Introduction
Effective smoke management is an essential component of fire safety because the flame is not the only danger in case of ignition. Specifically, smoke can reduce visibility, involving toxic gases, or be unbearably hot. Considering this, it is essential to ensure that people have little to no contact with it while escaping a burning building. The paper describes and analyzes the existing ways to enable a safe evacuation in the event of a fire.
Types of Control Systems
Fire and smoke control systems target to reduce the threat to human life as well as the possible damage to property in an emergency. The principle of their work lies in controlling the movement of smoke within a building so that it is possible to anticipate and prevent its spread (“Fire and smoke control,” n.d.). One of the purposes is to protect people who are inside the building while they are evacuating and provide them with sufficient time to do that successfully (O’Connor, 2021). In addition, it is critical to ensure that firefighting personnel has access to the setting “without suffering smoke-related injuries or complications” (IFSEC Global, 2022, p. 2). Therefore, smoke control solutions should be integral to the life safety systems that both residential and non-residential buildings have. The construction of a building determines the type of smoke control system that will be the most relevant in it because the effectiveness of control depends on the organization of space.
The two basic approaches to smoke management, each of which incorporates several solutions and techniques, are passive and active. The systems of the former kind do not utilize any mechanical equipment and mostly involve physical barriers to fire and smoke, such as curtains (“Active vs. passive smoke management,” n.d.). Therefore, they are possible to refer to as smoke containment systems; their function is to localize fire and smoke to prevent those from spreading to the paths of egress. Natural extraction systems, which are based on the physical buoyancy of hot smoke rather than any mechanical force, belong to passive as well. In fact, their construction and functioning principles are similar to the configuration of a regular fireplace chimney.
The operation of active smoke control systems, meanwhile, presupposes exhaust by means of mechanical equipment. One of the most popular techniques this category includes is pressurization; as apparent from its name, it lies in creating and maintaining a pressure difference between rooms (Cosma, Hughes and Nigro, 2020). Specifically, the pressure in the path of egress, such as the stairwell, must be higher in comparison with the adjacent premises, so that smoke cannot infiltrate into it (“Smoke management,” 2018). To add to the effectiveness of this method, it may be helpful to depressurize the neighboring spaces, such as corridors, increasing the difference (Wittasek and Gumpertz, 2019). Another subtype of the active smoke control system is mechanical ventilation, which enables exhausting smoke from the affected areas substantially faster in comparison with natural.
Advantages and Disadvantages
Ideally, buildings should have both types of smoke management systems in parallel. In such a case, they complement each other, which reduces the risk of fatal failures (“Understanding the differences,” n.d.). Notably, passive systems, including doors, curtains, and other possible smoke baffles, are simple to install and use but have quite a limited capacity. They interfere with the spread of smoke, providing the occupants with time to escape but not necessarily remove it from the building quickly. Their active equivalents can do that, but the mechanisms or moving parts that they involve “often mean room for malfunction or error” (ibid, para. 19). Simply stated, active systems may become partly or completely inoperative, which will lead to leaving people in danger. Therefore, it is the most reasonable to install both types throughout the building to optimize smoke management.
ASET/RSET Analysis
As apparent from the above, the essential function of smoke control systems lies in ensuring that the occupants are in tenable conditions while escaping the building. The ability of management systems to maintain those conditions, meanwhile, is limited even in case of combining several types, even though such a decision maximizes it. Therefore, the time it takes to egress in the event of a fire should be as short as possible to reduce the risks.
In fact, however, navigation may be challenging, especially within new buildings, which frequently include one or several atria, large spaces that unite multiple floors. Another disadvantage of modern architecture is the insufficient amounts of vertical egress paths (Cosma et al., 2020). The combination of these two factors can lead to situations where large groups of people find themselves on upper floors with poor access to stairs, which is outstandingly threatening. Considering this, safety engineers must adjust smoke control systems to the above peculiarities to protect people as appropriate.
The latter requires a thorough analysis of the characteristics a certain building has. The critical parameters to measure are the available safe egress time (ASET) and the required safe egress time (RSET). The former stands for the period between the beginning of a fire and the moment when the conditions become untenable due to smoke, heat, and toxic gases (“ASET/RSET analysis,” n.d.). How soon this happens depends strongly on the configuration of a particular building, specifically materials, ceiling heat, the geometry of the premises, the presence of physical barriers, ventilation, and others (“ASET vs. RSET,” n.d.). Therefore, the most reliable way to identify the available safe egress time is fire modeling, which should occur directly in the building to ensure the practical applicability of its outcomes.
Regarding the RSET, it means the time that safe evacuation of all occupants after a fire signal actually takes. A precise identification of this parameter calls for examining the building as well; specifically, it is a sum of the alarm time, the evacuation delay time, and the movement time (“ASET vs. RSET,” n.d). The first is the period it takes to inform the occupants about the fire through the present alarm system, automatic or manual.
The second is the time that passes before they start evacuating, for which reason it is frequently referred to as the pre-movement time. Its main determinant is not the number of people but the activities they perform because the list of belongings to gather depends on these (ibid). In practice, the evacuation delay time may vary between several seconds and a few minutes based on the occupancy of a specific building.
Finally, the movement time is the actual duration of the walk to safety after the gathering. The amount of accessible exists, such as doorways and staircases, their pass-through capacity, and the average walking speed are the aspects that factor into it (“ASET vs. RSET,” n.d). In addition, safety engineers should consider the possibility of disorganized human behavior in panic or despair, which can prolong both pre-movement and movement periods.
As apparent from the above, safe evacuation is possible exclusively on the condition that ASET exceeds RSET. To ensure this, measuring each of the mentioned points is critical in which the ASET/RSET analysis lies. Notably, modeling the spread of fire in particular premises provides the understanding of which passive and active control systems are necessary to interfere with the movement of smoke and heat.
Tenability Criteria
For additional clarity, it would be relevant to specify which conditions can classify as tenable or untenable. As said, the factors of danger other than flame are smoke, toxic gases, and heat; tenability, therefore, is inversely related to their presence (Shawash, 2018). Specifically, neither the temperature nor the level of toxicity should bear a threat to human life, and smoke should not reduce the visibility of evacuation routes.
More precisely, the temperature in the areas that do not lie directly above the flame has to remain below 60°C. The minimally acceptable visibility equals 10 meters (Shawash, 2018, para. 6, 9). For small rooms that are possible to leave quickly, 5 meters and up to 100°C may be tolerable. Regarding toxicity, many models for calculating it exists; the main criterion is the materials that are burning because their capacity for gas production may vary substantially depending on their chemical composition.
Guidance on Smoke Control
Another nuance to consider when organizing smoke control throughout common escape roots is the driving forces of smoke movement. One of those is the innate buoyancy of smoke, which can make it infiltrate into the adjacent rooms. The probability of this apparently is the highest in modern apartment buildings, as they frequently have a form of atriums, that is, include large spaces and few built-in enclosures. Installing smoke barriers, therefore, is among the essential fire safety measures for which atriums call (The British Standards Institution, 2017). Another requirement is the presence of natural ventilation that enables the exhaustion of smoke due to the so-called stack effect (O’Connor, 2021). The latter, as well as buoyancy, in fact, is the force that determines the operation of passive smoke management systems.
Regarding active smoke control, it is based predominantly on the above technique of pressurization, which helps interfere with the expansion of smoke. Similar to any gas substance, the latter can occupy all of the available space due to its volatility, which is worth mentioning among the forces responsible for its movement. Creating zones of higher pressure, however, allows for an invisible barrier to infiltration by increasing the density of the environment (“Smoke management,” n.d.). Therefore, pressurizing corridors and staircases used for evacuation is a quite reliable method of providing tenable conditions during it. In addition, each stairway should have a separate system of mechanical ventilation (HM Government, 2019). This enables the maximally rapid exhaustion of smoke in case it does migrate to the evacuation route.
Conclusion
To summarize, smoke bears a substantial threat to occupants in case a fire occurs, for which reason it is essential to ensure that they are able to egress safely. The primary measure is to interfere with the spread of smoke, which its volatility and buoyancy enable. This is possible to do with or without the use of mechanical equipment; the second variant presupposes physical barriers, such as doors or curtains and natural ventilation. The means of this kind are more reliable in comparison with machines due to the low, if any, probability of malfunction but dramatically less effective. Considering this, the most reasonable solutions in fire safety should involve both types of smoke control systems.
Reference List
Active vs. passive smoke management(n.d.).
ASET/RSET analysis (n.d.).
ASET vs RSET (n.d.).
The British Standards Institution (2017) Fire safety in the design, management and use of buildings – Code of practice. BSI Standards Limited
Cosma, G., Hughes, J. and Nigro, L. (2020) Smoke control for high rise buildings. SFPE Europe.
Fire and smoke control systems (n.d.).
HM Government (2019) Fire safety. Crown.
IFSEC Global (2022) Fire protection: Your complete guide to smoke control systems, regulations and building codes.
O’Connor, B. (2021) Smoke control systems.
Shawash, F. (2018) Calculating tenability conditions when smoke drops below 2m.
Smoke management(2018).
Understanding the differences between active vs. passive fire protection systems (n.d.).
Wittasek, N. B. and Gumpertz, S. (2019) Common smoke control approaches in high-rise buildings.