BY JOSEPH T. BERRY
Fires that originate from the exterior of a structure featuring combustible construction material seem to be more frequent today. Why are they happening more often? People spend more time today enjoying the outdoors whether it’s a barbecue on a sprawling deck, rejuvenating flowerbeds around the house with fresh mulch or chips, relaxing in a spa on the deck, or enjoying the warmth of a fire pit on those cool autumn nights. These innocent human activities do not seem to present any fire threat, but they can contribute to a devastating event. In the fire service, we take a commonsense approach; but, unfortunately, common sense is not common.
Size-Up and Concerns
On arrival, the most important initial size-up is determining the fire’s location and how it is extending. A fire that starts outside and is extending into the structure’s interior must be recognized immediately. A 360° size-up around the perimeter of the structure will confirm that.
Most interior fires originate from the improper or careless use of electric items (heaters, hot plates, power/extension cords); smoking materials such as cigarettes; open-flame items (candles, incense, stoves, cooking grills); or poorly maintained heating equipment. From a fire safety standpoint, the inside of the home should be protected with a dual-powered smoke/carbon monoxide (CO) detection system positioned in the right location on each level to provide an advance warning to the occupants in a fire.
But what type of detector exists for a fire starting outside? Presently, there is no detection system for the exterior of the home that is affordable for the consumer. A fire that originates from the outside and communicates directly to the exterior of the structure creates an extreme life hazard for the occupants inside (an outside/in fire). In the worst-case scenario, it would prevent the occupants’ escape by the primary and secondary exits. The fire service recommends that homeowners and renters formulate a viable escape plan in the event of a fire. But will an interior escape plan cover this type of outside/in fire? What if this occurs at night while the occupants are sleeping? The end result can be devastating.
Outside/In Fire Incidents Carmel, New York, May 1, 2012
This type of private dwelling of lightweight construction is prevalent throughout the United States. This newly built wood-frame home features a truss roof and floor system, oriented strand board (OSB) sheathing wrapped with an air/moisture barrier, and vinyl siding. From the outside front covered porch, the front door entry opens into a vaulted foyer with a high ceiling, and stairs lead from the foyer to the second-floor bedrooms, including the room above the garage (photo 1).
A fatal fire incident involving such a structure occurred in 2012 in Carmel, New York; it killed four people. The fire started from a clipped cigarette ash, which smoldered for hours in a chip bed by the front porch. A dry spring morning with low humidity and a slight breeze offered ideal weather conditions that combined with the above factors for the perfect storm.
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| Photos 1-3 courtesy of Putnam County (NY) Fire Marshal. |
The fire went from the incipient to the free-burning stage, communicating to the vinyl lattice attached to the face of the front porch. An evergreen shrub was in this vicinity also. The fire extended through the wood joist bays under the porch platform toward the exterior facade of exposed OSB house sheathing. As the fire grew, the vinyl siding and the air/moisture barrier melted and exposed the OSB sheathing, and the fire consumed the structure’s front porch and façade. The fire traveled unimpededly vertically, melting the perforated vinyl soffit vents and extending into the attic/truss loft area. An attic/truss loft area is a lumberyard of additional fuel.
Once the fire enters this confined space area, anyone asleep in the upper bedrooms is in an extreme, life-threatening situation. This house’s construction included roof and floor trusses, which can collapse within minutes when exposed to a free-burning fire, thus compromising the roof and floor structures.
On arrival, firefighters encountered a heavy volume of fire and a fully involved structure exterior. The Carmel Fire Department chief stated, “We were dispatched to a possible rescue, people trapped inside. It became quite apparent that there was to be no attempt for an interior attack.” The rear wall collapsed first, the side wall on the right side of the house collapsed next, and then the roof came down. All this happened in 10 minutes (photos 2, 3).
New Windsor, New York, January 9, 2015
This house was recently completely rebuilt from top to bottom. The first-floor front of the house was finished with textured stone and a combination of wood 1 × 6 sheathing covered with vinyl siding around the rest of the structure. All dimensional lumber was used for the floor and roof systems, and the front family room had a high vaulted ceiling.
The fire started in the front of the structure under a covered roof area at the right side of the front of the house (photos 4, 5). A plastic dog house with a thermostat-controlled heating pad connected to an extension cord was under this shed roof. The dog house was on a cement slab between three front windows. The covered shed roof was open on two sides. The outside walls of the house provided wall coverage on the other two sides. On the morning of the fire, the temperature was 11°F; a steady wind out of the west was gusting at more than 20 miles per hour. Everyone was asleep except for the wife, who was working on the computer. She got up to get a glass of water, heard a crackling sound, and noticed a glow in the two front windows. She woke up the rest of the family. At that time, the two front windows failed; then the third window failed. The intensity with which the fire entered the interior of the structure was like a blowtorch. The family had just enough time to escape with the clothes on their backs. The fire originated in the area of the plastic dog house. The gusting wind induced fire growth, so it was a wind-driven fire. If everyone had remained asleep, the result could have been devastating.
Building Materials Vinyl Siding
Vinyl siding is comprised mainly of polyvinyl chloride, commonly known as PVC. Because of its chlorine base, vinyl siding does not ignite quickly and is inherently flame retardant. PVC won’t ignite, even from another flame, until it reaches about 730°F (387°C) and won’t self-ignite until 850°F (450°C). Those ignition temperatures are significantly higher than that of framing lumber, which ignites from flame at 500°F (260°C) and self-ignites at 770°F (410°C).
ASTM International’s D2863, Standard Test Method for Measuring the Minimum Oxygen Concentration to Support Candle-Like Combustion of Plastics (Oxygen Index), tests show that rigid PVC’s high limiting oxygen index means it usually needs large amounts of oxygen to burn and stay burning. Rigid PVC (vinyl siding) will not independently sustain combustion in air with a normal concentration of oxygen (about 21 percent), so it extinguishes more easily.
OSB Plywood
OSB is an engineered wood-based panel consisting of strands of wood that are bonded together with a synthetic resin. The strands are pressed together in layers. The wood species used in manufacturing include soft woods (aspen, poplar, southern yellow pine); other mixed hardwoods may be used. The resin types include phenol formaldehyde, melamine-fortified urea formaldehyde, and isocyanate, all of which are moisture-resistant barriers.
OSB plywood has an autoignition temperature of 400°F to 500°F (204°C to 260°C), is stable, and should not be exposed to open flame. The by-products of thermal decomposition include carbon monoxide, carbon dioxide, aliphatic aldehydes, rosin acids, terpenes, and polycyclic aromatic.
Trusses
Roof and floor trusses are connected with gang plate fasteners and, when exposed to a free-burning fire, can collapse in less than five minutes. A test performed on wooden I-joists comprised of OSB web members exposed the I-joists to a free-burning fire. Flashover occurred five minutes, 15 seconds (5:15) after ignition; floor collapse occurred 8:34 after ignition. The floor platform time to collapse was 3:19 after ignition.
Legacy vs. Today’s Construction
Much of today’s new building construction does not protect the outside of the structure adequately in the event of a fire originating from an outside source. Vinyl siding, air/moisture barrier wrap, and OSB are popular low-maintenance exterior coverings for today’s structures. The skeleton frame is using more young-growth pine, a lighter, less-dense lumber in today’s single-family homes and multifamily townhouses. Douglas fir was more prevalent in older (legacy) framed homes. One young-growth tree found on the East Coast, southern pine, is harvested for lumber in approximately 30 to 50 years. Older-growth trees like Douglas fir, found in the Northwest, may be harvested in 100 years or more. Denser, older-growth lumber does not burn as quickly as the less-dense, young-growth lumber. The demand for lumber today and the shortage of natural resources have resulted in the creation of new engineered wood products in today’s building industry. Under normal conditions, this method of exterior encapsulation by itself does not pose a problem. The concern is when a small fire grows on a combustible surface and extends to the exterior of the structure, as was the case in that fatal fire in Carmel.
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| Photos 4 and 5 by author. |
Older existing construction also has the same potential for ignition from an outside fire, and numerous fires and fatalities have occurred over the years. The difference between an older legacy home built with dimensional lumber vs. a newer one built with lightweight construction using a truss system is the earlier collapse of the structure once the fire communicates into the structural components of trusses for the roof or floor system.
Many Sources of Ignition
The sources of ignition in outside/in fires are many: discarded tobacco ash in mulch beds; hot ashes from a wood-burning stove/fireplace discarded too close to the structure; a storage shed built under a deck close to the house for a lawnmower and fuel; a spare propane tank; an extension cord from the house that provides the shed with light; improperly installed walkway lights in a mulch bed; improperly installed outlets; oily rags left out in the sun near the deck after applying a fresh coat of stain; combustible contents; furniture stored on decks, porches, or patios; a metal or plastic garbage can stored against the house; tall dry grass around the house perimeter; cigarette ash in wood chips contained in plastic flower pots stored against the house; and firewood stored against the house ignited by a discarded cigarette. These are just a few sources of ignition from past fires.
The weather can also provide the right ingredients for fire growth. During a dry period with low humidity, a slight breeze or a gusty wind can increase the velocity of the fire tenfold.
When the flame spread extends to the outside of the structure, it initially is a surface-burning fire for a very short time. As the fire spreads upward, it melts away the vinyl siding and air/moisture barrier wrap and exposes the exterior sheathing. Once the sheathing ignites, the fire intensity increases and produces an enormous amount of energy very quickly. The square footage of the exterior surface area burning determines the amount of radiation being transferred.
Radiation travels in straight lines. During a recent outside house fire, a neighboring structure 150 feet directly across from a fully involved structure sustained heavy damage to the vinyl siding. Initially setting up a tower ladder or pumper deck monitor in front of that burning building can cost your department the price of a new apparatus. Flanking on the sides away from the direct path of the radiant heat would be a prudent tactic.
If exterior windows are in the direct line of fire travel, an open window or a failure of glass will allow extension to the interior. Once the fire energy extends to the interior from the outside, it will travel like a speeding locomotive, consuming additional highly combustible home contents.
The topography of the interior will have a bearing on how fast the fire extends in the interior. The open-concept layout enables a rapid extension, whereas an older compartmented interior layout will delay extension for a short time. An open interior staircase creates an excellent vertical shaft for heated convected gases to extend to the upper levels. A fire in the roof attic/truss loft area is a different situation and is similar to a cockloft fire. This is a critical stage of the operation. The whole floor area below is affected. The pressurization of smoke and gases in this confined space will cause a violent flashover. Roof trusses will fail, and collapse is imminent.
Fire Tactics Points to Ponder
- A 360° size-up is a must to determine the fire’s location and where and how it is extending.
- Remember, more lives are saved by the proper hoseline placement than by any other means. Addressing the outside fire is paramount, depending on what stage the fire has reached. The first-due engine company should stretch two handlines simultaneously on arrival.
- Attack from the sides, not directly in front, and avoid breaking windows with the hose stream.
- If the windows are already broken and the fire has already extended inside, direct a rapid sweep with the hose stream at the ceiling level. If the fire has extended into the vinyl soffit eave vent, direct the hose stream into the soffit opening. Keep the angle of the hoseline parallel with the roof angle.
- If the outside deck and sheathing are involved, a fast knockdown with the handline will buy some time for a possible interior search and rescue using the second handline to protect and evacuate the occupants. You must coordinate this with the outside line operation.
- Consider initially using the booster tank water for a fast outside knockdown. Using 500 to 1,000 gallons of tank water, you can knock down a lot of fire if you use it right. Remember, this is just for a fast knockdown. You must still establish a viable water supply before entry.
- An interior rescue operation might not be feasible, so ensure portable ladders are present and ready if occupants are trapped and visible from the exterior windows. Time is of the essence, so use a hose stream in combination with a portable ladder for rescue. Remember, LIFE is the number one priority.
- With lightweight construction, you have a short window of operating time for a collapse once the fire has communicated to the structural components-the house sheathing, the floor and roof trusses, the wooden I-joists, the exposed dimensional wood floor joists, and the roof rafters.
- If using high-caliber streams, be prepared for a building collapse. Before operating the streams, account for all fire personnel, and remove all members from the perimeter of the collapse zone.
- In the worst-case scenario, as in the Carmel fire, the structure may be fully engulfed in flames on arrival, and it is unlikely anyone inside would be alive at this point. But still conduct a 360° perimeter search. There just might be a savable life at a front, a rear, or a side window.
- Although it goes against the firefighter’s grain, with lightweight construction, we cannot always save property as in the past. Our exclusive strategy must be saving life, evacuating everyone safely, and protecting the exposures.
- You must have your strategy and tactics plan set up beforehand because of the speed and the intensity of fire extension and the collapse potential. Conduct drills using different fire scenarios, and train regularly on lifesaving tactics.
- Fires are more intense and temperatures reach unprecedented levels in minutes after flashover-from 1,000°F to 2,000°F-because of the contents found in the average home today.
- Employing these operational tactics depends on having enough firefighters, officers, and chief officers on the scene to accomplish them. The houses today are larger in square footage. Follow National Fire Protection Association recommendations for a sufficient number of fire personnel for operations. Between 19 and 23 personnel typically constitute the first-alarm assignment to a confined single-family dwelling fire. These numbers increase according to high life hazard or type and size of occupancy.
JOSEPH T. BERRY, a 31-year veteran of the Fire Department of New York (FDNY), retired as a lieutenant in 2002. He was a firefighter with Engine 1 and Ladder Company 24. Promoted to lieutenant in 1983, he served with Engine 73 and then Ladder 42 until his retirement. Berry served on an FDNY committee that revised the probationary firefighter’s manual and the standard operating procedures for firefighting in tenements, brownstones, wood-frame buildings, and lightweight residential construction. He has written numerous articles on building construction and firefighting. Berry was a consultant for Titan Corporation/Department of Homeland Security.
Fire Safety Recommendations
During Fire Prevention Week, educate the public on fire safety and the hazards of the outside/in fire. Below are some fire safety tips. Note: Applicable local, municipal, and state fire codes take precedence when they conflict with the recommendations below.
Reevaluate your family escape plan. An outside/in fire is a different type of fire because there is no outdoor warning system in place. Educate your family about the fire prevention checklist above. If we know the causes of these fires and their devastating effects, we can eliminate the hazards. If fire does occur, evacuate everyone to the outside of the premises immediately. Keep in contact with the 911 dispatcher until the first-arriving unit is on the scene.
Once it is confirmed that all family members and other occupants have evacuated the structure, the homeowner (occupant/renter) is responsible to verbally communicate this fact with the first-arriving fire unit. A young firefighter lost his life searching for occupants who had already self-evacuated; the first-arriving unit was not informed of their self-evacuation. If a member of the family or an occupant has not been accounted for, verbally communicate this to the first-arriving officer/firefighter along with that person’s last known location, name, and age.
These types of fire are extremely treacherous; you must exit the house immediately and exit away from the fire.
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