saw it the barrel and dome were still partly standing - the lantern at the top was destroyed earlier this evening.” Several weeks later, Mr. Stacier reported that officials determined the cause as a “propane torch used in soldering the new copper downspout to the box gutter had ignited [the] underlying wood structure.” The Jefferson County Courthouse in Madison, Indiana, is a contributing building in the Madison Historic District NHL.
Two men on scaffolding removing paint from a wall.
Workers on scaffolding carefully remove deteriorating paint with heat guns.

Photo courtesy of Alan O'Bright, NPS Tech Note No. 18.

The NPS’ Technical Preservation Services (TPS) provides excellent advice on a variety of preservation issues, and may be found online as “Preservation Briefs” at https://www.nps.gov/tps/how-to-preserve/briefs.htm, and as “Preservation Tech Notes” at https://www.nps.gov/tps/how-to-preserve/tech-notes.htm. Regarding paint removal, the use of heat (blow) torches is specifically not recommended. Along with a discussion on the treatment of paint problems in historic buildings, Preservation Brief No. 10: Exterior Paint Problems on Historic Woodwork, includes information on the justification for paint removal, paint removal precautions, re-painting historic buildings for cosmetic reasons, and identification of exterior paint surface conditions and recommended treatments.

The TPS also provides information on paint removal from wood siding in Tech Note No. 18: Paint Removal From Wood Siding, using the Truman Home at the Harry S. Truman National Historic Site, in Independence, Missouri, as an example:

“Thermally removing paint using a heat gun does carry certain fire risks that require precautions both in the planning as well as in the execution of the work. With an ignition temperature of approximately 200-250°F, the wood itself can ignite from the hot air blast, leading to potentially serious fire damage to the historic building."

In assessing the risk of the wood igniting, a number of factors need to be taken into account. The moisture level of the wood definitely affects the temperature at which the wood ignites. Wall studs behind the siding that are adjacent to high temperature heating pipes would be very dry compared to the siding. If the heat from the gun did not dissipate fast enough within the wall cavity, studs or deadening boards could begin to smolder in particularly hot spots or areas of very dried wood, even though the siding is not immediately affected. And where there is insulation in the wall, heat build-up would be greater, thereby increasing the fire risks. Even the daytime temperature and prevailing breezes need to be considered, since cooler temperatures and a mild breeze will help cool the siding faster. On the other hand, strong winds will make it more difficult to remove the paint, increasing the fire risks in a variety of ways.

Another factor to be considered is the surface condition of the siding. Very rough edges are more susceptible to ignition than smooth surfaces. A more common problem that must be taken into account not only in planning but also throughout the work is the tendency of the laborers to get impatient or careless, directing the heat gun in one spot too long or adjusting the heat gun to a higher temperature.

In addition to the possibility of igniting the wood, there is the even greater risk of ignition of flammable debris commonly found in wall cavities and behind cornices. Debris such as bird and rat nests, builder’s trash, accumulated dust, and building material waste can all be more flammable than the wood siding. Examining selective areas of the wall cavity and cornices prior to selecting a paint removal method can establish the extent of potential fire risk from debris and building material.

Additional precautions need to be taken in the course of work. Both the work crew and park staff at the Truman home were thoroughly familiarized with the fire risks involved. Besides using scrapers or chemical strippers in the areas of highest risk, workers were instructed to avoid overheating the wood. This tends to occur at uneven wood surfaces, such as found in decorative trim or in cornices. Since workers tend to get overly confident and very casual as the job proceeds, someone on the crew should be assigned responsibility as the “fire-safety inspector.”

Suitable fire-fighting equipment should be readily available. At the Truman home, carbon dioxide and water fire extinguishers were within immediate reach of every workstation where a heat gun was being used. The contractor added glycol to the water extinguishers during cold weather work to prevent freezing. In addition, a long garden hose was kept near the work site during warm weather.

Since debris and wood will tend to smolder for a number of hours before breaking out into flames, the building should be equipped, if possible, with a temporary fire detection system in the attic eaves and adjacent to exterior walls. Furthermore, paint removal using heat guns should stop at least several hours prior to the site being vacated each evening, to increase chances of early detection of any smoldering fire. The area of the day’s work must be carefully inspected. And finally, if there is a night watchman, extra diligence should be demanded during the weeks when paint removal is occurring.”

While it is important to understand the risk-factors involved in rehabilitation and/or restoration projects, it is also important to consider including restrictions in the specifications of the contract. Such restrictions could forbid the use of open-flame torches, heat guns or heat plates, or include specifications for the use of those tools. Another restriction could forbid smoking at the job site. The specifications could also require after-work hours monitoring of sites that could have been put at risk for fire caused by the use of heat tools.
Originally published in "Exceptional Places" Vol. 4, 2009, a newsletter of the Division of Cultural Resources, Midwest Region. Written by Michele Curran.