Water as an Effective Fire Suppression Agent
Water has been used for fighting structural fires in America since the first fire department was organized in New Amsterdam, which was renamed New York City in 1664. Water is the agent of choice for structural fire suppression for many reasons: (11) The general ability of water from fire hydrants in communities that have a municipal water system.
The general availability of water in suburban and rural areas without fire hydrant service from farm ponds, wells, small lakes, creeks, streams, and, in many locations larger rivers and lakes.
These water sources can be used to provide separate water supplies for structural fire suppression, as discussed in Chapter 10.
These water resources also can be used with dry hydrants to refill mobile water tankers and transport water to fire sites or, where feasible, by use of mobile pumpers that can be used to pump water directly to fire sites.
Water is the least expensive of all the types of fire extinguishing agents currently available.
It is available in a liquid state over a wide range of temperatures extending from 32 °F (0 °C), to 212 °F (100 °C), or the boiling point of water.
Both treated and untreated water are generally considered safe to use in human and animal environments when properly applied through sprinkler heads or fire department nozzles.
It is most normally selected to control and extinguish structural fires because its nontoxic, noncorrosive, and is stable over a wide range of conditions. This means that when water H2 O is applied to a developing fire in ordinary combustible materials, the water does not break down into the basic elements of Hydrogen (H) and Oxygen (O), both of which would encourage fire growth.
Water can be applied to building fires while occupants are still in the building under approved firesuppression techniques. This is not the case with some gaseous extinguishing agents, which may cause asphyxiation or adverse health side effects. The Physical Properties of Water It is essential that community officials, including the chief executive officer and staff, along with the water superintendent and fire chief understand the physical properties of water the permits the use of water as an effective fire extinguishing agent. The fundamental considerations include the following, documented by the NFPA. (2)
[Sidebar: The term “structure” is used in this Chapter to denote both unoccupied and occupied buildings for the sake of simplicity. Model building codes generally reference structures as being unoccupied and buildings as being generally occupied. This distinction will be made where the water application could be injurious to occupants still in a building when the initial fire attack is made on a developing fire.]
1) At ordinary room temperatures in a structure, water exists as a stable liquid. Water viscosity in the range of 24 to 210 °F remains constant, which allows water to be transported in water mains and pumped by fire department pumpers through fire hose.
2) Water has a high density, which allows it to be discharged from fire hose lines with nozzles and projected into structures on fire. Water’s surface tension allows it to exist from small droplets to a solid stream.
3) The latent heat of fusion is the amount of energy required to change the state of water from a solid (ice) at 32 °F to a liquid. Water absorbs 143.4 Btus per pound in this process.
4) The specific heat of water is 1.0 Btus per pound. Therefore, raising the temperature of 1 pound of water180 °F from 32 °F to 212 °F requires 180 Btus.
5) Water is an effective cooling agent because of its high latent heat of evaporation (i.e. changing water from a liquid to a vapor) which is 970.3 Btus per pound as will be described below.
6) Water expands in its conversion from a liquid state to a vapor state from 1,600 to 1,700 times the liquid volume. One gallon of water produces 223 cubic feet of steam. Therefore, it follows, that 1 gallon of water at room temperature applied to a fire and converted to steam (complete conversion) will have the following results.
a) Heat required to raise the temperature of water to boiling: 212 °F – 68 °F (Average room temperature) = 114 °F. 114 °F × 1 Btu/lb × 8.33 (Weight of 1 gallon of water) = 1,200 Btu.
b) Heat required to change water from a liquid to a vapor: 970.3 Btu/lb × 8.33 = 8,083 Btu
c) Total heat absorbed is 1,200 Btu + 8,083 = 9,283 Btu/gallon of water The above concepts are extremely important to effective fire suppression as can be observed in the following example. A fire department hand-held hose stream discharging 100 gpm could have the potential capability to absorb 928,300 Btus per minute in a complete conversion from a solid state to complete steam conversions; this represents 100 percent effectiveness of using water to extinguish fire through both absorbing heat and oxygen displacement. This is realized by recognizing that the same fire department hose stream has the capability to create 22,300 cubic feet of steam in the conversion process. To achieve this capability, water has to be applied in the form of a fog stream with finely divided particles in contrast to solid fire streams supplies by a tapered nozzle. A solid fire stream has been determined from numerous structural fire tests by the Western Actuarial Bureau to have only 10 percent or less of the cooling capacity of fog steams. In fact, 90 percent of the water applied from solid streams results in runoff with little or no extinguishing capability and may just do water damage inside a structure fire. (11)
All of this explains why the effective progress of a fire attack on a developing structure fire can be estimated and evaluated by observing the volume of smoke and condensing steam coming from the involved building. This has to be emphasized in the training of fire suppression personnel and especially in the training of tactical fire officers. Fire suppression personnel should be acquainted thoroughly with the characteristics of condensing steam and be able to evaluate the information it conveys on the fireground. Condensing steam can be observed and recognized instantly when projected against the sky. It is visible to the human eye in daylight or darkness. Observe a picture of the old steam locomotives when exhausting steam; the live steam is invisible as it comes from the exhaust valve. However, as it expands and loses some of its heat, the process of condensation begins and the expanded cloud of steam becomes visible. Condensing steam contains insufficient heat to cause physical injury. This has been used as a concern for not using fog nozzles to generate steam. To avoid any possible injury from steam generation at structure fires, the following three prerequisites are essential:
1) Fire suppression personnel needs to be trained to stay close to the ground or floor level where the attack is initiated since the steam will rise to the highest point of the enclosure.
2) Immediately after the initial fire attack, ventilation is required on the floor above the fire level or at the roof level for single-story structures.
3) Complete personal protective clothing is required for all fire service personnel making the fire attack; this includes self-contained breathing apparatus (SCBA) and the helmet ear flaps need to be down after the face piece is in place. Above all, training fires need to be extinguished before attempting a real-world fire attack on a structure that could produce volumes of steam.
When all of this is in place, structural fire suppression effectiveness will significantly improve and the actual use of water to extinguish fires will be reduced for the communities that employ effective fire suppression which reduces water consumption records. As a final reminder, the following listing demonstrates the effective uses of water as a percent function for the cooling potential of 1 pound of water: 100 percent of efficiency—1,150 Btu/lb 75 percent of efficiency—863 Btu/lb 50 percent of efficiency—575 Btu/lb 25 percent of efficiency—288 Btu/lb 10 percent of efficiency—115 Btu/lb Recall from above that a straight fire steam, whether from a hand hoseline or a master stream appliance has only about 10 percent of water efficiency. The above numbers clearly indicate the inefficiency of applying water by straight stream method, although this method may be necessary for coping with deepseated fires and for overhauling fires. Water that is not used effectively in fire extinguishment often results in more water damage to the property than the fire itself.
The Latest Methods for Improving Structural Fire Suppression Effectiveness
Two fast-growing developments in structural fire suppression may have a significant impact on water demand needs for specific occupies and for initial fire attack in the near future. First, is the use of water mist technology for special-hazard fire problems and for protecting one- and twofamily homes. Second, is both the introduction of Class A Foams and the technology to apply these foams for the reported dramatic improvement of confining and extinguishing developing structure fires to the room or area of origin. Each of these approaches to improved structural fire suppression is examined separately.