«ENGINEERING PERFORMANCE OF WATER MIST FIRE PROTECTION SYSTEMS WITH ANTIFREEZE A Major Qualifying Project Report Submitted to the Faculty of WORCESTER ...»
Project Number: MQP KZN 990
ENGINEERING PERFORMANCE OF WATER MIST
FIRE PROTECTION SYSTEMS WITH ANTIFREEZE
A Major Qualifying Project Report
Submitted to the Faculty of
WORCESTER POLYTECHNIC INSTITUTE
in partial fulfillment of the requirements for the
Degree of Bachelor of Science
Matthew S. Connolly _________________________________
Stephen M. Jaskolka _________________________________
Jeffrey S. Rosen _________________________________
Michael D. Szkutak Date: 26 April 2012
Professor Kathy Notarianni, Primary Advisor Keywords
2. Water Mist
3. Heat Release Rate Professor David DiBiasio, Co-Advisor 1 Table of Contents
Water mist and traditional sprinklers
Fire suppression systems in subfreezing environments
Challenges of antifreeze in fire suppression
Selection of antifreeze agents and concentration
Selection of antifreeze agents for study
Selection and verification of antifreeze solution concentrations
Measurement and evaluation of agent properties
Fire scenario interactions
Spray performance variables
Potential risk of system failure
Summary of variable categories
Results and discussion
Fire scenario interactions
Spray performance variables
Potential risk of system failure
Summary of key study variables
Figure 1. System testing set up
Figure 2. Example test data: heat release rate (HRR) vs.
time and normalized HRR vs.
Figure 3. Normalized heat release rate (HRR) with pure water discharge vs.
Figure 4. Low pressure normalized heat release rates (HRR) with propylene glycol (PG) discharge vs.
Figure 5. High pressure normalized heat release rate (HRR) with propylene glycol (PG) discharge vs.
Figure 6. Low pressure normalized heat release rate (HRR) with glycerine (GLY) discharge vs.
Figure 7. High pressure normalized heat release rate (HRR) with glycerine (GLY) discharge vs.
Figure 8. Normalized heat release rate (HRR) with betaine discharge vs.
Figure 9. Low pressure normalized heat release rate (HRR) with potassium acetate (KA) discharge vs.
Figure 10. High pressure normalized heat release rate (HRR) with potassium acetate (KA) discharge vs.
Figure 11. Summary of the normalized heat release rate (HRR) contribution to the fire for all tested antifreezes
Figure 12. Kinematic viscosity relative to pure water at 4°C for antifreeze solutions freezing at -20°C
Figure 13. Kinematic viscosity relative to pure water at 4°C for antifreeze solutions freezing at -40°C
Figure 14. Density of each test solution and pure water at 25°C.
Figure 15. Relative surface tension of each tested solution as compared to pure water.
Figure 16. Summary of the volumetric expansion coefficients of antifreeze solutions compared to water
Table of Figures
Table 1. Comparisons of Traditional Sprinklers and Water Mist Sprinklers [4,5]
Table 2. Solution Concentrations to Benchmark Freezing Points (wt.
Table 3. Corrosion rates (μm/yr) of copper and stainless steel samples
Table 4. Summary of the study variables ranked from highest to lowest property value.
Table 5. Suitability of tested antifreeze solutions for use in water mist systems
3 Abstract The use of antifreeze in a water mist fire suppression system offers a potential alternative to the current applications of these systems in subfreezing environments. Design and development of these systems however, would require quantitative data on the effect of factors such as small droplet sizes and/or higher system pressures which is currently unknown. This study investigates the use of antifreeze of various chemical compositions and concentrations in water mist systems by measuring and quantifying variables that affect spray characteristics, indicate the potential risk of system failure, and evaluate the interactions of the discharged agent with the fire. Extensive testing and analysis demonstrated that no antifreeze solution behaves ideally with respect to all three categories of variables; however some antifreeze solutions are potentially suitable in certain applications. Some of the antifreezes tested should not be used above a certain concentration in high pressure systems due the solution flammability and the resulting contribution to the heat release rate of the fire. The impact of all other tested pressures and concentrations on the heat release rate of the fire was less significant, and these solutions are potentially suitable for use in water mist systems once spray performance and potential risk of system failure are considered.
Ignitibility of the antifreeze discharge was proven to be a function of antifreeze solution concentration and droplet size. Future testing should determine the threshold droplet size for ignition of antifreeze discharge and at what point changes in antifreeze solution properties begin to significantly impact droplet size in subfreezing environments.
4 Introduction The use of antifreeze in a water mist fire suppression system offers a potential alternative to the current applications of these systems in subfreezing environments. Water mist systems are currently used to provide fire suppression in many types of commercial and industrial hazards, including marine applications, historic buildings, and electronic equipment rooms . Where portions of the system are exposed to subfreezing temperatures in these applications, alternatives to the conventional wet-pipe system are required to ensure proper operation. Traditional sprinkler systems have solved this issue by removing the water from the pipes using dry-pipe systems, or through the addition of antifreeze agents in portions of the system piping. This provides two unique solutions which allow for fire suppression in subfreezing environments and the application will dictate which solution is most appropriate.
In water mist systems however, dry-pipe systems have been accepted, yet antifreeze-protected systems have yet to be widely used. An antifreeze-protected water mist system may be advantageous over dry-pipe systems when water delivery time is important, the entire system is not subject to freezing, or when adequate compressed gas cannot be delivered to pressurize the system during non-activation periods. However, it is unknown how a water mist system utilizing an antifreeze solution would perform with respect to spray performance, potential risk of system failure, and interactions of the discharged agent with the fire. This lack of technical knowledge regarding the incorporation of antifreeze into water mist systems has prevented the widespread development and acceptance of such systems thus far.
Water mist and traditional sprinklers Two forms of fire suppression commonly utilized in subfreezing environments are traditional sprinkler systems and water mist systems. Although fine sprays were known to be effective, the first significant work involving water mist systems was conducted by UL in . Water mist systems garnished more interest in the early 1990’s, following the international adoption of the Montreal Protocol. This restricted the production of ozone-depleting chemicals and resulted in the phasing out of Halon in favor of more environmentally friendly fire suppression technologies . In 1996, the National Fire Protection Agency (NFPA) published NFPA 750: Standard on Water Mist Fire Protection Systems, the first fire protection standard on water mist. This standard defines water mist as a spray for which 99% of the mass of a representative sample of the spray is contained in droplets with diameter less than 1000 microns .
The components and operating conditions of a water mist system differ significantly from those of a fire sprinkler system. Table 1 highlights these differences with respect to droplet size, operating pressure, volumetric flow rate, nominal system pipe diameter, and pipe material. The primary advantage of water mist over traditional sprinkler systems is the reduced water demand resulting from the higher operating pressures and lower volumetric flow rate . Lower water flow rates allow for reduced pipe size, which decreases the overall system weight, simplifying installation. These benefits make water mist systems an advantageous alternative to traditional sprinkler systems in specific applications where low water discharge is crucial, such as museums, and where lower system weight is crucial, such as on ships.
The spray density and droplet size distribution produced by a water mist system result in additional extinguishing mechanisms as compared to a traditional sprinkler system. In a traditional sprinkler system, the primary extinguishing mechanisms are absorption of heat and wetting of the fuel source. Heat is absorbed by the spray itself as it penetrates the fire plume and reaches the fuel surface or when the drops vaporize upon contact with the superheated air surrounding the fire. This is aided by the wetting of the fuel source since the water must be driven off the fuel before it can continue to vaporize and ignite. In addition to these mechanisms, in water mist systems, the small water mist droplets also displace oxygen and dilute fuel vapor . As the droplets absorb heat and evaporate into steam, they expand up to 1700 times in volume and push away the surrounding gases. The addition of water vapor to the gas mixture also dilutes the fuel vapor reducing the flammability of the mixture.
Fire suppression systems in subfreezing environments Traditional sprinkler systems utilize two different system arrangements to protect against fire in subfreezing environments: dry pipe systems and wet-pipe systems where piping exposed to subfreezing temperatures is filled with antifreeze solution. A dry-pipe system utilizes pressurized air, nitrogen, or inert gas to keep a valve shut, preventing water from entering the system piping until the system is activated . The purpose of this design approach is to allow for effective fire suppression in subfreezing environments without concerns of water freezing in the pipes. A wet-pipe antifreeze system, on the other hand, relies on antifreeze to protect exposed portions of the system piping from freezing, and upon activation, discharges the antifreeze solution on the fire, followed by water.
A wet-pipe antifreeze system may be advantageous over dry pipe systems when water delivery time is important, the entire system is not subject to freezing, or when adequate compressed gas cannot be delivered to pressurize the standby dry system . This holds true for both traditional sprinklers and water mist systems, and indicates that a wet-pipe water mist system protected with antifreeze merits consideration. However, the use of antifreeze in water mist systems to support various applications in subfreezing environments has not been considered; unlike traditional sprinkler systems, the only current application of water mist systems in subfreezing environments has been with a dry pipe system. Concerns in industry regarding the integration of antifreeze into water mist systems have prevented the widespread development of such systems. These concerns, including changes in spray performance, potential risk of system failure, and interactions of the discharged agent with the fire, have resulted from incidents involving the integration of antifreeze in traditional sprinkler systems.
6 Challenges of antifreeze in fire suppression The use of antifreeze in traditional sprinkler systems has been regulated in National Fire Protection Association (NFPA) codes since 1940 . However, despite decades of safe and effective use, there have been a few recent accidents which have caused doubts about the safety of antifreeze in these systems. In 2001, an overhead heater at a restaurant caused a traditional sprinkler system, protected with an unknown concentration of propylene glycol solution, to activate. Propylene glycol vapors from the discharged solution caused a flash fire when they interacted with the heaters. The resulting flames traveled across the ceiling towards surrounding occupants, injuring 19 people . The fire was extinguished by the pure water discharge from the sprinklers once all of the antifreeze solution was discharged. In 2009, a traditional sprinkler system protected with a 50% glycerine solution may have contributed to a fatal explosion in a kitchen fire . As a tenant was placing a frying pan with flaming contents under his kitchen sink faucet to extinguish the fire, the sprinkler overhead activated and the principle investigator reported that upon the interaction of glycerine with the flames from the frying pan, an explosion occurred .