By Eamonn Ryan
In the design and construction of buildings and structures, the preservation of life and prevention of injury due to fire are the most critical considerations – apart from minimising damage to the structure itself.
Approaches taken to mitigate fires in buildings are multi-faceted, and include active measures such as smoke detectors, fire alarms, sprinkler systems, smoke extraction and evacuation protocols. Passive measures include fire containment through fire-resistant walls, roofs, floors and the installation of fire doors, along with clear signage to show accessible fire escape routes.
Fire engineering starts with looking at the most probable fire scenarios – for instance, Karel Roodt, director and engineer at The Fire Engineer, points out that it serves no purpose in a steel manufacturing warehouse to have a fire protection system dependent on sprinklers because there is nothing that can burn. The sprinkler system could end up creating more damage to sensitive equipment.
An important component of fire engineering is to prevent the spread of fire within a building. By containing the fire, further damage to the building is prevented while minimising the heat build-up and deadly smoke emissions.
Fire engineering is not just about designing a sprinkler system, or a smoke detector system: it involves looking holistically at the unique fire requirements of each premises. “For this reason, legislation requires that a building’s fire system be designed by an ECSA qualified fire engineer, of which there are two types: a fire system installation engineer and a fire safety engineer who designs the safety process.” The differences are spelled out in greater detail below.
When planning a concept engineered fire suppression system, numerous aspects are taken into consideration: life safety, systems effectiveness based on the combustible product (i.e., fire load) and processes, business continuity, building protection, environmental impact and cost. A cold store or food production facility is likely to undergo severe damage by a sprinkler system using water – a clean agent could be a possible solution but extremely costly – and therefore a perfect fit for an engineered system looking at a hypoxic system for cold rooms.
Fire dampers save lives by reducing the risk of smoke and of fire spreading through a building when disaster strikes. Its attraction is that it is fitted with a fusible link that shuts off the damper whenever the temperature at the damper rises above 72°C, says Christiaan Bosch, MD of Rickard Air Diffusion.
The damper can also be fitted with a motor that allows the building management system to control smoke and fresh air movement in a building during different stages of a fire. Keeping smoke away from the areas with no fire and extracting smoke from areas that had a fire can save lives.
“Even when there isn’t a fire, you can use it to control the amount of air allowed through the duct as a form of volume or pressure control. A fire damper is a product built of quite thick steel compared to other damper products, ensuring the damper can withstand fire for some time and protecting the occupants of the building from smoke and fire – though its purpose is not to put out the fire. It has been SABS tested to resist fire for two hours,” says Bosch.
He describes such a system as being appropriate to any building where the air conditioning is centrally located, or any system where air is distributed to different parts of the building. “Fire dampers are needed wherever the air moves through a firewall, partitioning the building into different fire sections, so that it can be cut off from the rest of the building to reduce the risk of a fire spreading.
“While steel fire dampers are cost effective, they are more expensive than normal pressure control dampers, as they have to be more robust to withstand the heat of the fire and they incorporate an automatic shutdown system.
“There are different systems, some that prevent fires and others that aim to stop fires from spreading. Fire dampers are typically used in conjunction with other systems being appropriate to certain types of applications such as various sensors, sprinklers and control systems. It’s the integration of these different systems that make for a safe building,” he notes.
The core function of a fire damper is to close down the ducting whenever the heat of a fire reaches 72°C in the duct – ranking as a substantial fire. “These automatic shutdown systems cannot be electronic, or they could burn out, but fire dampers rather use a fusible link that melts at that temperature, bypassing all electronic systems and snapping shut.”
“Our fire dampers are tested to comply with SANS 193:2013. The safety regulations in South Africa are good, and if the building owners employ consultants to design HVAC and fire systems to the relevant standards, building owners will own a safe building and occupants have the best chance of surviving if things go wrong,” explains Bosch.
He notes that in Europe there are a number of innovations using different materials that aim at extending the time that a fire damper will survive in a severe fire. “These do increase the cost of the system, while our standards in South Africa remain quite effective for performing this function. I believe in the future there will be more focus on electronic systems that detect fires early and rather reduce the risk of fires starting or spreading in the first place.”
Installation errors are rare. “The system is installed in line with the ducting by the mechanical contractor that installs the air conditioning system. A mistake that could be made is to install it the wrong way around. The fusible link has to be installed facing the direction from which the air is entering. This is unlikely if a reputable contractor is used,” says Bosch.
THE FIRE ENGINEER
Karel Roodt, director and engineer at The Fire Engineer, lists the three basic essentials of fire protection:
- Study of fire: To learn the causes of fire, fire extinguishing techniques, detection and extinguishing equipment and their uses, and the rules and regulations related to building construction
- Active fire protection: Includes manual or automatic detection of fire, the use of fire and smoke alarms, fire suppression, firefighting, and first aid firefighting
- Passive fire protection: Design of building and infrastructures, use of fire resistant material in construction, provision of isolating fire, fire walls and doors, smoke doors, signage, markings, and evacuation plans
“Even with the most comprehensive fire safety provisions that modern technology can provide, it is essential that there be adequate management of fire safety to ensure that the occupants of a building or facility reach a place of safety in the event of fire and to avert disaster. In many multi-fatality disasters and business losses, poor fire safety management has been found to be a significant contributing factor,” says Roodt.
EXTINCTION OF THE FIRE
Roodt explains that to stop a combustion reaction, one of the three elements of the fire-triangle (heat, fuel and oxygen) has to be removed. “Without sufficient heat, a fire cannot begin, and it cannot continue. Heat can be removed by the application of a substance which reduces the amount of heat available to the fire reaction. This is often water, which absorbs heat for a phase change from water to steam. Introducing sufficient quantities and types of powder or gas in the flame reduces the amount of heat available for the fire reaction in the same manner. Scraping embers from a burning structure also removes the heat source. Turning off the electricity in an electrical fire removes the ignition source.
Without fuel, a fire will stop. Fuel can be removed naturally, as where the fire has consumed all the burnable fuel, or manually, by mechanically or chemically removing the fuel from the fire.
The fire stops because a lower concentration of fuel vapor in the flame leads to a decrease in energy release and a lower temperature. Removing the fuel thereby decreases the heat.
“Without sufficient oxygen, a fire cannot begin and it cannot continue. With a decreased oxygen concentration, the combustion process slows. Oxygen can be denied to a fire using a carbon dioxide fire extinguisher, a fire blanket or water.”
ROLE OF WATER IN FIREFIGHTING
“Water can have two different roles. In the case of a solid combustible, the solid fuel produces pyrolysing products under the influence of heat, commonly radiation. This process is halted by the application of water, since water is more easily evaporated than the fuel is pyrolysed. Thereby energy is removed from the fuel surface, and it is cooled, and the pyrolysis is stopped, removing the fuel supply to the flames. In firefighting, this is referred to as surface cooling.
“In the gas phase, that is in the flames or in the smoke, the combustible cannot be separated from the oxidiser, and the only possible action consists of cooling down. In this case, water droplets are evaporated in the gas phase, thereby lowering the temperature and adding water vapour making the gas mixture non-combustible. This requires droplets of a size less than about 0.2 mm. In firefighting, this is referred to as gas cooling or smoke cooling,” says Roodt.
“Cases also exist where the ignition factor is not the activation energy. For example, a smoke explosion is a violent combustion of unburned gases contained in the smoke created by a sudden fresh air input (oxidiser input). The interval in which an air andgas mix can burn is limited by the explosive limits of the air. This interval can be very small (kerosene) or large (acetylene).”
He notes that water cannot be used on certain type of fires:
- Fires where live electricity is present – as water conducts electricity it presents an electrocution hazard.
- Hydrocarbon fires – as it will only spread the fire because of the difference in density and hydrophobicity. For example, adding water to a fire with an oil source will cause the oil to spread, since oil and water do not mix.
- Metal fires – as these fires produce huge amounts of energy (up to 7.550 calories per kilogram [a figure which is sometimes disputed] for aluminium) and water can also create violent chemical reactions with burning metal (possibly even serving as an additional oxidising agent).
“Since these reactions are well understood, it has been possible to create specific water additives which will allow a better heat absorption with a higher density than water, carrying free radical catchers on the fire, carrying foaming agents to enable water to stay on the surface of a liquid fire and prevent gas release, and carrying specific reactives which will react and change the nature of the burning material.”
Water additives are generally designed to be effective on several categories of fires (class A + class B or even class A + class B + class F), meaning a better global performance and usability of a single extinguisher on many different types of fires (or fires that involve several different classes of materials).
PASSIVE VS ACTIVE FIRE PROTECTION
Roodt describes Passive Fire Protection (PFP) as a group of systems that compartmentalise a building through the use of fire-resistance rated walls and floors. “Compartmentalising your building into smaller sections helps to slow or prevent the spread of fire or smoke from one room to the next. PFP helps to limit the amount of damage done to a building and provides its occupants more time for evacuation. PFP includes fire and smoke dampers, fire doors, and fire walls and floors. Dampers are used to prevent the spread of fire and smoke throughout the building through its ductwork. Fire doors help to compartmentalise a building. Firestopping helps to separate the building into compartments. Photoluminescent egress path markers help light the way to safety.
“Most warehouses are a disaster waiting to happen. Of the nine fire risk assessments I have recently done, all had glaring system failures. In one insurance case for fire that I have been consulting on, a risk assessment was done one week before the fire – which found no risk – yet the building burned down within a single minute,” says Roodt.
Components of such a system include:
- Fire-resistance rated walls
- Fire-resistant glass
- Fire-resistance rated floors
- Occupancy separations
- Division separations
- Tenancy separations
- Closures (fire dampers)
- Fire stops
- Cable coating
- Spray fire proofing
- Fireproofing cladding
Active Fire Protection (AFP) is a group of systems that require some amount of action or motion in order to work efficiently in the event of a fire. “Actions may be manually operated like a fire extinguisher, or automatic like a sprinkler, but either way they require some amount of action. AFP includes fire and smoke alarm systems, sprinkler systems, and fire extinguishers as well as firefighters. Fire and smoke alarm systems are used to detect whether there is fire and smoke in a building. Sprinkler systems are used to help slow the growth of the fire. Fire extinguishers and firefighters are used to help put out the fire altogether.
Its component parts include:
- Manual suppression
- Automatic fire suppression
- Fire detection system
- Hypoxic air fire prevention
“An AFP system takes action in helping to put out the fire but may not always function the way they are designed to work. Sprinklers could fail due to the lack of maintenance, water supply problems like frozen pipes, or even inadequate water pressure. On the other hand, PFP uses systems that help control and prevent the spread of fire and smoke. It does not, however, take any type of action such as putting out the fire. Therefore, both AFP and PFP are meant to work together during a fire, not one in place of the other. Both active and passive fire protection systems can control fires. Together they help protect lives and business continuity,” he adds.
POTENTIAL MISTAKES IN INSTALLATION
“It’s always a good idea to start with a concept design with schematic and P&IDs to do a QA on the system and go through the design taking into consideration safety, maintenance complexities and buildability during the construction period. I have seen many engineers who skip this process ending up with major items not included. A peer-review process by making use of the review services from another experienced engineer at concept stage already improves the design and minimises mistakes,” says Roodt.
“Operational and maintenance documentation and drawings are vital for the maintenance team to ensure fire systems are always ready. A majority of devastating fires are typically due to the failure of proper maintenance of the fire systems, and this is often the responsibility not of the fire engineer but the management of the company. Insurers have been becoming stricter in recent years in checking such maintenance, as well as insisting they install adequate sprinkler protection – due to the number of claims they pay out. On the downside, insurers tend to appoint professionals for their fire risk assessments who only look at SANS10400 compliance, which is simply inadequate for more complex cold room facilities for which a lot of newer research has been done due to their unique fire protection requirements.