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10 January 2025
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Featured FRI Magazine article: Firefighting nozzles: fog versus solid stream by Colin Deiner
Firefighting nozzles are designed to put out fires by getting the right amount of water, in the right form, to the right place
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Lloyd Layman
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Combination nozzle use requires more training
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Each fire will have particular characteristics that will dictate the best nozzle to use
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There is no ‘one-size-fits-all’ solution
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https://www.frimedia.org/uploads/1/2/2/7/122743954/fri_vol_2_no_12.pdf
This week’s featured Fire and Rescue International magazine article is: Firefighting nozzles: fog versus solid stream written by Colin Deiner, chief director, Disaster Management and Fire Brigade Services, Western Cape Government (FRI Vol 2 no 12). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Firefighting nozzles: fog versus solid stream
By Colin Deiner, chief director, Disaster Management and Fire Brigade Services, Western Cape Government
One of the oldest arguments in firefighting is around the best nozzle to use for structural fire attack; solid stream/smooth bore or fog/combination nozzles. This is not a new argument; it has been going on for more than 150 years. The proponents of the solid stream nozzle argue that they are more effective because they have better reach, are less likely to upset the thermal balance inside the structure and are less likely to cause steam burns to attack teams. They argue that fog/combination nozzles do not generally provide sufficient reach or penetration and can push the fire through to the rest of the building.
In contrast to this you will get the people who prefer the versatility and higher heat absorption of the fog/combination nozzle. They will further argue that with the advent of the automatic nozzle they get a constant water flow, regardless of the amount of supply pressure, therefore making them more reliable.
Their main argument would be that when fire fighters unexpectedly encounter a flammable liquid fire in a structure or a window suddenly blows out, they would need the protection of a combination nozzle.
I will not attempt to settle this argument for-once-and-for-all in this article; it’s been going on for too long. I will, however, offer a few thoughts on what I believe are the best utilisation of both models. I trust this will stimulate further debate.
When reading this article, please note that I am referring to the use of firefighting nozzles during structural fire attack only. I am not considering the wider spectrum of use such as petrochemical or other flammable hazardous materials fires. In these cases, the amount of protection a fire stream has to provide to an attack team would be a prime consideration and there are many people far more qualified to discuss this than me.
Nozzle types
Firefighting nozzles are designed to put out fires by getting the right amount of water, in the right form, to the right place. In order to achieve this, the nozzles must be capable of controlling the flow of the water, get the water to where it’s needed and to create the different water forms required to extinguish the fires.
The velocity created at the end of the waterway converts water pressure into velocity that provides the reach required to get the water (wet stuff) onto the fire (red stuff). Not all fires can be extinguished in the same way. Some fires need to be penetrated by a solid stream while other fires can more effectively be extinguished by the heat adsorption properties of a fog stream.
There are principally two types of nozzles, solid stream/smooth bore or fog/combination nozzles. Various producers of firefighting nozzles will expand this list to other types but essentially it would be variations of the above two.
Solid stream/smooth bore nozzle: Smooth bore nozzles are among some of the oldest types of nozzles used in the fire service. Aside from the shut-off valve, it contains no other parts. These nozzles have a tapered design and unlike other types of nozzles, smooth bore nozzles provide a solid stream of water that is capable of penetrating through flames to directly attack what material is burning.
Fog/combination nozzle: Fog nozzles are capable of producing anything from a wide dispersion pattern to a straight stream of water. Unlike smooth bore nozzles, the introduction of air into the water column decreases penetration and the distance the stream of water can travel. When used in its wide-dispersion setting, it is effective against petrochemical fires because it creates a curtain of water between the fire and the nozzle team. In hydraulic ventilation, the fog pattern pulls air from behind it forward, pushing smoke out of an enclosed space.
Some history
Fire fighters in the early 1990s did not have to make a choice of which nozzle to use as the solid stream/smooth bore was the only one available.
It was in 1950 that someone called Lloyd Layman carried out a series of studies based on United States Coast Guard and Navy tests that proved how the fog pattern had greater heat absorption abilities in sealed compartments with extreme ceiling temperatures. A further requirement for this to work was for the fog stream to be indirectly applied to prevent steam injuries to attack crews.
In 1951 Keith Royer and Floyd W Nelson from Iowa University introduced the combination nozzle into the fire service. This allowed fire suppression teams to use the fog stream to create a thermal balance and absorb the heat before applying water to the seat of the fire.
In the late 1960s Chief CH McMillan of the Gary, Indiana, Fire Task Force, developed the automatic nozzle, also referred to as a pressure regulating or a constant pressure nozzle. The nozzle was developed to solve the problems of using big streams with limited water supplies. The automatic nozzle has led to a number of tactical innovations and provided greater flow deliveries than before.
Advantages and disadvantages
As mentioned earlier, both nozzles have its advantages and disadvantages. The fog/combination nozzle’s greatest advantage is its versatility. The various settings will allow a hose team to commence an immediate rapid fire attack and enable them to enter the structure, hydro-ventilate, cool the structure, protect themselves and any rescue crews and attack the fire with a high possibility of success.
There is a very strong opinion that a solid stream will provide an effective overhead cooling effect and offer effective flashover control. This is supported by the conception that when a fog stream is directed at a ceiling into the thermal layer, it could cause a disruption of the layer and blend the heat and gases causing superheated air and steam throughout the structure.
Recent research has proved that short, one-second bursts of 360 litres per minute fog streams can produce temperature spikes of 150°C (temperatures drop from 600°C to 450°C and then rapidly return to 600°C). With a solid stream the spike is much wider, with the spike being as high as 500°C from a 360 litres per minute stream. This causes the temperature to bounce between 200°C and 700°C. The solid stream will produce the greater cooling effect but in a compartment fire, it poses the threat of excessive amounts of steam and super-heated air down on the nozzle team. To avoid this, greater control of the overhead conditions are required to produce a better cooling gradient.
The cooling effect of the fog nozzle is therefore more controlled and gradually brings control over the atmosphere in contrast to the sudden volume of steam caused by a burst of water from a solid stream nozzle.
The hydraulic-ventilation potential of the fog stream can be effectively employed in a rapid attack scenario where positive pressure or vertical ventilation activities still have to be commenced.
The solid stream nozzle will obviously give you more reach and penetration but is limited in its ability to achieve a thermal balance or hydro-ventilate. By creating a Z-pattern with your solid water stream you should be able to achieve an acceptable level of cooling of the fire compartment.
In a larger volume, ventilated structure solid streams will be very effective. The solid stream leaving the nozzle will upon striking a hard surface break up into larger droplets and still provide an effective cooling and penetration on the fire surface. The argument that a fog stream can always be adjusted to form a straight stream is valid and should be seen as distinct advantage of the combination nozzle. This happens when the combination nozzle is adjusted to a narrow pattern. Reach and penetration is improved in this state. Water leaves the nozzle in millions of smaller droplets mixed with air entrained within the stream. When the stream comes into contact with a hard surface it will break up into smaller droplets that will be absorbed by the heat quicker, making it harder to reach the source of the fire.
Pressure
Proponents of the solid stream nozzle will point to the fact that its main advantage is that it will be effective in a low water pressure environment. The advent of low pressure combination nozzles around the late 1990s has largely addressed this problem and today there are a number of combination nozzles available that can provide close to the same performance as a solid stream nozzle in a low pressure situation.
Tests done by many manufacturers and fire services over the years has shown that at equal flows and pressures, the streams from both smooth-bore and low pressure combination nozzles, look alike, have the same reach and reactions and strike with the same impact force. Both nozzles demonstrated an equal amount of turbulence and showed generally the same droplet size.
This would indicate that the streams should reach the fire in very much the same shape.
Selecting a nozzle
Hopefully we have now got to the point where we do appreciate that there is no ‘one-size-fits-all’ solution. Each fire will have particular characteristics that will dictate the best nozzle to use. How do we make that decision?
The first consideration should be the required flow range. This is determined by the available water, pump capacity, hose lays and distance to the fire. By determining what the maximum achievable flow rate under normal circumstances would be, you will be able to factor in the other variables specific to your fire and arrive at the minimum required flow rate required. Then determine what the maximum flow might be that can be managed by the available manpower.
A very important consideration would then be the different patterns that may be required. Certain newer fog nozzles produce almost as good a straight stream as a solid bore nozzle but do require a higher inlet pressure.
The level of training and experience of your fire crews also plays a vital role in deciding your standard operating procedures (SOPs) for nozzle selection at structural fires. Solid stream nozzles require the least amount of training as the engine pressure depends mainly on the length and size of hose. Combination nozzle use requires more training because different engine pressures will be required for each of the flow settings with different lengths and sizes of hose. The pump operator must be trained to accurately control the engine pressure and flow with different lengths and sizes of hoses and different operating conditions.
A clear analysis of your fire risk, level of training, water pressures and supporting equipment will allow you to form a good idea of the needs of each unit within your arsenal and to what level they will be able to utilise the advantages of the two types available.
Horses for courses
As mentioned earlier we must realise that we have many different tools and no one tool is right for every situation.
A fog stream is best used in a non-ventilated structure whereas a solid stream should be used on fires in ventilated structures. The best chance any trapped fire victims have of survival is if a fire is well vented and the fire gets quickly extinguished. You want to achieve this as rapidly and effectively as possible and must plan your fire attack so that all the correct tools are in the right place to achieve this, whether it is the ventilation, forcible entry, rescue or firefighting kit.
Due to its versatility all crosslays and preconnect hoses should be fitted with fog/combination nozzles. As in forcible entry and ventilation though, you don’t only have one piece of equipment for each of these tasks. Why then should you only have one choice of nozzle? In a fire department I worked in some years ago, we took the decision to acquire a number of smooth bore, hand controlled nozzles that were carried by the attack crew together with the fog/combination nozzles for initial attack. Well trained, experienced fire fighters, together with good communication with their pump operators, allowed a rapid changeover if required and provided the crews with an extra tool in their toolboxes and more attack options.
I stress the importance of experienced attack crews. With a solid stream nozzle there is no chance that an inexperienced nozzle man will have it set on the wrong pattern or flow setting, or have it changed to the wrong pattern by accident. Experienced fire fighters will know to test the nozzles position before entering a structure lest he/she crack it open and either upset an unstable load close by or cause excessive steam production when it is not expected.
Many fire services preload their water tanks with class-A foam and in this case it is necessary to ensure you are using fog/combination nozzles as part of the system.
Conclusion
In the two years that I have been writing technical articles for this magazine, I have not written about a more controversial topic than this one. International fire services blogs overflow with arguments for and against both solid stream/smooth bore and fog/combination nozzles. I will no doubt also have readers disagree with this dissertation and you are most welcome to do so.
My final thoughts on this subject are reflected below (I have already mentioned some of them but here they are again):
• There is no single nozzle solution for all fires.
• Solid stream nozzles will give you the advantage of performance at lower pressures.
• Fog/combination nozzles are versatile and provide higher levels of protection.
• Crosslays and preconnect lines should be fitted with fog/combination nozzles with solid stream nozzles as a second option.
• Poorly ventilated interior fires = fog/combination nozzles. Well ventilated structural fire = solid stream/smooth bore nozzles.
This week’s featured Fire and Rescue International magazine article is: Firefighting nozzles: fog versus solid stream written by Colin Deiner, chief director, Disaster Management and Fire Brigade Services, Western Cape Government (FRI Vol 2 no 12). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Firefighting nozzles: fog versus solid stream
By Colin Deiner, chief director, Disaster Management and Fire Brigade Services, Western Cape Government
One of the oldest arguments in firefighting is around the best nozzle to use for structural fire attack; solid stream/smooth bore or fog/combination nozzles. This is not a new argument; it has been going on for more than 150 years. The proponents of the solid stream nozzle argue that they are more effective because they have better reach, are less likely to upset the thermal balance inside the structure and are less likely to cause steam burns to attack teams. They argue that fog/combination nozzles do not generally provide sufficient reach or penetration and can push the fire through to the rest of the building.
In contrast to this you will get the people who prefer the versatility and higher heat absorption of the fog/combination nozzle. They will further argue that with the advent of the automatic nozzle they get a constant water flow, regardless of the amount of supply pressure, therefore making them more reliable.
Their main argument would be that when fire fighters unexpectedly encounter a flammable liquid fire in a structure or a window suddenly blows out, they would need the protection of a combination nozzle.
I will not attempt to settle this argument for-once-and-for-all in this article; it’s been going on for too long. I will, however, offer a few thoughts on what I believe are the best utilisation of both models. I trust this will stimulate further debate.
When reading this article, please note that I am referring to the use of firefighting nozzles during structural fire attack only. I am not considering the wider spectrum of use such as petrochemical or other flammable hazardous materials fires. In these cases, the amount of protection a fire stream has to provide to an attack team would be a prime consideration and there are many people far more qualified to discuss this than me.
Nozzle types
Firefighting nozzles are designed to put out fires by getting the right amount of water, in the right form, to the right place. In order to achieve this, the nozzles must be capable of controlling the flow of the water, get the water to where it’s needed and to create the different water forms required to extinguish the fires.
The velocity created at the end of the waterway converts water pressure into velocity that provides the reach required to get the water (wet stuff) onto the fire (red stuff). Not all fires can be extinguished in the same way. Some fires need to be penetrated by a solid stream while other fires can more effectively be extinguished by the heat adsorption properties of a fog stream.
There are principally two types of nozzles, solid stream/smooth bore or fog/combination nozzles. Various producers of firefighting nozzles will expand this list to other types but essentially it would be variations of the above two.
Solid stream/smooth bore nozzle: Smooth bore nozzles are among some of the oldest types of nozzles used in the fire service. Aside from the shut-off valve, it contains no other parts. These nozzles have a tapered design and unlike other types of nozzles, smooth bore nozzles provide a solid stream of water that is capable of penetrating through flames to directly attack what material is burning.
Fog/combination nozzle: Fog nozzles are capable of producing anything from a wide dispersion pattern to a straight stream of water. Unlike smooth bore nozzles, the introduction of air into the water column decreases penetration and the distance the stream of water can travel. When used in its wide-dispersion setting, it is effective against petrochemical fires because it creates a curtain of water between the fire and the nozzle team. In hydraulic ventilation, the fog pattern pulls air from behind it forward, pushing smoke out of an enclosed space.
Some history
Fire fighters in the early 1990s did not have to make a choice of which nozzle to use as the solid stream/smooth bore was the only one available.
It was in 1950 that someone called Lloyd Layman carried out a series of studies based on United States Coast Guard and Navy tests that proved how the fog pattern had greater heat absorption abilities in sealed compartments with extreme ceiling temperatures. A further requirement for this to work was for the fog stream to be indirectly applied to prevent steam injuries to attack crews.
In 1951 Keith Royer and Floyd W Nelson from Iowa University introduced the combination nozzle into the fire service. This allowed fire suppression teams to use the fog stream to create a thermal balance and absorb the heat before applying water to the seat of the fire.
In the late 1960s Chief CH McMillan of the Gary, Indiana, Fire Task Force, developed the automatic nozzle, also referred to as a pressure regulating or a constant pressure nozzle. The nozzle was developed to solve the problems of using big streams with limited water supplies. The automatic nozzle has led to a number of tactical innovations and provided greater flow deliveries than before.
Advantages and disadvantages
As mentioned earlier, both nozzles have its advantages and disadvantages. The fog/combination nozzle’s greatest advantage is its versatility. The various settings will allow a hose team to commence an immediate rapid fire attack and enable them to enter the structure, hydro-ventilate, cool the structure, protect themselves and any rescue crews and attack the fire with a high possibility of success.
There is a very strong opinion that a solid stream will provide an effective overhead cooling effect and offer effective flashover control. This is supported by the conception that when a fog stream is directed at a ceiling into the thermal layer, it could cause a disruption of the layer and blend the heat and gases causing superheated air and steam throughout the structure.
Recent research has proved that short, one-second bursts of 360 litres per minute fog streams can produce temperature spikes of 150°C (temperatures drop from 600°C to 450°C and then rapidly return to 600°C). With a solid stream the spike is much wider, with the spike being as high as 500°C from a 360 litres per minute stream. This causes the temperature to bounce between 200°C and 700°C. The solid stream will produce the greater cooling effect but in a compartment fire, it poses the threat of excessive amounts of steam and super-heated air down on the nozzle team. To avoid this, greater control of the overhead conditions are required to produce a better cooling gradient.
The cooling effect of the fog nozzle is therefore more controlled and gradually brings control over the atmosphere in contrast to the sudden volume of steam caused by a burst of water from a solid stream nozzle.
The hydraulic-ventilation potential of the fog stream can be effectively employed in a rapid attack scenario where positive pressure or vertical ventilation activities still have to be commenced.
The solid stream nozzle will obviously give you more reach and penetration but is limited in its ability to achieve a thermal balance or hydro-ventilate. By creating a Z-pattern with your solid water stream you should be able to achieve an acceptable level of cooling of the fire compartment.
In a larger volume, ventilated structure solid streams will be very effective. The solid stream leaving the nozzle will upon striking a hard surface break up into larger droplets and still provide an effective cooling and penetration on the fire surface. The argument that a fog stream can always be adjusted to form a straight stream is valid and should be seen as distinct advantage of the combination nozzle. This happens when the combination nozzle is adjusted to a narrow pattern. Reach and penetration is improved in this state. Water leaves the nozzle in millions of smaller droplets mixed with air entrained within the stream. When the stream comes into contact with a hard surface it will break up into smaller droplets that will be absorbed by the heat quicker, making it harder to reach the source of the fire.
Pressure
Proponents of the solid stream nozzle will point to the fact that its main advantage is that it will be effective in a low water pressure environment. The advent of low pressure combination nozzles around the late 1990s has largely addressed this problem and today there are a number of combination nozzles available that can provide close to the same performance as a solid stream nozzle in a low pressure situation.
Tests done by many manufacturers and fire services over the years has shown that at equal flows and pressures, the streams from both smooth-bore and low pressure combination nozzles, look alike, have the same reach and reactions and strike with the same impact force. Both nozzles demonstrated an equal amount of turbulence and showed generally the same droplet size.
This would indicate that the streams should reach the fire in very much the same shape.
Selecting a nozzle
Hopefully we have now got to the point where we do appreciate that there is no ‘one-size-fits-all’ solution. Each fire will have particular characteristics that will dictate the best nozzle to use. How do we make that decision?
The first consideration should be the required flow range. This is determined by the available water, pump capacity, hose lays and distance to the fire. By determining what the maximum achievable flow rate under normal circumstances would be, you will be able to factor in the other variables specific to your fire and arrive at the minimum required flow rate required. Then determine what the maximum flow might be that can be managed by the available manpower.
A very important consideration would then be the different patterns that may be required. Certain newer fog nozzles produce almost as good a straight stream as a solid bore nozzle but do require a higher inlet pressure.
The level of training and experience of your fire crews also plays a vital role in deciding your standard operating procedures (SOPs) for nozzle selection at structural fires. Solid stream nozzles require the least amount of training as the engine pressure depends mainly on the length and size of hose. Combination nozzle use requires more training because different engine pressures will be required for each of the flow settings with different lengths and sizes of hose. The pump operator must be trained to accurately control the engine pressure and flow with different lengths and sizes of hoses and different operating conditions.
A clear analysis of your fire risk, level of training, water pressures and supporting equipment will allow you to form a good idea of the needs of each unit within your arsenal and to what level they will be able to utilise the advantages of the two types available.
Horses for courses
As mentioned earlier we must realise that we have many different tools and no one tool is right for every situation.
A fog stream is best used in a non-ventilated structure whereas a solid stream should be used on fires in ventilated structures. The best chance any trapped fire victims have of survival is if a fire is well vented and the fire gets quickly extinguished. You want to achieve this as rapidly and effectively as possible and must plan your fire attack so that all the correct tools are in the right place to achieve this, whether it is the ventilation, forcible entry, rescue or firefighting kit.
Due to its versatility all crosslays and preconnect hoses should be fitted with fog/combination nozzles. As in forcible entry and ventilation though, you don’t only have one piece of equipment for each of these tasks. Why then should you only have one choice of nozzle? In a fire department I worked in some years ago, we took the decision to acquire a number of smooth bore, hand controlled nozzles that were carried by the attack crew together with the fog/combination nozzles for initial attack. Well trained, experienced fire fighters, together with good communication with their pump operators, allowed a rapid changeover if required and provided the crews with an extra tool in their toolboxes and more attack options.
I stress the importance of experienced attack crews. With a solid stream nozzle there is no chance that an inexperienced nozzle man will have it set on the wrong pattern or flow setting, or have it changed to the wrong pattern by accident. Experienced fire fighters will know to test the nozzles position before entering a structure lest he/she crack it open and either upset an unstable load close by or cause excessive steam production when it is not expected.
Many fire services preload their water tanks with class-A foam and in this case it is necessary to ensure you are using fog/combination nozzles as part of the system.
Conclusion
In the two years that I have been writing technical articles for this magazine, I have not written about a more controversial topic than this one. International fire services blogs overflow with arguments for and against both solid stream/smooth bore and fog/combination nozzles. I will no doubt also have readers disagree with this dissertation and you are most welcome to do so.
My final thoughts on this subject are reflected below (I have already mentioned some of them but here they are again):
• There is no single nozzle solution for all fires.
• Solid stream nozzles will give you the advantage of performance at lower pressures.
• Fog/combination nozzles are versatile and provide higher levels of protection.
• Crosslays and preconnect lines should be fitted with fog/combination nozzles with solid stream nozzles as a second option.
• Poorly ventilated interior fires = fog/combination nozzles. Well ventilated structural fire = solid stream/smooth bore nozzles.