According to NFPA[1] surveys in the 1930s, the National Fire Insurance Organization suggested that dampers should be used in the HVAC system to prevent the passage of smoke, flames, and heat caused by fire. Since then, a large number of experts in fire science, efficiency and effectiveness of automatic closing of smoke and fire dampers as well as automatic shutdown of ventilation fans in the HVAC system in order to prevent the transfer of smoke, flame and heat to other areas of the building from the fire place. They have proven that they are far away. Nowadays, engineers use smoke and fire dampers in the design of fire systems in many modern buildings.
Fire damper standards
A fire damper is a device in an HVAC system that automatically closes upon detection of heat, according to UL555. A smoke damper is a device that is installed in order to control the movement of smoke in an HVAC system, according to the UL555s standard. Combined smoke/fire dampers: The performance of this equipment is such that they resist smoke and fire at the same time and meet the requirements of smoke and fire standards. In the United States, old standard codes also contain provisions to prevent smoke emissions in buildings. Some of these requirements include the installation of smoke dampers. The 2000 edition of the International Building Code has retained the requirements for installing fire-rated smoke dampers in corridor walls, similar to the old standards. But according to the new requirement that was added in the new edition of the IBC standard, it is allowed to have smoke dampers in the penetration of shafts, instead of using an automatic smoke control system.
While this change in the standard was approved in the IBC, according to many requirements of the old standards, if there is an automatic fire extinguishing system (sprinkler), the requirements of walls and sections with fire rating or resistance to Weakened or eliminated the smoke. Since the installation of smoke dampers at the entrance of the shafts is considered a new requirement in the standards, and despite considering the problem of smoke spreading throughout the buildings (including buildings with sprinklers), the requirements of smoke dampers in penetrating the ducts in the shaft, there are still objections in Smoke dampers are used in buildings. Opponents believe that the cost of installing and maintaining smoke dampers is imposed on the owners as an unacceptable cost, while it has no effect on increasing the safety of residents. In most cases, the reliability and effectiveness of sprinklers is used as a justification for removing the requirements of installing smoke dampers in shafts. The main members of the International Standards Association (ICC) consistently do not accept proposals that do not use smoke dampers at the entrance of the duct to the shaft.
Research results [2] AMCA
In 2008, the International Air Transport Control Association (AMCA) under contract with the Koffel Organization, compiled the authoritative research in this field for use in computer modeling. The results of this survey are divided into two important parts.
Absence of any acceptable evidence to justify the removal of smoke dampers at the entrance of the shafts. But in this research, a fire incident in the last 25 years has been mentioned, and in its report, the dangers caused by the spread of smoke for the residents have been discussed. Most fires in buildings occur in areas where people are present. Some of the old standards still do not require the use of smoke dampers, but the smoke caused by fire must be removed from the buildings, and for this purpose, these buildings must be equipped with smoke dampers.
In this research, a recent simulation as well as several tests with real dimensions for the vertical spread of smoke in a building through a shaft are also mentioned. More research was also done by Koffel company to show the importance of using smoke dampers in the sections where the channel enters the shafts of buildings with sprinklers.
Reliability of the sprinkler system
All objections to the use of smoke and fire dampers in order to save costs in buildings equipped with automatic sprinklers have two main aspects: 1- The reliability of the automatic sprinkler system. 2- The issue of relative cost / benefit. In all these cases, it is assumed that sprinkler systems are able to operate satisfactorily and at the right time during a fire. However, the possibility of a sprinkler system malfunction and turning a small, controllable fire into a disaster is still debatable.
In checking the reliability of sprinkler systems, they check the performance of the system without taking into account the possible cases of its failure, so many possibilities of system failure in performing tasks are not considered. In 2009, John Hall of NFPA published a report entitled; American experiences in using sprinklers and other automatic fire detection equipment; presented The information used in this report was collected in the period of 2006-2003. In this research, Hall says that automatic sprinklers are very efficient equipment in the fire protection system and in 95% of the cases that the system started working, the fire was big enough for the system to work. When the sprinkler system is activated, it has worked successfully in 96% of cases. Therefore, by combining effective performance and also assuming that the fire can be detected by the sprinkler system, firefighting operations have been successful in 91% of cases.
In 1997, an NFPA study was conducted to evaluate the spread of fire and smoke in buildings with and without sprinklers based on data collected from 1986 to 1995. This research showed that in high-rise buildings (seven floors and more), in 11.4 percent, in medium-height buildings (3 to 6 floors), 15.7 percent, and in buildings that were not equipped with sprinkler systems, in 34.4 percent, smoke. caused by the fire has led to casualties in higher floors.
Although this report does not have the ability to define the severity of the damage caused by the spread of smoke and toxic gases, the results show that many fires in buildings equipped with sprinklers have also injured people on the floors above the place of fire. . If the smoke dampers are removed in the buildings with sprinkler system and the automatic sprinkler system has a problem for any reason, the spread of smoke penetration during the fire will definitely increase.
It is important to point out that in the NFPA report, not only the elimination of smoke by the sprinkler system is not discussed, but it does not even state whether the smoke production will not continue after the fire is extinguished by the sprinkler. A research by G.W. Mullholland titled; Smoke production and its characteristics; In the 1995 SFPE Fire Protection Engineering Handbook, it was published that a person in an 1800 sq-ft room in which smoke particles from burning a sofa made of 9lb polyurethane were uniformly distributed would be able to see the hand. He himself will not be at a distance equal to the length of his hand. Even when the sprinkler can successfully contain the fire, the fire may continue and continue to produce suspended solids and toxic gases. A lot of research has been done on fires where the sprinkler water was blocked by obstacles and the water never reached the fire. In this situation, sprinkler system will be practically ineffective.
Experts confirm that the automatic sprinkler system is very efficient, even though it is not completely error-free. Sprinkler manufacturers and fire protection associations are constantly working to improve the reliability of these systems. John Klote, in an article titled; The division of spaces and dampers is fundamental; It states that, in the period when the use of buildings, raw materials, methods of construction and facade design are constantly changing, the possibility of new conditions and errors can be expected. For this reason, buildings equipped with sprinklers must also be equipped with other protection facilities so that in case of an error in sprinkler operation, the protection conditions of the building are still at an acceptable level.
In addition, damper manufacturers, contractors, installers and fire service companies are cooperating with each other to ensure proper operation of dampers, proper installation and periodic maintenance of dampers. Building standards can control the materials used in building construction that must be considered when designing a sprinkler system. But neither building standards nor designers can monitor the materials and equipment that residents bring into these buildings. As a result, if inappropriate materials enter the buildings, the sprinkler system may easily have problems. Therefore, it is better that sprinkler systems are supported by equipment such as smoke dampers to prevent the spread of smoke to other parts even if the fire is successfully extinguished by the sprinkler.
Conclusion
During a fire, the HVAC system can move the smoke to areas far away from the fire. However, there are still discussions about the best method for fire control in buildings equipped with and without sprinklers. For many years extinguishing the system was considered the standard approach to smoke control versus smoke movement to other areas.
Since 2000, according to the IBC standard, it is not necessary for the HVAC system to remain on in the smoke control mode for constructed buildings. Without the design of a smoke control system, or complete shutdown of the system and operation of smoke dampers in the shaft, the HVAC system will carry smoke throughout the building. Even shutting down the HVAC system without the presence of dampers cannot prevent the oxygen supply to the fire as well as smoke transfer throughout the building through the HVAC system.
Installing smoke dampers in the shafts can prevent the movement of smoke to other places through the air conditioning system.
[1] National Fire Protection Association
[2] Air Movement and Control Association
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