Fire Protection Research Foundation report: “Vapor Mitigation Testing Using Fixed Water Spray System"
Authors: Murtaza I. Gandhi, P.E., Alex Fergusson, Joseph Kao, Jin Zhao, Ph.D., P.E., Baker Engineering & Risk Consultants, Inc.
Date of issue: April 2019
Fixed water spray systems may be designed to mitigate flammable vapors and they work primarily by entraining air into the spray cone and mixing the air and water droplets with the flammable vapor, thereby diluting the vapor. It should be noted that this project is to determine the design criteria if fixed water spray should be activated upon confirmed gas detection, and not intended for explosion suppression. However, exercise care when selecting this approach because some research have shown that congested areas (example offshore platforms) may cause increase of explosion because of the turbulence generated by water spray.
The current industry standards including API RP 2030: Application of fixed water spray systems for fire protection in the petroleum and petrochemical industries and NFPA 15: Standard for water spray fixed systems for fire protection, while providing information on vapor mitigation using fixed water spray (section 7.5), do not provide the design criteria on how much water and pressure is required to effectively mitigate a specified minor vapor leak, but does specify that the minimum rate of water application shall be based on field experience or actual test data.
The goal of this research project is to evaluate the effectiveness of fixed water sprays to prevent the development of flammable vapor clouds and control the fire in case of ignition. The specific objectives are to provide test data to develop a design criteria on how much water and pressure is required to effectively mitigate:
- Specific leaks of saturated propane, propane vapor and methane vapor.
- At specific vapor leak rates of 0.1 kg/s and 0.3 kg/s.