New venting unit provides automatic pressure relief for use with fixed gas extinguishing systems.

October 99 Fire & Safety

A new pressure relief unit specially designed for use with fixed gas extinguishing systems was recently launched by SPI (Fire Engineering) at Fire Expo 99.

The wall-mounted unit, called Prespac, alleviates the risk of structural damage caused by over-pressurisation following the release of inert gas in a protected space. Prespac opens automatically when the positive pressure reaches 1,5 mb (150 Pascals). Unique weighted relief blades close to seal the enclosure as pressure equalises, maintaining the concentration of extinguishing gas at an effective level.

"Inert gas concentrations of 35% or more are normally required to extinguish fire in an enclosed space," explains David Adkins, SPI's Commercial Director. "Release of gas at such concentrations results in positive pressure which can lead to structural damage unless venting is provided. Normal build rooms will withstand an increased pressure of 5 mb (500 Pascals). Prespac comes into operation well before this level is reached."

The BFPSA Code of Practice stipulates that rigid elements of a protected enclosure must have a fire resistance of not less than 30 min. Compliance with this often necessitates the installation of a separate fire damper which would normally defeat the object of fitting an overpressure device. Prespac eliminates this problem, however, since it will maintain firewall integrity without the need to fit a separate damper.

Prespac has been independently tested by Chiltern Fire to the general requirements of BS478: Part 20: 1987, where it achieved over two hours' integrity.

Prespac is a compact unit, 350 mm2 which fits flush to the wall of a gas-protected area. Supplied with a grid cover, it resembles a wall-mounted fan or vent, providing a convenient and unobtrusive means of pressure relief.

For details contact Tony Bedlow of SPI (Fire Engineering) on tel: (0944) 1252 373 331 or fax (0944) 1252 373 332.

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