Inflatable Smoke Barriers To Enclose Stairs, Halls Devised By Tokyo F. D. Science Lab
Rapid smoke spread during a fire in a high-rise building or an underground arcade can be a terrifying threat to life that can be averted by the use of inflatable smoke barriers developed by the fire science laboratory of the Tokyo Fire Department.
The rolling steel shutters that are used in Japan to close off passageways are usually ineffective in preventing the movement of smoke past them and may even trap people when they close.
The inflatable smoke shutter developed by the fire science laboratory is one of the most convenient and effective ways of shutting off rapid smoke flow in horizontal spaces and vertical shafts. Air curtains used at department store entrances gave us the idea for our inflatable smoke shutters.
Like an air cushion
When inflated with inert compressed gas or air, the smoke shutter looks like an air cushion. It is designed so that all its edges touch the walls, ceiling and floor of a corridor to block off all air movement. Moreover, it enables persons to pass through the shutter by simply pushing its edge aside for immediate passage and it lets us easily and rapidly remove heavy smoke trapped behind the shutter by using air blowers and smoke ejectors.
There are two types of inflatable smoke shutters. One type is designd for permanent installations and the other is a portable model that fire fighters can carry into a building.
The use of permanent instead of portable shutters is advisable because the permanent shutter can be designed for an exact fit in a specific location. Permanent installations also can be made in any type of vertical shaft, including air-conditioning ducts. Portable shutters can be made to fit various structural measurements by incorporating multiple compartments in the shutter body.
How inflatable shutters are installed to enclose a stairway is shown in Figure 1. Usually the shutter body (1) is folded into a box (2) and held in place by a board (3) which is part of the ceiling. One side of the board is hinged and the other side is released by a trigger (4) that is activated when a smoke detector (5) operates, transmitting an electrical signal to the trigger.
The folded shutter falls free to curtain off the corridor. A simple transistorized circuit and a resistor provide a selected interval of delay, preferably 15 seconds, before a valve (6) releases compressed air or gas from a tank (7) to inflate the shutter. The delay interval, provided by the resistor, allows enough time for the shutter to unfold completely before inflation.
It is recommended that the shutter be inflated with carbon dioxide mixed with 10 to 15 percent nitrogen. The size of the shutter determines the capacity of the compressed gas storage tank. Instead of compressed gas, a shutter can be inflated by a fan set to run for a predetermined time.
There are emergency exits with short tubes in the lower part of the shutters so that building occupants and fire fighters can pass through these barriers.
In shafts or ducts, such as air-conditioning ducts, inflatable smoke shutters can be installed much the same as they are permanently installed in corridors. The shutters, placed at strategic points, are inflated through the activation of smoke detectors.
A number of inflatable smoke shutters can be installed in a building and connected serially so that they can be actuated manually or by smoke detectors. They can also be operated from an emergency control room in a building.
Shutters easily folded
Portable inflatable smoke shutters for use by fire companies are light in weight and are easily folded for storage on fire apparatus.
The portable shutters have a looped compartment surrounding the main body of the unit (Figure 2). To fit the shutter in a corridor or stairway area, the main body is first inflated and then the looped compartment is inflated until its edges touch all four adjacent surfaces. These shutters are inflated from tanks of compressed gas or air, or even by fans, at the place where they are to be set up. During our tests, we found that even a home vacuum cleaner was able to inflate the shutters.
An interesting feature of the inflatable smoke shutters is that a fan can be used to blow 17,500 to 35,000 cfm of air through the emergency exit into a stairwell to keep this evacuation route clear of smoke.
The material used in the shutters is» woven from 21-denier nylon yarn, providing a weight of 3.3 ounces per square yard. The cloth has a neoprene coating of 15 1/2 ounces per square yard.
The nylon cloth has a tensile strength of 220 pounds vertically and 198 pounds horizontally with a tear strength of 17.6 pounds vertically and 22 pounds horizontally. The elongation rates are 25 percent vertically and 30 percent horizontally.
When inflated, the permanent installation inflatable shutter is 5 ft, 11 in wide, 8 ft, 3 in high and 1 ft thick. The main body of the portable shutter, when inflated, is the same size. The outer, looped, compartment of the portable shutter when inflated provides a total width of 7 ft, 11 in; a height of 10 ft, 2 1/2 in; and a thickness of 1 ft.
The standard inflation pressure of the shutters is 0.288 to .434 psi, or 8 to 12 inches water column. The pressure range can be compared to the atmospheric pressure in a burning room, which is estimated at 0.00434 psi to 0.01 psi above normal, or 0.12 to 0.28 inches water column.