Physical Scaling for Performance Evaluation of Water Mist Systems in Enclosures

1. Physical Scaling for Performance Evaluation of Water Mist Systems in Enclosures Hong-Zeng (Bert) Yu, FM Global Research Jonathan Carpenter, FM Approvals Fire Sprinkler International May 20-21, 2014 London, United Kingdom

2. Outline • Motivation • Review of the scaling laws • Scaling law validations • A test case for scaling up water mist protection • Approval process of FM Approval Standard 5560 using scaling approach • Summary

3. Why scale water mist fire suppression? • To reduce the development cost of water mist fire protection systems in enclosures. • Currently, full-scale testing is required for system development and listing. • Often times it is a trial-and-error process • Full-scale fire testing costs are often prohibitive for niche applications. • Goal: To replicate water mist fire protection with scaled-down facilities.

4. In geometrically similar control volumes, • Conserve: • Froude number of gas flow Froude-Based Physical Scaling Principles • Momentum transfer characteristics between water droplets and gas flow. • Droplet vaporization characteristics. • Scalar quantities in the control volumes.

5. Froude-Based Scaling Relationships * Fire Safety Journal, 2012.

6. A Scaling Illustration for Red <1 Full Scale 20 x 20 x 10 m high Enclosure 4 x 4 m Door Opening 1/4 Scale 5 x 5 x 2.5 m high Enclosure 1 x 1 m Door Opening Fire size 6000 kW 188 kW (S2.5) Water mist discharge rate 100 liters/min 3.1 liters/min (S2.5) Droplet size 90 microns 64 microns (S0.25) Water mist discharge time 30 s 15 s (S0.5)

7. Validations of Scaling Relationships • Droplet size dependence on Red (Scale ratio = 9 :1) (Fire Safety Journal, 2008) • Spray cooling in open space (Scale ratio = 9:1) (Fire Safety Journal, 2008) • Fire radiation effect (Scale ratio = 9:1) (Fire Safety Journal, 2012) • Fire suppression and extinguishment for different fuel types in enclosures (Scale ratio = 3:1) • Gas fires (propane) (9th IAFSS Symposium, 2008) • Pool fires (heptane) (10th IAFSS Symposium, 2011) • Solid combustible fires (wood cribs) (11th IAFSS Symposium, 2014)

8. Pool Fire Suppression in Enclosures Scale-3 Enclosure: 3.66x3.66x3.66 m Door Opening: 0.91x1.83 m high 1.83x1.83 m high Scale-1 Enclosure: 1.22x1.22x1.22 m Door Opening: 0.30x0.61 m high 0.61x0.61 m high

9. Scaling Pool Fires in Open Space -1 Scale-3 Heptane Pool Fires ( Scale-1 Rate x 32.5):0.55-m pool  390 kW 0.74-m pool  900 kW Scale-1 Heptane Pool Fires:Smaller fire: 0.23-m diameter pool  25 kW Larger fire: 0.32-m diameter pool  58 kW

10. Test Conditions

11. Fire Locations and Measurements • Fire heat release rate • Floor-level oxygen concentrations

12. Scalability Evaluation for Pool Fire Suppression Replicate • Fire extinguishability. • Fire heat release rate with time. • Oxygen concentrations.

13. Ignitable Liquid Cut-Off Room Challenges: 1) low flash point liquids. 2) large door openings. 3) high ceilings. 4) ceiling nozzles only. 5) obstructed fires.

14. Ignitable Liquid Cut-Off Room Protection* Targeted cut-off room and fire hazard: 1) Cut-off room size: 7.47x7.47x7.47 m high (6 times the Scale-1 enclosure) 2) Door opening: 3.66x3.66 m high (6 times the Scale-1 enclosure’s larger opening) 3) Heptane storage tank: 1.83 m diameter x 2.74 m high, 0.91 m above floor. 4) Fire scenario: Cascading heptanespill from the top of tank at 38 liters/min . (~ 8 MW > 5.1 MW = 58 kW of Scale-1 fire x 62.5) Based on the water mist protection for the Scale-1 enclosure,the water mist requirement for the cut-off room is: *Journal of Fire Protection Engineering, 2013.

15. Key Components for the Scaling Approach Three key components: • Nozzle spray characterization (droplet size and distribution, spray discharge rate and momentum, spray angle and flux distribution pattern, etc.) • Well mixed model – a predictive tool to assess the total water mist discharge rate and droplet size for full-scale protection, for screening purpose. • Scaling methodology to scale down the large-scale fire tests.

16. Approval Process for the Scaling Approach After implementing the scaling approach to FM Approval 5560 – Water Mist Systems: • Manufacturer applies for FM Approval with parameters for full-scale protection and supplies scaled-down nozzles to FM Approvals. • FM Approvals assesses the adequacy of the intended full-scale protection parameters with the well-mixed model using data from the scaled-down nozzle characterization activity. This is a screening approach to identify a potential solution that works. • Conduct testing in the scaled-down mockup with the scaled-down protection parameters and nozzles to ensure fire extinguishment results. • Manufacturer submits the full-scale nozzle for spray characterization to ensure meeting the scaled-up requirement. • Approval granted for full-scale protection by scaling up the scaled-down test results according to the scaling relationships.

17. Current Approach – Full Scale Testing

18. New Approach – Reduced Scale Testing

19. Benefits to Industry • Potential reduction in approval cost and time • Potential reduction in internal cost to the manufacturer could be significant due to the screening test availability. • Potential reduction in required number of reduced-scale tests in the future (after gaining some experience) • Ultimately increase the number of certified applications!

20. Summary • The Froude-based scaling laws have been validated with laboratory experiments for the effects of droplet size, fire radiation, enclosure and different types of combustibles. • The protection of an ignitable liquid cut-off room has been successfully developed by scaling up the known protection requirements for smaller enclosures. • The approval process based on the scaling approach is to be implemented in FM Approval Standard 5560 – Water Mist Systems, to help reduce the system development and approval cost and increase applications.

21. Questions ?