Choosing a fire extinguishing system – a best practice guide
Choosing and specifying the most appropriate fire extinguishing system for the right location can be a complex and often bewildering task. There’s probably never been more choice on the market, representing a variety of different approaches, plus there are an increasing number of variables to consider. These range from the obvious – lifetime costs, location, extinguishing efficiency – plus other growing pressures, particularly sustainability and environmental legislation. Not surprisingly, the process of identifying and evaluating fire extinguishing systems can quickly become downright confusing.
This article does not set out to recommend one type of system over another – after all, no two situations are the same and there is definitely no ‘one size fits all’ solution in this industry – instead, it aims to give readers an insight into the factors to consider and the type of questions they should be asking their suppliers.
Probably a good starting point is looking at how much the market has evolved in recent years, because for anyone who is replacing systems that have been in-situ for a while, it makes sense to carry out some research into those changes. It is common knowledge that halon was phased out some years ago, with the exception of some limited usage in the oil and gas sector, though this now has a sunset date too.
The phasing out of halon spurred the introduction of a host of alternatives and today, the main systems being used are aqueous or systems based on clean agents such as inert gas, HFCs or fluoroketones (FKs). These all have their relative pros and cons and rather than starting by looking at the type of system, it makes far more sense to analyse the specific requirements of each situation, starting with location.
Location and storage
The overall number of rooms to protect needs to be considered, but also the physical reach of a single system. Depending on the manufacturer, nozzle coverage and ceiling height reach will differ. Clean-agent systems using engineered agents have a smaller footprint than inert gas and water-based systems and, since the former can also now support pressure up to 50 bar, they can ‘throw’ the extinguishing fluid further (sometimes with a distance between bottle and nozzle being up to 100 metres straight). They are therefore able to support fire extinguishment in a larger and more remote area than previously possible. In turn, this means that fewer cylinders are needed.
Also, different types of system require different approaches to storage. Water and inert gas-based systems require a comparatively higher volume of storage, which may result in an increased floor load. Clean agent-based systems typically require less storage space and also have a smaller overall footprint.
Costs that are often forgotten in initial project calculations are additional construction costs: installing a fire system is not always just a case of wall-mounting a set of cylinders. For instance, inert gas-based systems always require installation of ‘over pressure’ exhaust systems, which can incur extra time and cost. Depending on the number and weight of cylinders being stored, flooring may also need to be reinforced.
Continuation of operation
When looking at the overall costs of a fire extinguishing system, it is tempting to consider just installation and maintenance and hopefully the chances of the system ever being discharged are slight. However, this risk does need to be factored in and, of course, there are instances of possible discharge. While the priority is on protecting human life and valuable equipment, clean-up costs should also be considered in systems that don’t use a clean extinguishing agent.
Among the main types of system in use today, discharge time varies from 10 seconds to more than two minutes. Clearly, the longer the time it takes to extinguish a fire, the better chance it has to take hold and thus cause damage. There is also the potential damage caused by the fire extinguishing system itself: inert gas and clean agent systems do not cause any damage and leave no perceptible residue, so sensitive electronics or other equipment are safe. However, inert gas systems can be hypoxic at the concentration required to extinguish a fire and this needs to be considered in situations where people may be present. Engineered agents, especially FKs, have a large margin of safety to people. Water-based systems are safe to human life, but can cause damage to equipment and require significant clean up.
The amount of downtime before a return to ‘business-as-usual’ also has cost implications. For instance, a 24/7 data centre will probably have a disaster recovery strategy and some form of back-up, but this would ideally be a last resort. With inert gas and clean agent systems, equipment can be re-energised within hours and workers can return to the site, whereas water-based systems will have a longer clean-up time.
Then there’s the requirement to refill bottles as quickly as possible and this is another variable. If that period is more than 72 hours, or the nearest refill facility more than 500km away, the system owner would probably have to install a back-up system, thereby increasing the overall investment cost. Systems that can be installed in-situ are therefore preferable, but it’s important to ensure that the material in question can be easily transported. For instance, FK is a fluid at room temperature and thus can be shipped via air, road or sea. Naturally, water-based systems have the same flexibility. Other agents such as inert gases and HFCs always need to be pressurised, so do not have this transport and in-situ refill flexibility.
Systems may be in place for years before they are replaced, so it is also important to consider ongoing maintenance costs. Apart from the frequency of service visits, plus pressure checks for inert gas-based systems, there are other less obvious factors to consider such as replacement of hoses and cylinders. Will systems/cylinders need to be taken off-site for refilling? Again, this raises the requirement to have back-up systems in place.
Sustainability and regulation
A final area to consider is sustainability. Systems that may be subject to regulatory restrictions in the future may need additional requirements under the international directives (namely the Montreal and Kyoto Protocols). For instance, HFCs used in fire extinguishing have been included in the latest version of the F-gas Regulation in Europe. With their zero ozone depletion and no impact on global warming, water-based, inerts and FK clean agent systems are not affected by any existing or anticipated environmental, health or safety legislation.
Clearly, there are multiple factors involved and no two situations will be the same. It therefore makes sense to carry out a thorough analysis of what is required and work with a system supplier with the necessary experience to advise on all facets of selecting, installing and owning fire extinguishing systems that will remain fit for purpose for years to come.
For more information, go to www.3m.eu/novec1230