| [Home] | |
| |
|
By Anil Maheshwari, Managing Director
Caryaire Equipments India Pvt. Ltd., NOIDA
Anil Maheshwari is a mechanical engineer with 33 years experience in HVAC. He has worked 17 years for industry, 3 years as a consultant and founded Caryaire 13 years ago. He is a member of ISHRAE and ASHRAE.
Ducted air distribution systems in a centrally air conditioned building act as an easy passage for spread of fire and smoke when a fire occurs due to any reason. Fire dampers, smoke dampers or combination fire smoke dampers play a vital role in the management of fire and smoke in these cases.
Twenty years ago, the importance of these dampers, their construction, their testing, proper placement and installation in an air distribution system was not well appreciated or understood by many system designers, contractors and even the fire departments of large cities. Several disastrous fires that occurred during this 20 year span in New Delhi (Vigyan Bhavan, Hotel Vasant Continental, Gopala Towers, Ansal Bhavan, Uphaar Cinema) and Mumbai (State Bank of India, Express Towers) made the fire departments sit up and study the reasons for the fast spread of such fires and the loss of life.
At the State Bank of India building, Mumbai the firemen would finish putting off a fire, say on the 8th floor, and notice another fire starting on the 10th floor. Much later it was realized that a common shaft fed conditioned air to several floors from a common air handling unit and fire would spread from one floor to another via this common shaft. The most common insulation material used on ducts, in those early days, was Thermocole (a trade name for Styrofoam) wrapped with jute fabric, which could catch fire very fast and spread even faster. Smoke filled the staircase making entry and exit from the fire-affected building most difficult.
[top]
The National Building Code (NBC), which has a section devoted to air conditioning systems under “Building Services” was last published in 1983 and had very few recommendations on fire dampers and smoke management. Work started a year ago on the latest revision of this code and a group of experts from ISHRAE was formed for this task, which has been completed, and the draft revision is presently getting ready for printing. The relevant section is reproduced below:
•Air conditioning and ventilating systems shall be so installed and maintained as to minimize the danger of spread of fire, smoke or fumes from one floor to the other or from outside to any occupied building or structure
•Air conditioning and ventilating systems circulating air to more than one floor or fire area shall be provided with dampers designed to close automatically in case of fire and thereby preventing spread of fire or smoke and shall be in accordance with the accepted standard. Such a system shall also be provided with automatic controls to stop fans in case of fire, unless arranged to remove smoke from a fire, in which case these shall be designed to remain in operation.
• Air conditioning system serving large places of assembly (over 1,000 persons), large departmental stores or hotels with over 100 rooms in a single block shall be provided with effective means for preventing circulation of smoke through the system in the case of a fire in air filters or from other sources drawn into the system, and shall have smoke sensitive devices for actuation in accordance with the accepted standards.
• From fire safety point of view, it shall be preferable to provide separate air handling units for the various floors so as to avoid the hazards arising from spread of fire and smoke through the air conditioning ducts. The requirements of air conditioning ducts shall be in accordance with good practice.
• Though in normal building design, compartmentation plays a vital part in limiting the spread of fire, smoke will readily spread to adjacent spaces through the various leakage openings in the compartment enclosure, such as cracks, openings around pipes ducts, airflow grills and doors, as perfect sealing of all these openings is not possible. It is smoke and toxic gases, rather than flame, that will initially obstruct the free movement of occupants of the building through the means of escape (escape routes). Hence, the exclusion of smoke and toxic gases from the protected routes is of great importance.
• Pressurization is a method adopted for protected escape routes against ingress of smoke, especially in high-rise buildings. In pressurization, air is injected into the staircases, lobbies or corridors, to raise their pressure slightly above the pressure in adjacent parts of the building. As a result, ingress of smoke or toxic gases into the escape routes will be prevented.
• The pressurization levels for staircases should be as under :
| Building Height | Pressurization Level | |
|---|---|---|
| Reduced operation (Stage 1 of a 2-stage system) (Pa) |
Emergency Operation (Stage system or Single stage system) (Pa) |
|
| Less than 15 m |
8 |
50 |
| 15 m or above |
15 | 50 |
If possible, the same levels shall be used for lobbies and corridors, but levels slightly lower may be used for these spaces if desired. The difference in pressurization levels between staircase and lobbies (or corridors) shall not be greater than 5 Pa.
• Each basement shall be separately ventilated. Vents with cross-sectional area (aggregate) not less than 2.5 percent of the floor area spread evenly around the perimeter of the basement shall be provided in the form of grills, or breakable stallboard lights or pavement lights or by way of shafts. Alternatively, a system of air inlets shall be provided at basement floor level and smoke outlets at basement ceiling level. Inlets and extracts may be terminated at ground level with stallboard or pavement lights as before, but ducts to convey fresh air to the basement floor level have to be laid. Stallboard and pavement lights should be in positions easily accessible to the fire brigade and clearly marked ‘SMOKE OUTLET’ or ‘AIR INLET’ with an indication of area served at or near the opening.
• In multi-storey basements, intake ducts may serve all basement levels, but each basement level, and basement compartment shall have separate smoke outlet duct or ducts.
[top]
• Mechanical extractors for smoke venting system from lower basement levels
shall also be provided. The system shall be of such design as to operate on
actuation of heat/smoke sensitive detectors or
sprinklers, if installed, and shall have a considerably superior performance
compared to the standard units. It shall also have an arrangement to start it
manually.
• Mechanical extractors shall have an internal locking arrangement, so
that extractors shall continue to
operate and supply fans shall stop automatically with the actuation of fire
detectors.
• Mechanical extractors shall be designed to permit 30 air changes per hour in case of fire or distress call. However, for normal operation, air changes should be as per schedule given elsewhere in this code.
• Mechanical extractors shall have an alternative source of supply.
•Ventilating ducts shall be integrated with the structure and made out
of brick masonry or reinforced
cement concrete as far as possible and when this duct crosses the transformer
area or electrical switchboard, fire dampers shall be provided.
• All floors shall be compartmented with area not exceeding 750 m2
by a separation wall with 2 h fire
rating, for floors with sprinklers the area may be increased by 50 percent.
In a long building, the fire
separation walls shall be at distances not exceeding 40 m. For departmental
stores, shopping centers and basements, the area may be reduced to 500 m2
for compartmentation. Where this is not possible, the spacings of the sprinklers
shall be suitably reduced. When reducing the spacing of sprinklers, care should
be taken to prevent spray from one sprinkler impeding the performance of adjacent
sprinkler head.
[top]
The fire departments of all major cities have also framed standards of compliance that must be followed before a new building can be declared suitable for occupancy. Relevant extracts from such standards given by the Delhi Fire Service and the Mumbai Fire Department for a hotel building in each city are mentioned below.
While the general level of awareness of fire and smoke dampers among HVAC system designers has certainly improved, a lot more needs to be done at the level of contractors who, generally, prefer to buy the lowest price damper and install it with a minimum concern for the safety of people and property during a fire. What makes the problem of safety even worse is that all manufacturers of fire and smoke dampers do not necessarily have their dampers tested by a reliable institute, nor does the NBC or fire department insist on such a test and a certificate to that effect.
There is only one institute in India, CBRI Roorkee (Central Building Research Institute), which has a testing facility for a fire damper as per Clause 10 of UL 555 – 1995 (UL or Underwriters Laboratories is an American organisation) but other tests required by UL for a fire damper under UL 555 and UL 555S for leakage ratings of smoke dampers, are just not available. See details of various tests required by UL Standards.
CBRI, Roorkee carries out a Fire Endurance Test and a Hose Stream Evaluation Test, as per details below:
[top]
Under this test the specimen is subjected to standard heating conditions in a furnace which can run through out the evalution period at atmospheric pressure . The damper assembly is exposed to fire to conform to a standard time-temperature pattern as given below :
| Time (min.) | Furnace Temperature rise (°C) |
|---|---|
| 05 | 538 |
| 10 | 704 |
| 30 | 843 |
| 60 | 927 |
| 90 | 978 |
[top]
|
Extract from letter of Delhi Fire Service for a hotel in New Delhi Air conditioning The following must be ensured in respect of the air-conditioning system :
In kitchen extract ducts for pans & fryers shall be independent of any other work or any obstruction. Pans & fryers shall be provided with lid. Grilling and frying equipments in use shall not leave unattended. Main electrical switches and gas stop codes in a kitchen shall be positioned on an exit route and shall be clearly marked / labelled. The mechanism for pressurising the staircase, shaft lift, lift lobby / corridor shall be so installed that the same shall be operated automatically and also with manual operation facilities, when the automatic fire detection/fire alarm system or sprinkler system actuate. Extract from letter of Mumbai Fire Dept. for a hotel in Mumbai AC system
|
Two UL standards provide the basis for testing, qualifying, and rating Fire
Smoke Dampers. These two UL Standards are :
UL 555 Fire Dampers
UL 555S Leakage Rated (Smoke) Dampers for Use in Smoke Control Systems
Here is a summary of the major tests required to qualify dampers to these standards:
Dampers are exposed to a standard test fire for a period of either 1½ or 3 hours. This standard test fire is controlled to follow the time temperature curve illustrated. Immediately after conclusion of this fire test, the dampers are subjected to a high pressure hose stream test during which water, at a nozzle pressure of 30 psi for 1½ hour dampers and 45 psi for 3 hour dampers, is applied to the dampers from a distance of 20 ft. The hose stream test provides an extreme shock that ensures the dampers are structurally strong enough to withstand the rigors of the severest fire conditions.
[top]
Fire Smoke Dampers intended for operation by gravity or spring force (not driven by an actuator) must be cycled open and closed 250 times. Fire Smoke Dampers that are driven by an electric or pneumatic actuator must be cycled open and closed (by their actuator) 20,000 times. If the Fire Smoke Damper is also intended for use as a volume control damper, it must be cycled open and closed (by its modulating actuator) 100,000 times. These operational cycling tests are accomplished prior to the temperature degradation and leakage tests (described below) and ensure that the damper will function reliably after repeated operations.
A damper sample is exposed to salt spray in a test chamber for a period of
120 hours. After this exposure, the damper must close (and latch if a latch
is provided). This test demonstrates a damper’s ability to function after
a more severe fouling than the damper is likely to experience during its
intended application.
A damper is subjected to airflows and pressures and must demonstrate its ability to operate in the manner expected by its configuration and intended application. Smoke Damper and Combination Fire Smoke Damper actuators must operate the dampers open and closed three times and Combination Fire Smoke Dampers must also close as they would if their heat responsive device (RRL or fusible link) would operate. A damper model’s airflow velocity and differential pressure ratings are based on the velocity and pressure conditions against which the damper demonstrates its ability to operate.
A damper with an actuator that has previously been subjected to the Operational Reliability Cycle Test (described above) is exposed to an elevated temperature of 250°F minimum (or higher in multiples of 100°F) for a period of 30 minutes. After this 30 minutes exposure and while still at the elevated temperature, the damper actuator must operate the damper open and closed three times. Time of operation cannot exceed 75 seconds for any of the open or closed operations.
[top]
At least three damper sizes of each model being tested (minimum width by maximum height, maximum width by minimum height, and maximum width by maximum height) that have previously been subjected to both the Operational Reliability Cycle Test and the Temperature Degradation and Cycling Test must be tested for leakage. The minimum airflow and pressure ratings of dampers shall be 2000 fpm and 4 in. w.g. Ratings shall be set in 1000 fpm increments from the minimum airflow and in 2 in. w.g. increments from the minimum pressure. Leakage testing must be conducted at 400 fpm higher than the rated airflow and 0.5 in. w.g. higher than the rated pressure. A damper’s leakage rating is based on the worst case performance of the three damper sizes tested.
A jet of water is applied to the exposed face of the fire damper and any change in the gap between the various flaps is observed. The curve shown above also indicates the maximum gap noted in the damper blades at different times of the test in downstream position. Also indicated on the curve is the reduction of gap in case of one blade from 15 mm to 12 mm after application of Hose Stream. Basically this test is done to test the structural capability of the fire damper.
Since the safety of life and property, in any occupied building that is air conditioned, is vitally important, it would be desirable if industry (manufacturers of fire and smoke dampers) would initiate a dialogue with CBRI to undertake the remaining tests required by UL Standards, with part finance coming from industry and part from the Government by way of grants. Equally important, is that until such an industry initiative takes place and all test facilities are in place, specifiers and contractors take some basic precautions, such as insisting on CBRI tests and approval, as existing today, and installation practises in line with international standards.
[top]
