By Joseph R. Polenzani
When most people hear the phrase “mobile home,” they immediately conjure up images of a small structure in a rustic setting, either standing alone or set up in a trailer park. Unless you live in the South or the Southwest, you probably don’t spend much time thinking about responding to fires in them. However, according to the year 2000 U.S. Census, almost eight percent of the housing units in the United States are mobile homes.1 In metropolitan areas (defined as those having a core population of 50,000 or more people), mobile homes account for just below six percent of the privately owned housing units. Communities of all sizes often share something else, too: staffing issues. Whether it’s a small volunteer organization, whose members are out of town during the workday; an understaffed suburban agency; or a larger city department enduring budget cuts and brownouts, fire departments must constantly find new ways to operate safely in less-than-ideal circumstances.
Rural fire departments, whose bread and butter are mobile homes and modular houses, have known for years what the latest fire research is telling us: With smaller crews and limited resources, an offensive interior attack is not always the best and safest way to extinguish a structure fire. When faced with a working fire in a manufactured home, consideration should be given to employing a transitional attack or a combination fog attack.
Despite their small size, mobile homes can present a number of challenges to firefighters. The average mobile home sold in the United States is only around 1,600 square feet, about one-third smaller than the average site-built home. However, federal regulations allow manufactured homes to be built as small as 400 square feet. To fit a “full-sized” life into these scaled-down homes, compromises must be made. Floor plans are designed to make maximum use of the available space, which often results in configurations unlike those found in larger houses. Hallways are narrower, and rooms may have less open floor space, making hose advancement difficult. Although the HUD code requires that finished interior surfaces have limited flame-spread characteristics, furnishings and contents are, by necessity, close together, which allows for rapid fire spread through direct flame contact or radiant preheating of nearby fuels. The compact nature of the structures also means that the effects of any sudden changes in a fire’s behavior or flow path will be concentrated in a smaller area. These possibilities were tragically illustrated in February 2009, when two West Virginia firefighters died after being overcome by rapidly moving smoke and hot fire gases while advancing a handline through a modified single-wide mobile home.
The transitional attack and the combination fog attack share the advantage of allowing a small crew (often only one or two firefighters) to safely control a fire from the exterior of the structure, thus buying time for other fireground activities, such as establishing a water supply, performing a search, or waiting for a sufficient number of personnel to arrive to make an effective direct interior attack. Both techniques also reduce or eliminate the need for vertical ventilation, which is rarely safe or practical on these lightweight structures. Let’s take a closer look at each of these techniques.
The modern transitional attack, as demonstrated in recent National Institute of Standards and Technology and Underwriters Laboratories fire research studies, consists of straight stream water application from the exterior of a fire compartment, banking the stream off the ceiling, to cool the interior and “reset” the fire to a preflashover stage or to prevent a smaller fire from reaching flashover conditions. This preliminary fire control is followed by coordinated ventilation and a direct interior attack on the seat of the fire.
Ideally, these exterior and interior attacks would be accomplished using two separate hose teams, especially in larger structures, where the fire room may be some distance from the nearest exterior door. However, the small size of mobile homes makes it more feasible for a single crew to hit the fire from the outside and then reposition the hose for interior work. Most mobile homes also lack the extensive landscaping, fences, and other obstructions that can prevent firefighters from getting up close to windows on the sides or rear of the house, to direct the fire stream into the compartment at the recommended acute angle.
The transitional attack is also an excellent option when there is a chance that the structure may still be occupied. Research has shown that managing the flow path and cooling the fire can reduce temperatures in uninvolved portions of the structure, making conditions more tenable for fire victims. This is an especially important consideration in smaller structures, such as manufactured homes, where trapped or incapacitated occupants will always be in close proximity to the fire and undersized windows make traditional search and rescue operations such as vent-enter-isolate-search (VEIS) more difficult.
The combination fog attack is a technique that has largely been ignored in recent years, as the fire service has focused on using straight or solid streams to conduct direct interior fire attacks. However, it still has much to offer smaller crews, especially those operating with a limited water supply. Although we typically think of water-supply issues as being a rural problem, mobile homes in urban areas are often located in trailer parks with narrow private “streets.” In these communities, laying a supply line to the nearest hydrant may block other apparatus from reaching the scene or even entering the park at all. Larger mobile home parks may also have private hydrants fed by the domestic water system, which should not be relied on for firefighting unless they are serviced and tested regularly. In either of these scenarios, the initial engine company may have to control, and possibly even extinguish, the fire with the water in its booster tank.
The combination fog attack was originally introduced to the fire service by Keith Royer and Floyd W. Nelson, based on research conducted at Iowa State University in the 1950s. And like the transitional attack, the method was refined and proven effective through hundreds of live burn evolutions. In modern fire textbooks, the combination attack is usually illustrated as being performed from inside a fire compartment using a straight or a narrow fog stream applied in a “T,” “O,” or “Z” pattern. However, Royer and Nelson originally conceived of the combination attack as a firefighting operation that would be performed from outside the fire compartment.2 The key to the combination fog attack is a quick and efficient distribution of water throughout the fire compartment. This is accomplished by using a wider fog pattern and “rolling” the stream around the fire compartment in a circular motion, applying water to the superheated overhead gas layer and the room’s surfaces and contents. As the water turns to steam, it absorbs heat and blackens out the fire. When done properly, the combination fog attack should require only a 20-30 second application of water. Continuing to add water after the fire has blackened down will result in condensation, upsetting the thermal layers and reducing natural ventilation.
Most firefighters are still familiar with the Iowa Rate of Flow Formula, despite the fact that the combination fog attack itself has fallen out of favor. The formula: Gallons per Minute (gpm) = Cubic Feet ÷ 100, is designed to be applied to a single open area when that area is fully involved (i.e., post-flashover). The HUD code requires that bedrooms designed for two people must contain at least 70 square feet. Using an average ceiling height of seven feet, our needed flow for a bedroom is only 4.9 gpm (490 ÷ 100). For a larger fire involving the main living and kitchen areas (40 percent) of an average 1,600 square-foot mobile home, the flow rate is still only 44.8 gpm (4,480 ÷ 100). It’s important to remember that the combination fog attack is designed to only knock down or temporarily control a fire. Full extinguishment will require additional water applied directly to the fire by a crew inside the building.
Neither of these techniques is applicable at every incident. Both methods require that the first-arriving fire crew locate and access the fire compartment. Both methods also require crews to quickly follow up the knockdown with a direct interior attack and coordinated ventilation. If the fire cannot be located from the exterior, it may still be necessary to search for the fire from inside the structure and mount a coordinated interior attack. As Royer noted, “Points of access for [water] distribution should be established before the fact. Doing this enables you to conduct a size-up and develop plans for using a direct, an indirect, or a combination attack to achieve the best distribution of water using fog or straight streams.” Firefighters need to understand the latest developments in the fire service and those techniques that have stood the test of time. Whether the structure is a mobile home or a site-built house, sizing up the situation and choosing the appropriate tactic give us the best odds for success.
1 The term “mobile home” refers to transportable factory-built houses constructed prior to June 15, 1976, the effective date of the National Manufactured Home Construction and Safety Standards Act of 1974 (also known as the “HUD Code”). Newer units are properly termed “manufactured homes.” However, with a life expectancy of 30 to 55 years, firefighters are likely to encounter both versions in the field. For the purposes of this article, the terms will be used interchangeably.
2 Although Royer and Nelson called their method the “combination attack,” I use the term “combination fog attack” to differentiate between their technique and the newer version.
Joseph Polenzani began his career in the fire service 23 years ago as a volunteer firefighter with the Ashland City (TN) Fire Department. He spent 10 years with the department, the last four as a captain. In 1998, he became a full-time firefighter with the Franklin (TN) Fire Department. In the past 16 years, he has served as a rescue company firefighter, a truck company lieutenant, an engine company captain, and an administrative services officer. He is chairman of Franklin’s training committee and is a recruit school instructor. He has developed and taught numerous classes for the department’s state in-service training program. He has a bachelor’s degree in fire administration and is a state-certified firefighter II, apparatus operator, fire officer II, safety officer, and instructor. He has also earned numerous certifications in technical rescue and is a Tennessee EMT-IV.