The LWF Blog
Fire Engineering Design and Risk Assessment – Foam System Discharge Devices – Part 6
June 6, 2018 11:43 amIn LWF’s fire engineering blog series for Architects and others in the building design business, we have been looking at methods of fire suppression. In part 5, the different types of foam system were outlined and in part 6, we take a look at what is available in terms of foam system discharge devices.
Foam Chambers
Used as a part of cone roof storage tanks, a foam chamber contains a vapour seal, the role of which is to prevent vapours escaping. The foam chamber itself comprises a foam maker or solution aspirator in addition to a chamber so that the foam can expand. Once expanded, it is expelled via a deflector plate down the inside wall of the tank.
Rimseal Foam Pourers
Floating roof tanks utilise rimseal foam pourers when they are fitted on top of the tanks to provide protection to the flexible seal area. The rimseal foam pourer comprises a foam aspirator or foam maker, along with a foam chute which directs the foam down the inside wall of the tank.
Subsurface Foam Units
Subsurface foam units aspirate the foam solution under the high back-pressure from the head of fuel in the tank and then the foam is discharged into the fuel where it rises to the surface. Semi-subsurface units can also be used, the main difference being that the semi-subsurface unit has a tube deployed within the tank to deliver the foam to the fuel surface.
Foam Water Sprinklers
Foam water sprinklers are positioned above process or fuel handling areas. The sprinklers comprise an air induction body into which the foam solution discharges. Once in place, the foam is aspirated by air drawn in through the body and the aspirated foam is then discharged evenly over a circular area with the use of a deflector plate.
Water Sprinklers and Sprayers
While conventional sprinkler systems usually deliver water into the area of fire origin, they can be used to distribute fluorosurfactant-based foams which require little or no aspiration. The foams available for use in this manner include AFFF, AR-AFFF and even FFFP in some cases.
Foam Branch Pipes and Monitors
Although foam branch pipes and monitors work in largely the same way as foam water sprinklers, they do not require the use of a deflector plate. They are capable of delivering foam over both horizontal and vertical distances to great effect, however, the plunging of the foam into the fuel can reduce effectiveness. It is possible to have a hand-held unit or a large capacity unit can be mounted on turrets or monitors which rotate and elevate. Foam branch pipes are most commonly found in areas such as bunds, process and handling, aircraft hangars etc.
Part 7 of this series will continue looking at foam system discharge devices from this point. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients for over 25 years to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact Peter Gyere on 020 8668 8663.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.