CWC- Canadian Wood Council

HPVA- Hardwood Plywood and Veneer Association, 1997

HPVA2- Hardwood Plywood and Veneer Association, 2000

UL- Underwriter’s Laboratory

(a) Due to wide variation in the species of the pine family and some confusion due to common (local) names, exact identification of the types of pine tested was not possible. The effects of differing climate and soil conditions on the burning characteristics of given species have not been determined.

(b) In 18 tests of Ponderosa Pine, 3 had values over 200 and the average value of the rest was 154.

The enactment of codes requiring installation of smoke detectors has resulted tremendous improvement in fire safety, but whithin the past 10 years injuries and deaths have increased in hme in which smoke detectors wee installed but were inoperable.

Smoke detector placement may vary with local jurisdictions, but in general, they should be placed to protect sleeping areas. It’s a good idea for inspectors to know local requirements and include in the Inspection Report narratives which mention smoke detector placement and maintenance, especially if detectors are battery-operated instead of hardwired.

• The fire death rate in homes with working smoke alarms is 51% less than the rate for homes without this protection.
• 65% of reported home fire deaths in 2000-2004 resulted from fires in homes with no smoke alarms or no working smoke alarms.
• Why do smoke alarms fail? Most often because of missing, disconnected or dead batteries. Nuisance activations were the leading cause of disabled smoke alarms.

                                                                                         –National Fire Protection Association

In addition to smoke detectors, inspectors should understand what is appropriate for their area in recommending fire mitigation such as creating zones of defensible space.

Defensible space is an area around a structure within which fuels and vegetation are treated, cleared or reduced to slow the spread of wildfire towards the structure. It also reduces the chance of a structure fire moving from the building to the surrounding forest.

In log homes built on homesites remote enough that response times for the local fire department are bound to be long, inspectors might consider the inclusion of a report narrative which mentions the advantages of installing a fire suppression system.

A fire suppression system is one which applies a smothering, non-combustible substance (water, foam, dirt, etc.) which isolates fuel from the oxygen required for continued combustion.

In areas where wildfires are a significant hazard, fire-proof roof coverings and sprinkler systems which protect combustible roof covering materials are common options.

In fighting a rural fire, the fire department needs more water volume than can be supplied by connecting to the home water supply through an exterior faucet. If a home has no fire hydrant or stream nearby, the fire department will typically depend upon water supplied by fire department tanker trucks which can carry up to 15,000 gallons on board.

At about 7 lb. per gallon, water is heavy (15,000 gallons weighs about 50 tons), and the trucks required to haul water are heavy. Roads, bridges and driveways which provide the approach to a home will need to be constructed and maintained in a manner which will allow fire department pumper and tanker trucks to use them.

Inspectors can recommend that their client consider the installation of a cistern, which is an underground tank, but cisterns are often ineffective for the following reasons. 

Upon arrival at a structure fire, if everything goes right, the time required for a pumper truck to connect to the cistern, prime the pump and begin putting water on a fire can easily be 10 to 15 minutes.   

Depending on the homesite, locating the cistern far enough from the home to allow truck to approach it may be difficult. If a cistern is located in front of a home it won’t be used because firefighters don’t park their equipment in front of burning buildings.

Minimum cistern tank sizes as established by local jurisdictions are not always rooted in reality. It’s not unusual for a minimum tank size to be 500 gallons. Modern fire trucks pump water at a rate of about 300 gallons per minute (GPM), which provides 1½ minutes of water for a home using a tank meeting the minimum requirements. 1½ minutes of pumping may extinguish a car fire, but unless it’s in the very early stages…not a structure fire.

To provide about 30 minutes of pumping at 300 GPM,  a 10,000 gallon cistern would need to be installed at a safe distance from the home.

The Urban Wildland Interface Code stipulations for water supply are as follows:

• 1 or 2-family dwellings not exceeding 3600 square feet must provide water supply capable of providing 1000 GPM for a minimum of 30 minutes.
• 1 or 2-family dwellings of 3600 square feet or greater must provide water supply capable of providing 1500 GPM for a minimum of 30 minutes.

Exception: A reduction in required flow rate of 50%, as approved by the code official, is allowed when the building is provided with an approved automatic sprinkler system. 

The Urban Wildland Interface Code MENTIONED ABOVE was developed and made available by the International Code Commission (ICC) starting in 2003. This code is in use in certain jurisdictions only and inspectors making comments about fire-safety requirements should take steps to determine what fire-related codes or regulations apply to the area in which the subject property is located.

Exposure of wood to fire causes thermal degradation or pyrolysis of the wood in which wood is converted to char residue and volatile gases. The amount of damage depends on both the temperature and the duration of the exposure.

Below 212° F- for a short exposure, the mechanical effects are reversible.

Above 150° F- Prolonged exposure can result in permanent strength loss.

Under 392° F-  Charring requires prolonged exposure.

392° F to 572° F- Significant degradation occurs.

550° F to 842° F- vigorous flames

As wood burns, there’s a steep temperature gradient across the outer layers of wood, with the hottest part at the log outer surface and the coolest part toward the interior of the log.

A “steep temperature gradient” means that although the surface of the log may be very hot, temperatures only a short distance into the log into the log will be much cooler.

The gradient might look something like this…

550° F - Temperature at the log surface.

350° F –  ¼-inch deep into the log.

220° F –  ½-inch deep into the log.

The char rate for logs is approximately 1½ inches per hour when exposed to the standard ASTME 119 (ASTM International 2007) fire exposure, which involves specific durations at specific temperatures.

Char rates will vary with wood species, density, moisture content and duration of exposure.

As mentioned, logs contain a steep thermal gradient, and the loss of strength in logs is related to the duration of exposure to temperatures high enough to cause strength loss.

This means that strength loss only occurs to portions of the log a short distance inward from the char layer. A thick log may experience a significant amount of heat and charring at its exterior surface and still retain significant or full strength in a large portion of its remaining wood.

If only the outer layers of wood in a log have gotten hot enough to lose strength, the inner portions will still have significant load-carrying capacity.