Automatic Smoke & Fire Curtains.

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Shevs.

Smoke Control using the " Cabin Principle ": Pros and Cons of SHEVS and of Depressurisation.

Abstract.

Many large modern buildings, most typically airport terminals, have many well-separated retail units within a much larger space. The Cabin Principle has been used in several airport terminals and elsewhere, to contain any fire smoke in the unit on fire, thus removing the need for major fire precautions in the main space where that space has little potential fuel.

The usual application of this principle is similar to the long-established technique of the large-scale experimental calorimeter. This application has the retail unit forming an open-fronted, and/or open-sided box, and uses the methods of smoke and heat exhaust ventilation ( SHEVS ) to contain smoky gases within a smoke reservoir formed in that box. This approach is described in this paper as the " SHEVS " Cabin" principle. Calculation procedures are described, based on existing practice for SHEVS, and an example is presented. Advantages and disadvantages of the technique are discussed. The following conclusions are reached:

x    For the example cited, the optimum fan capacity is about 11.3 m³s^-1.

x    The successful operation of sprinklers in the cabin is essential.

x    The design is not tolerant of failure in any of the equipment.

x    Even in a successful design some smoke will leak past the edges of  Automatic Drop Curtains into the space outside the cabin. Whether this creates a hazardous condition or not depends on the volume of that space and the role and performance in emergency of any HVAC system in that space.

x    Curtain deflection is trivial and can be ignored for the case of the cabin dimensions used in the example. Note that this conclusion cannot automatically be generalised to apply to other examples.

x    The operation of sprinklers may cause some smoke to spill beneath the curtains unless the curtains can be made deeper - although this cannot be calculated. This could in some circumstances make the curtains close to or below head height for some people who might have to escape below it.

x    The curtain material should be able to withstand flame temperatures. This is a more rigorous specification than is usual for most applications of  smoke curtains.

x    Fire safety management provisions to ensure continuing function of all equipment is essential.

x    Fire safety management must include a "policing" role to prevent potential fuels being placed outside the cabin.

A novel alternative principle is developed based on closure of the front of the retail unit's "box" using an automatic drop curtain, combined with a controlled reduction of pressure within that box to prevent any leakage of smoke from the unit into the large space outside. Calculation methods for this "Depressurised Cabin" principle are presented, and a worked example is used to allow direct comparison with the SHEVS approach. The conclusions reached are:

x    The cabin should have fire-resisting walls and ceiling.

x    The Automatic smoke curtain at the front opening should have a bottom bar which moves freely in vertical tracks fastened to the side walls of the cabin.

x    This curtain should be able to withstand flame temperature gases of at least 1000 ^oC.

x    The curtain must be full height, with its bottom bar resting on the floor.

x    The curtain should be longer than the vertical height to the floor, with a fabric length calculated to be sufficient to prevent the bottom bar lifting.

x    The weight of the bottom bar should be specified as part of a design trade-off with the overall fabric length, in order to optimise intrusion of the curtain into the retail space. For the example cited a bottom-bar weight of 10 kgm^-1 appears suitable.

x    A relatively small exhaust fan, of 1.75 m³s^-1 for the example's dimensions of cabin, should be used to achieve the reduction of pressure in the cabin.

x    The cabin should have a barometric damper set to open at 60 Pa. For the example cited the damper should have a minimum aerodynamic free area of 0.18 m².

x    There must be an escape door (or more than one if required by local Means of Escape rules) from the cabin for people to escape after the curtain has operated. This door should be identified by appropriate signage.

x    The system is tolerant of failure of all components except the smoke curtain, which must work properly. This implies that the management of the Terminal Building must include regular, frequent, functional tests of the curtain during normal use.

x    As in the case of the SHEVS cabin, the fire safety management should include a "policing" role to prevent potential fuels being placed outside the line of the smoke curtain, and also to ensure that the fall of the curtain is not blocked.

It is noted from the example calculated that the exhaust fan capacity required for depressurising can be an order of magnitude smaller than for the SHEVS Cabin approach.

A Fire curtain in a factory in Gateshead

Our Fire curtain  Ltd products can provide the benefits of an off the shelf lightweight design which eliminates the problems of steel shutters. The Fire curtain requires less preparation time and may not need any special steelwork structure for the installation.

Designed for openings of up to 30m wide by 8m high in the fire compartment wall. It eliminates the dangers posed by heavy steel shutters which could drop, causing casualties or breakages. It is especially suited to clean hygienic environments such as kitchens and hospitals, or is equally at home over windows and reception areas

Slim, lightweight, easy to install and standard sizes for supply only but we can still make to order.

2hour fire resistance to BS476 Part 22 and Smoke control to BS7346 Part 3

Sealed to prevent the passage of fire or smoke

Total power failure if the gravity fail safe system is requested and with a safe controlled descent on all models.

Choice of alarm actuations such as fire or smoke sensors or directly from a fire alarm panel.

24V operation with battery back-up

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