Cobra is a versatile firefighting tool designed to address key operational challenges such as fire gas cooling, hidden fires, heat shielding, and complex fires. It can be installed in a variety of vehicles to meet each organization’s needs, whether as a stand-alone unit for rapid deployment in narrow streets or rural areas, or as a built-in system on a full-sized fire engine.
Even though the system comes in different configurations, the most prominent difference for firefighters’ operations would be the water flow rate.
When using cutting extinguishers for fire gas cooling in fire compartments, both flow rate and system adaptability are key. Cobra offers two systems delivering 30 respectively 60 litres of water per minute (lpm), equivalent to 8 and 16 US gallons per minute (gpm), respectively.
The actual flow rate differs, ranging from 28-32 lpm and 58-62 lpm, depending on the actual engine performance. For sake of simplicity, we round the figures to 30 lpm (8 gpm) respectively 60 lpm (16 gpm).
Piercing Performance vs. Cooling
Although higher water flow rates can increase cutting power in certain system types, Cobra is engineered for effective performance and operational reliability rather than maximum energy output. (1) The smaller system, with a narrower nozzle, achieves a slightly faster piercing time, but such seconds differences have limited tactical significance, compared to one of the main objectives: cooling hot fire gases efficiently from a safer position outside the structure while creating safer interior conditions.
To compare the performance of fire gas cooling between the two systems, tests have been carried out. A fire compartment, 40-foot container, was pre-heated to approximately 600°C (1112°F), and the time to cool the compartment to 70°C (158°F) was measured. Each system was tested twice.
The results are shown in the diagram below and show that the 60 lpm system reduced the temperature faster than the 30 lpm system.
The results suggest that both systems can cool fire gases effectively, although the higher flow rate of the 60 lpm unit resulted in approximately half the cooling time compared to the 30 lpm system.
Fire Suppression Efficiency
While fire gas cooling is one objective, Cobra is a versatile tool and delivers competence to more scenarios, such as hidden fires inside constructions and, more recently the awarded method of piercing lithium-ion battery casings, heat shielding between two objects and complex fires where multiple tools and technique are combined to enhance extinguishing capability. (2) (3)
In all the above scenarios, flow rate alone is not the deal breaker. Even though the 60 lpm system delivers twice as much water, the droplet characteristics and distribution pattern are often more critical. However, in the case of hidden fires, the flow velocity plays an additional role by allowing the jet to pierce into voids and cavities, improving the system’s ability to reach concealed fires.
The efficiency of the water mist lies in its ability to absorb heat. The ideal droplet size maximizes surface area, which enhances heat absorption. This effect is particularly relevant for fire gas cooling. Research conducted by the Research Institute of Sweden (RISE) found Cobra’s droplets to be significantly smaller, approximately 170 µm, compared to over 900 µm for other systems. (4)
The smaller the droplets, the larger the combined surface area, and the more heat they absorb.
Theory
One litre of water requires approximately 2.3 MJ to evaporate. Hence, 60 litres of water times 2.3 MJ means that 60 lpm can absorb around 135.6 MJ per minute. The heat release rate (HRR) of a fire is measured in MW, since 1 MW equals 1 MJ/s, 135.6 divided by 60 is the output of 2.26 MW that, in theory, can be absorbed per minute. (2)
In other words, if all the 60 litres of water delivered per minute were to evaporate, the theoretical heat absorption capacity of the Cobra system would be approximately 2.3 megawatts (MW). This means that, under ideal conditions, the system could absorb heat energy at a rate comparable to the peak heat release rate (pHRR) of a fully developed room fire. Studies of furnished compartment fires conducted in standard ISO 9705 test rooms (approximately 3.6 × 2.4 × 2.4 m and furnished as typical living rooms with a sofa, table, television, rug, and curtains) show that flashover typically occurs around 1 MW, with peak HRR values reach 2.5–3.3 MW. Cobra’s potential cooling capacity thus falls within the same order of magnitude as the maximum heat output of such a room fire. (5) (6)
A system delivering half the flow, 30 lpm, would therefore, in theory, absorb roughly half the amount of heat. In larger fires where peak HRR values greatly exceed 3 MW, this can be compensated for by using multiple Cobra systems simultaneously, each contributing its share of cooling and suppression capacity.
Keep in mind, that in practice, not all of the water evaporates. Some of the energy goes into heating the droplets to boiling point, and some water reaches cooler surfaces before it can vaporise. However, due to the fine droplet size, a relatively high proportion of the water does evaporate where it matters, in the hot gas layer. This makes Cobra highly effective at reducing temperatures and radiation heat inside compartments.
Technical Differences
Although both Cobra systems operate at the same pressure of 300 bar (4,351 psi), the difference in water flow means that the larger system requires more power to drive the pump and maintain performance. The 30 lpm system operates at approximately 30 horsepower, while the 60 lpm version needs around 60 horsepower. A simple rule of thumb is that roughly one horsepower is required per litre of water per minute at 300 bar.
The nozzle diameter also differs slightly between the configurations, 1.6 mm for the 30 lpm system and 2.3 mm for the 60 lpm version. These are optimised for cutting performance, water speed and durability, ensuring both systems deliver the same fine mist quality and piercing capability.
Summary
Choosing between the 30 (8 gpm) and 60 lpm (16 gpm) Cobra systems depend on the operational context, including the specific risk profile and tactical objectives of each fire service organisation. It is important to consider what outcomes Cobra is intended to achieve and in which types of scenarios the method will be applied.
Both systems deliver high-pressure, fine-droplet water that rapidly reduces heat, improves visibility and lowers the risk of flashover, allowing firefighters to operate more safely and efficiently. By reducing exposure to toxic gases and extreme heat, Cobra not only enhances tactical capability but also contributes to long-term firefighter health and safety.
The choice between the two systems is not about which is better, but about matching capacity to context. Ultimately, successful Cobra use relies not only on the equipment itself, but on how well it is integrated into local tactics and training. With the right understanding and implementation, either system becomes a powerful tool for safer, cleaner and more efficient firefighting.
Source
- Huang, Zhongwei, o.a. Abrasive Water Jet Perforation and Multi-Stage Fracturing. u.o. : Gulf Professional Publishing, 2018. s. 68.
- Gsell, Julien. Assessment of Fire Suppression Capabilities of Water Mist – Fighting Compartment Fires with the Cutting Extinguisher. Faculty of Art, Design and the Built Environment. Coleraine (F) : University of Ulster, 2010.
- Johansson, Anton. Measurement of radiation absorption in the spray from the Cobra cutting extinguisher. Institutionen för samhällsbyggnad och naturresurser. Luleå : Luleå Tekniksa Universitet, 2018.
- SP Technical Research Institute of Sweden. Spray Characterization of the Cutting Extinguisher. Fie Research. Borås : SP Technical Research Institute of Sweden, 2012.
- Comparative Room Burn Study of Furnished Rooms from the United Kingdom, France and the United States. Blais, M.S., Carpenter, K. & Fernandez, K. u.o. : Springer Nature Link, March 2020, Fire Technology, Vol. 56, ss. 489-514.
- Karlsson, Björn och Quintiere, James G. Enclosure Fire Dynamics. Florida : CRC Press LCC, 2000. s. 26.
