Fire Control and Suppression by Water-Mist Systems

PurposeThe water mist fire suppression system (WMFSS) is an environmentally friendly fire protection system, replacing the total flooding halon system. It is starting to be popular in Hong Kong with five systems approved. However, such systems were tested under some scenarios very different from real fires. Performance under practical scenarios should be evaluated thoroughly. Full‐scale burning tests should be carried out to support that the systems would work in real fire scenarios as expected. This paper aims to briefly discuss whether the water mist system is suitable for use in Hong Kong.Design/methodology/approachFive water mist systems were approved in Hong Kong based on the fire test certificate provided by the manufacturers. Four systems were selected in this paper for discussion. Conditions of the fire scenarios in which the approved systems would work are described. The test scenario encountered should match with real fires. Such systems would work satisfactorily in the application area proposed. They are good for enclosed rooms such as machinery spaces and plant rooms. But applying such systems for use in retail areas or libraries should be watched carefully, particularly those with high ventilation rates.FindingsIt is observed that the four approved systems were only evaluated on machinery plant rooms with volume less than 500 m3. They are demonstrated to be effective in extinguishing a wide range of bigger Class B fires with very little residual water in a short time. However, the loss of water vapor under mechanical ventilation conditions might reduce the extinguishing capability of mist. The water mist nozzle should not be installed near to the exhaust and supply positions of the mechanical ventilation system. Note that WMFSS is not effective in handling shielded fires due to the lower mist concentration.Practical implicationsFull‐scale burning tests on pool fires of different shapes under water mist were carried out. It was demonstrated that WMFSS might not work under some fire scenarios. Different scenarios on the amount and arrangement of combustibles, room geometry and sizes would affect the system performance. Further, shop fires were burnt with performance of the water mist system evaluated. Heat release rate curves on the shop fire with and without discharging water mist are measured. Reignition occurred once water supply was shut down, burning up all combustibles.Originality/valueEffectiveness of WMFSS is determined by other factors, including the spray characteristics, fire size, ceiling height and ventilation rate in the compartment. Their performance in mechanical ventilation rooms should be watched. As a result, the total flooding system might not be so good. Localized water mist systems directed to the hazard might be more reliable to suppress fire. Water nozzle design is a key area as raised by the principal author. Anyway, the possible fire scenarios must be identified in designing workable WMFSS. Full‐scale burning tests should be conducted to demonstrate the system performance.

Firefighting systems for electrical cables are crucial for safety and functionality during emergencies. They ensure the continuity of critical safety systems, minimize fire spread, and reduce the risk of smoke and toxic gas exposure. Therefore, the objective of the current work is to experimentally investigate the performance and effectiveness of a water mist firefighting system for protecting electrical cables, contributing to the design and development of water mist nozzles. Three types of cables, namely navigation cable, power cable, and electrical cable, were used to investigate the fire protection performance of two different fire nozzles: the Viking nozzle and the ES nozzle. The experiments were conducted in the Firefighting Laboratory of the Mechanical Power Department, Faculty of Engineering (El-Mataria), Helwan University, using a low-pressure water mist system to extinguish cable fires. The experimental comparison between the water mist nozzles was based on visual observation, temperature, fire extinction time, working pressure and water flow rate. The results of this experiment showed that low pressure water mist system is very effective for small-scale cable fires. Moreover, the Viking nozzle achieved superior performance by reducing the fire suppression period by around 76%, 55% and 25% for power cables, electrical cables, and navigation cables, respectively, and shortening the cooling period by about 82 - 83% compared with the ES nozzle.

Electricity is an important energy supply for industry, and long‐distance transmission in China mainly relies on cable tunnels, while cable tunnel fires occur frequently. A 1:1 scale tunnel model with a length of 20 m, a width of 2.5 m, and a height of 2.5 m was used to conduct experimental research on the temperature field of the ceiling of a high‐voltage fine water mist suppression cable tunnel. The article conducted experimental research on parameters, such as nozzle pressure, nozzle position, and longitudinal ventilation speed in high‐pressure water mist systems using n‐hexane as the ignition source. The results indicate that the high‐pressure water mist system can effectively reduce the ceiling temperature during cable tunnel fires. When the mechanical smoke evacuation system is activated, it leads to a reduction in the overall temperature within the tunnel. When the mechanical smoke extraction system is integrated with the high‐pressure water mist system, therefore, it is feasible to integrate the high‐pressure water mist system with the mechanical smoke exhaust system in engineering applications.

The objective of this work is to investigate the diesel analog pool fire with water mist .For this purpose, a series of water mist fire suppression experiment are carried out by changing the nozzle operating pressure, the source of fire power, opening and closing the exhaust fan to analyze the inhibitory effect of water mist to oil pool fire in the enclosed compartment of 5.0m × 5.0m × 3.0m. The results shows that extinguishing efficiency first increases and then decreases when the nozzle operating pressure increases from 8MPa to 12MPa, reaching the highest efficiency at 10MPa; increasing the power of the source of fire, the burning speed increases and the water mist fire extinguishing efficiency decreases; fresh oxygen coming in when smoke exhaust fan is turned on and water mist fire suppression efficiency decreases. Using FDS to simulate the water mist extinguishing oil pool fire, the predict temperature field and extinguishing time are basically consistent with the experimental results. In the actual applications of water mist fire suppression systems engineering, we can use the FDS field simulation methods to predict the characteristic parameters variation of the fire fighting fire temperature and component concentration, which is significant to the fire extinguishing system optimized design.

To optimize the design of a water mist fire suppression system or to provide input data and validation data for field models, the characteristics of the water mist field are needed. This data typically consists of the distribution of droplet sizes and velocities. In this research a LS2000 Laser Sizer has been proposed to simultaneously determine spray characteristics of 408 kinds of self‐developed nozzles for fire suppression. The results of LS2000 Laser Sizer measurements to characterize the water mist produced by nozzles for suppressing pool fire are presented. These data can provide a foundation to the design and optimization of additive‐containing WMFSS. To explore the effect of the water pressure on the droplet size distribution and spray velocity, data from three typical pressures of 0.9MPa, 1.2MPa and 1.5MPa have been obtained. With the measured average size and distribution of droplets, a comparison between three nozzles was made in the pressure of 1.5MPa to investigate the influence of the nozzle...

Recent efforts to investigate car-park fires and understand the related mechanisms have fostered the need for analyses of suppression performance against this type of fire scenario. This work aims at providing an insight into the ability of sprinklers and water-mist systems to control and extinguish a fire within an enclosed car park through a series of real-scale experiments. Three cars were employed in each test: the central one was ignited by a heptane pool fire and the adjacent ones served as targets. Two configurations were explored: in the first one, a nozzle was placed directly at the vertical axis of the ignition source, whereas the ignition source was located between the area coverage of four nozzles in the second one. The sprinkler system mainly served as a reference; two values of discharge density were evaluated for water mist at high operative pressure and a biodegradable surfactant was also tested against the most challenging configuration. A quantitative analysis of free-burn and discharge phases by temperature measurements was coupled with radiant heat-flux measurements and an assessment of post-fire damage. Sprinkler and water-mist systems were capable of containing the fire spread and thermally controlling the fire, thus preventing structural damage. The water mist’s ability to overpower the plume and reach the burning surfaces proved more effective than that of sprinklers, especially as no nozzles were located right above the ignition surface. The higher discharge density showed better capability of preventing re-ignition phenomena and suppression was attained in both the investigated configurations, which suggests that a certain amount of flux is also needed to achieve flame cooling. The additive had promising impact on suppression performance; however, more tests are required to specifically explore its ability to enhance thermal control.

As a clean fire extinguishing agent, water mist has been considered to be an alternative to Halon 1301 on shipboard. Recently, a new water mist system was designed for large shipboard machinery spaces. In order to test the fire suppression performance of this system, a full-scale shipboard machinery compartment having a volume of 1200 m3 was built. In this compartment, five fire scenarios, including diesel spray fires, diesel tray fires, and wood crib fires, were designed, and fire suppression parameters, including extinguishment time, compartment temperature, and gas concentrations, were measured. For all the scenarios, extinguishment times were typically less than 1 min, except for small fires. Average compartment air temperatures dropped to 70 °C within seconds after mist was activated. The CO concentrations of all the scenarios were below 4000 ppm, which was not life-threatening for short-term exposures. The test results indicated that this water mist system had an excellent ability to extinguish both obstructed and unobstructed Class B tray fires, Class B spray fires, and Class A fires in large machinery spaces. Meanwhile, the system could minimize the thermal damage to the compartment and its infrastructure and provide favorable conditions for personnel evacuation and firefighting. In conclusion, this newly designed water mist system was a viable alternative to Halon 1301 system for protecting large machinery spaces.

A new tunnel fire detection and suppression system based on camera image processing and water mist jet fans

This study aims to experimentally investigate the combustion products of fires suppressed/extinguished by two water-based fire suppression systems, namely, sprinklers and water mist systems. A total of thirteen experiments were conducted with various suppression system configurations, i.e., with a sprinkler, a low-pressure (LP) water mist, and a high-pressure (HP) water mist, at operating pressures ranging from 2 to 60 bar and water flow rate ranging from 10 to 206 L/min. Each experiment was conducted twice, except for the baseline experiment with no suppression. The fuel was a high-density polyethylene (HDPE) pallet placed on two wood pallets. During all the stages of fire development, suppression with water, and post-suppression, the combustion products were sampled through Fourier-Transform Infrared Spectroscopy (FTIR) using a gas analyzer capable of operating in high humidity. The main combustion products identified were CO2, CO, and H2O. In addition, NOx (nitrogen oxides), CxHy (light-weight hydrocarbons), and HCN were present in relatively high concentrations. All the tested fire suppression systems were effective in reducing the fire size and cooling down the gases. However, when the fire could not be immediately extinguished, the NOx, CxHy, and HCN concentrations were higher than those in the baseline experiment. Moreover, it is observed that the HP water mist system was more effective than the sprinkler and low-pressure water mist systems in reducing the amount of combustion gases during suppression, resulting in lower Fractional Effective Doses (FED). It was observed that the combustion products returned to ambient conditions after five minutes of deactivation. The results from this study provide much-needed validation data for the effectiveness of water-based suppression systems, not only in reducing the fire size but also in reducing the production of acute toxic gases, which is important for considerations regarding evacuation, firefighting, and post-extinguishment conditions.

Due to the advantages of no pollution, rapid fire suppression, less water consumption, lower cost, and little damage to the object, water mist fire extinguishing system has been widely used in road tunnels. In order to improve the fire extinguishing performance of water mist fire extinguishing system, a water based extinguishing agent was used as additive and injected into the water mist fire extinguishing system at the proportion of 3%. The tunnel fire suppression tests were carried out, and the fire extinguishing performance of water mist fire extinguishing system under different longitudinal ventilation velocity and with and without additive were compared and analyzed. The results show that high pressure water mist system has good cooling and heat radiation blocking effect, and has good fire control and extinguishing effect for tunnel oil fire;the suitable additive can effectively improve the fire control and extinguishing effect of water mist extinguishing system used in road tunnel.

The objective of the project is to develop water mist extinguishments design by scaling. The report describes the requirement and criteria of scaling fire, scale model, and the results of suppression for a developing water mist system design. The Maritime Safety Committee Draft Circular, MSC 914 is used as a basis test to evaluate a water mist design. A series of three full-scale tests related to MSC 914 were performed: fire only, fire with steel trailers, and fire with steel trailers and combustible commodities. A simulation was accordingly studied. Then, a scaled water mist design was tested in the scale model to find the characteristics needed for suppression in terms of pressure, water flow rate, droplet size, and the spray momentum. Based on these characteristics, a candidate nozzle will be selected for the full-scale MSC 914 test. The results so far show that the water mist system can effectively suppress the fire in scaled MSC 914 model. The full-scale MSC 914 is scheduled for September 2001. Therefore, the final answer is still pending until then. Scaling results are confirmed for temperatures, heat flux and flow for the MSC 914 fire without water add in.

Numerical Study on the Effects of Ambient Air Pressure on Water Mist Characteristics

This study investigates how high‐pressure water–mist system discharge methodologies influence the fire extinction performance for pan pool fires and the corresponding mechanisms of restraining fire. The fire source is a pool‐fire burner. Fine water spray is injected using a portable device. The additive in the water–mist is neither toxic nor corrosive. All the tests are regarded as fuel controlled. The fire test parameters are fuel type, nozzle discharge angle, and additive solution volume. The fuels used are heptane, gasoline, and diesel. Nozzle discharge angles are 30, 45, and 60° with respect to the ground. Additive solution volumes are 0% (pure water), 3, 6, and 10%. Test results indicate that the nozzle discharge angle and additive solution volume in a water–mist fire extinction system play a significant role. Fire extinguishing efficiency is influenced by mist effects and the additive. Furthermore, the water–mist system can reduce radiation and can provide good protection for operators using portable fire extinguishing equipment. Copyright © 2008 John Wiley & Sons, Ltd.

Interaction of fires with water have been a focus of study for human kind from the times immemorial. With the recent advances in water-based suppression, and restrictions put on halon usage, sprinklers and water-mist based fire suppression systems have become popular for industrial usage. Of this water mist is an interesting candidate, for it has advantages and to name a few would be less water requirement, non-wetting nature, gas phase action on fire. Water mist, as an effective fire suppressant, works on the principle of oxygen dilution and flame cooling.In this work, we are studying the action of water mist on a diffusion flame. The water mist was generated from a Delavan nozzle, fed with high pressure water, which is then directed downward into the raising flame. A circular burner fed with Methane in a controlled manner generated the diffusion flame. The reason to prefer a gas burner is to have a control over heat release rate which will help in simulating various fuel sources of different burning rate. A glass cubicle was used to isolate the experiments from ambient disturbances. A Digital SLR camera was used to record the flame and subsequently the images were processed to obtain flame height. Particle Image Velocimetry was used to study the effect of the flame on the water mist., by imaging the Mie scattered laser light from the droplets. Parameters that were varied were the injection pressure and flow rate of the Methane into the burner.Visual imaging from the camera indicated that there were occasional flame tip flattening during the suppression mechanism. The flame luminosity is diminished and the diffusion flame height is reduced due to the action of the water mist. Moreover, this effect is more pronounced for smaller flame than larger flame, indicating the role of the buoyancy in fire suppression effectiveness. The PIV results show that the droplets are slowed down very close to the nozzle due to the flame. Also, a recirculation zone is observed at the periphery of the spray cone, very close to the nozzle. It is a toroidal vortex that is generated due to the interaction, and the droplets thrown away from the spray cone gets trapped into this flow. The flow structure is present in a highly turbulent region and is identified in the mean field. Another finding is that close to the burner, fine droplets that could make it to the base, gets entrained into the flame. It is expected that the droplets tend to be entrained into the larger flame, as the entrainment is stronger for large flame, compared to the smaller flame. But the PIV results indicate otherwise, which is attributed to the larger size of droplets making its way close to the burner.We believe that these results will enlarge our understanding of the suppression mechanism of water mist and could form a basis for validating various simulation models.

A twin-fluid water mist fire suppression atomizer is designed, developed, and analyzed. Of primary interest is the development of a twin-fluid atomizer that produces a large droplet diameter and velocity distribution and also produces a mist with sufficient cone angle to be effective in fire suppression applications. Spray characterization experiments are conducted utilizing Phase Doppler Particle Analysis (PDPA). The effect of atomizer nozzle geometry on internal two-phase flow and resulting spray pattern is investigated. National Fire Protection Association (NFPA) Standard 750 characterization experiments are conducted to verify that the sprays produced by the developed atomizer are classified as a water mist as defined by the Standard. Water mist sprays are produced using three different atomizing gases: Carbon Dioxide, Helium, and Nitrogen. PDPA measurements obtained utilizing all three gases are compared and analyzed. Full-scale fire suppression experiments are conducted using the developed twin-fluid atomizers. Identical experiments are conducted with a commercially available water mist atomizer to provide a basis for comparison. Fire tests are conducted on Class B fires consisting of pool, spray, jet, and simulated machinery space fires. The locations of the fires relative to the atomizer are varied to study the effects of atomizer position on fire suppression performance. The results reported herein indicate the atomizer’s ability to rapidly extinguish Class B fires. Also, the mechanisms of extinguishment for each fire scenario are described. Particle Image Velocimetry (PIV) measurements are conducted on charged droplet sprays. A Spray Triodeâ electrostatic atomizer is utilized to study the effects of charged droplet sprays with varying electrical boundary conditions near the exit of the atomizer. The boundary conditions near the atomizer are varied by placing grounded and ungrounded obstructions in the spray flow field. The experimental results indicate .the charged droplet’s ability to wrap around objects and sustain counter gravity flow.