BY BRUCE LAKE
A dragon is a legendary creature that spews fire. Battle tales about this beast have been passed down from generation to generation inside every fire station. For example, some dragon slayers claim they need only 100 gallons of water to drown a dragon while others need 500. Why do some firefighters need less water than others? The answer is simple: It takes knowledge and skill to put water in the right place the right way. Fire suppression is not about the type of nozzle you hold; it’s about what you do with the water that comes out of the nozzle. In golf, some players blame a poor shot on the club. The truth is that technique has a greater impact on outcomes than fancy equipment. This article details the fundamentals of extinguishment. During structural firefighting, water is released for one of three reasons: fire extinguishment, safer movement, or defensive operations.
Fire Extinguishment
The fuel most commonly encountered during firefighting operations is solid fuels. Common examples include structural components and building contents. A fire will present itself in two forms—flaming and smoldering combustion. Flaming combustion occurs when fuel vapor ignites after being released from a solid by the application of heat through a process called pyrolysis. Smoldering combustion occurs when the surface of a solid burns without flame. In other words, the surface of any solid material is the fuel tank of the fire. The quicker the fuel supply can be shut off, the faster the fire will go out. If water is not applied directly to the burning surface, the fire cannot be extinguished.
Direct Attack
A direct attack is typically used during offensive operations to stop combustion within a room or a building. Water is applied directly to the burning surface using a straight stream (fog nozzle) or a solid stream (smooth bore nozzle). These water streams are the best choices for a direct attack. Their mass and smaller surface area maximize the amount of water that reaches the burning surface while minimizing water lost to evaporation.
The intent of a direct attack is twofold: first, to cool the burning surface to stop pyrolysis; second, to remove the heat energy required for combustion to occur. According to the 19th edition of the Fire Protection Handbook, the pyrolysis of wood begins at temperatures below 392°F/200°C. Water will absorb heat energy in the following three ways:
- Specific heat of water. Heat energy is absorbed every time water temperature is raised by one degree. This energy transfer stops once water reaches a temperature of 212°F/100°C.
- Latent heat of vaporization. More heat energy is absorbed when water transforms from a liquid into a vapor. This change in state of matter absorbs more heat energy than the entire specific heat of water. The transformation occurs at 212°F/100°C.
- Specific heat of steam. Once steam has been formed at 212°F/100°C, it will also absorb a tremendous amount of heat energy. Concerns about using steam are discussed later.
Direct Attack Techniques
Aggressively applying water directly to a burning surface is the best way to stop flaming and smoldering combustion. Hose teams should always apply water as soon as a burning surface comes within range. Water flowing away from a target indicates that the surface has been cooled and that the heat energy has been removed. You are wasting a precious resource and stressing the structural load when water returns to sender. Don’t waste water: Find a new target or stop flowing. The two effective direct attack water application techniques are penciling and painting.
Penciling
Penciling is used on small fires. Aim the nozzle at the burning fuel surface and open and close the nozzle bail so a single pencil of water (the length of the distance from the nozzle to the target) hits the burning fuel surface. Hitting a small fire with a single shot of water minimizes steam production, prevents excessive water application, and allows the nozzle firefighter to quickly identify fire flare-ups or a successful knockdown. The fire is considered knocked down when it stops growing and most of the flaming combustion has been eliminated. More than one shot may be needed to knock down a fire. During overhaul, coat any remaining flaming or smoldering surfaces with water. If the fire is bigger or if multiple surfaces are burning, a painting technique may be more appropriate.
Painting
The painting technique consists of aiming the nozzle at one end of the large burning surface or surfaces; opening the nozzle bail; and sweeping the water stream across all burning surfaces, like a painter’s brush, before closing the bail. You may have to repeat this process several times, or you may have to use the penciling technique to finish knocking down the fire. Once again, this technique minimizes steam production, prevents excessive water application, and maintains visibility, which allows the nozzle firefighter to quickly determine if the actions are working.
Using other water application techniques during a direct attack may produce negative results. For example, using a narrow or a wide fog pattern will entrain a large volume of air, which will push products of combustion. Steam may also be created if temperatures are 212°F/100°C or higher. The movement of steam or products of combustion could potentially harm unprotected civilians and firefighters. An entrainment of air may also increase the fire’s heat release rate. Studies by the National Institute of Standards and Technology (NIST) and Underwriters Laboratories (UL) have documented that whipping a solid or a straight stream in a circle will entrain the same amount of air as a positive pressure fan. This whipping technique pushes smoke in the same way as a fog stream. Whipping a solid or a straight stream off the walls and ceiling will create steam if temperatures are hot enough. Ventilation and the fire attack must be coordinated when pushing products of combustion with a fog stream or using a whipping action. Avoid recklessly opening the nozzle bail (fog or solid) and letting the water flow freely with no target or intent. This amateur application of water may create steam, reduce visibility, lower the hot smoke layer, and waste water.
Indirect Attack and Combination Attack
It is difficult to think of two other terms or techniques in the fire service that have been as misinterpreted, poorly taught, and inappropriately applied and have caused as much grief as the indirect and combination attacks. Simply put, the intent of both attack methods is to knock down a fire with steam.
Lloyd Layman, the pioneer of the indirect attack, discovered that steam is a very effective fire extinguishing agent. Steam absorbs a tremendous amount of heat energy quickly. When steam expands, it also pushes air out of a compartment, decreasing oxygen levels. According to the 2014 edition of National Fire Protection Association 921, Guide for Fire and Explosion Investigations, under standard temperature and pressure conditions, oxygen levels below 15 percent by volume will not support combustion. It is commonly known that steam will expand its volume 1,700 times at 212°F /100°C. What is not as well known is that steam will expand its volume approximately 2,600 times at 572°F/300°C and approximately 3,900 times at 1,112°F/600°C (flashover temperature).
Keith Royer and Floyd W. (Bill) Nelson improved Layman’s steam production technique with the development of the combination attack. Instead of keeping the fog stream in a fixed position aimed at the smoke, Royer and Nelson discovered that steam production could be maximized by rolling a fog stream around the room so that the water contacts the walls and ceiling. In my opinion, since the intent of both the indirect and combination attack is the same, they both should be referred to as a steam attack.
Steam Attack Technique
Large droplets of water are ideal for a direct attack: minimal evaporation, maximum cooling of burning surfaces. Tiny droplets of water are best for a steam attack: maximum vaporization, maximum heat absorbed. Deflecting a solid or a straight steam off the ceiling and walls will create steam; however, the large droplets produced are very inefficient at absorbing heat energy. A fog nozzle creates much smaller droplets than a smooth bore nozzle. Steam is most effectively created using a narrow fog pattern. Spray the fog stream in a circular pattern directed at the top half of the room, moving from wall to ceiling to wall and then back through the smoke layer. You can also use the “T” and “Z” patterns commonly described in modern textbooks.
Many firefighters hesitate to use steam. This reluctance can be traced back to horror stories passed down from the previous generation. Fears of steam burns and dropping the hot smoke layer are common concerns. Today, with modern protective equipment, steam injuries are usually the result of exposed skin; more serious events are caused by firefighters getting caught in a hot gas flow path. Why are so many people in the fire service afraid of steam? Many fire service personnel don’t understand that attempting to extinguish a fire with steam should be conducted only under the following very specific conditions:
- The fire compartment is fully involved or backdraft conditions are suspected.
- There is no survivability profile within the compartment.
- Protection is available for the nozzle team, such as a door to close or a vent opening to push steam out. Heat travels from hot to cold and from high pressure to low pressure. Firefighters injured by steam are typically the coldest thing in the low-pressure outlet. Always conduct a steam attack from outside the fire compartment and from a safe position.
- To complete extinguishment, direct attack and overhaul must immediately follow a steam knockdown.
Safer Movement
Gas cooling, door entry cooling, and exterior water application are not extinguishment techniques. These water applications are typically employed when the location of the fire is undetermined or shielded. The intent of these methods is to make movement within the hazard zone safer. Conditions are improved by reducing the thermal threat and by delaying the activation of rapid fire events such as flashover, backdraft, and autoignition. It cannot be overstated that a hose crew must put water on burning surfaces at the earliest opportunity.
Gas Cooling (Pulsing)
Gas cooling, sometimes referred to as pulsing, was developed in Sweden. Its intent is to control the environment when the fire can’t be attacked directly. This method works by cooling hot gases below their autoignition temperature. When gas cooling is applied correctly, smoke contracts (improves visibility), temperatures lower (reduces thermal threat), the hot smoke layer doesn’t drop (prevents injury), and rapid fire events are delayed (increases safety).
Swedish research has determined that the ideal water droplet size for gas cooling is 0.3mm. If the droplet is bigger, it will punch through the hot gases and contact the walls or ceiling, producing steam and lowering the hot gas layer. This result is highly probable when using a solid or a straight stream for gas cooling. If the droplet is too small, it will evaporate before it reaches the hot gases. An adjustable-gallonage fog nozzle with 100 pounds per square inch nozzle pressure set at 30 gallons per minute is ideal for creating effective droplets at a typical residential room-and-contents fire. You will have to dial up the gallonage for a direct attack. In large commercial or industrial structures with high ceilings, the droplets may not be able to reach the ceiling. In this situation, the only option for gas cooling is to deflect a straight or solid stream off the ceiling.
Gas Cooling Technique. The gas cooling stream consists of a narrow fog mist, produced by quickly opening and closing the fog nozzle bail. So, how does a firefighter determine the correct droplet size? When the fog mist hangs in the air for three to four seconds, the droplet size is good. If the droplets fall directly to the ground, they are too big and heavy. If the mist is carried away by the wind, the droplets are too small and light. Practice this technique on the drill ground before applying it in the field. Fire conditions and room geometry will dictate the duration and frequency of gas cooling.
For example, a big room with a low interface layer and flames rolling across the ceiling will necessitate longer, more frequent pulses than a smaller room with a high interface layer and light smoke. Adjust the fog mist width and length for the size of each room. The key application point is to maximize mist contact with smoke and minimize mist contact with walls and ceiling. The travel distance of the droplets can be lengthened in three ways: hold the bail open longer, narrow the fog pattern, or increase the flow rate.
Signs that your gas cooling is working include improved visibility; cooler temperatures; and the sight, sound, and feel of water droplets falling. Excessive water contact with a hot ceiling or walls will create steam and drop the hot smoke layer. It takes continuous practice to master this skill.
Door Entry Cooling
Gas cooling should be a part of door entry procedures. This method is used when smoke is visible around a door. The intent is to lower the temperature of smoke below its autoignition temperature and cool the surface of the door. This procedure reduces the chances of smoke autoigniting when the door is opened and possibly igniting fuel inside the structure. Pulse water across the top of a closed door. If steam appears on the door, there are likely hazardous conditions waiting on the other side. Beware, an insulated door may not give any indication of the fire conditions behind it.
Exterior Water Application
Blitz attack, transitional attack, hit it hard from the yard, and reset the fire are all terms for the same thing, exterior water application. The main objective of every engine company is to get water on the fire as fast as possible. Circumstances will determine whether using an exterior water application or taking the hoseline immediately inside is more appropriate. NIST and UL studies have shown that exterior water application reduces the thermal threat for firefighters and victims. It also delays the activation of rapid fire events such as flashover and backdraft. If water can be put on the fire while you are approaching the building or while you are waiting for personnel to mask up, do it! Studies have documented that the products of combustion are not pushed into the building if water is applied from the exterior with good technique.
Exterior Water Application Technique. Exterior water application can happen in two ways. First, conduct a direct attack if you can see the burning fuel surface. Second, if you can’t see the burning surface, direct a straight or a solid stream on a steep angle through a window or an opening to deflect water off the ceiling. This produces a sprinkler effect within the compartment. Apply water for 10 to 30 seconds. The ideal path and target of the steep angle flow are through the inlet side of a bidirectional flow, aiming for the center of the ceiling. This prevents any blockage of the outlet flow and maximizes the distribution of water throughout the compartment. Never use a fog pattern or whip a solid or a straight stream in a circle during exterior water application. The air current created will push products of combustion back into the structure. You must still go inside the structure and extinguish the fire with a direct attack.
Defensive Operations
During defensive operations such as a fire through the roof or a fully involved structure, collapse zones, protection from radiant heat, and big water are significant safety and operational concerns. Good surround-and-drown procedures plus exposure protection are vital to successful and safe defensive operations.
Surround and Drown
Surround-and-drown operations are typically not very efficient when it comes to water application and fire extinguishment. For example, a steam attack is not practical because it will necessitate that personnel operate inside the collapse zone and will also expose firefighters to radiant heat. The direct attack is generally ineffective because water can’t be applied directly to burning surfaces. During surround-and-drown operations, apply big water with straight or solid streams. These streams have the longest reach and best penetration when pumped correctly. Long-range water application protects personnel from radiant heat and building collapse.
Exposure Protection
Heat energy is transferred to exposures by direct flame contact and radiant heat. This energy transfer releases fuel vapor from the exposure and may cause flaming or smolder combustion. The best way to prevent this from happening is to cool surfaces with a straight or a solid water stream. A water curtain is not effective because it absorbs only a tiny amount of heat energy.
Fireground operations are dynamic. Good firefighters can recognize changing conditions and quickly adjust their hose stream to deal with new threats. Every firefighter must master a variety of water application techniques such as penciling, painting, steam attack, gas cooling, and exterior water application. Fire suppression is not about the nozzle you hold; it’s about what you do with the water that comes out of the nozzle. If you understand how a tool works, you can use any variation of that tool. The fire will react based on where and how you apply the water. You must become more proficient in water application. On the street, that translates into faster extinguishment, less water damage, and fewer firefighter injuries and fatalities. Knowledge increases efficiency; practice refines skills. Don’t get burned; drown the dragon!
Bruce Lake is a career captain with Halifax Regional Fire and Emergency in Nova Scotia, Canada. He is an accredited level 4 fire officer, level 3 fire service instructor, level 2 firefighter, and safety officer. He is a graduate of the fire service management program at Dalhousie University. He is a Blue Card incident command instructor and has also been certified by the International Society of Fire Service Instructors to instruct in modern fire behavior and SLICE-RS. He was a curriculum contributor to the Canadian fire dynamics project From Knowledge to Practice. Prior to joining the fire service, he was an infantry officer in the Canadian Army.
