Back to basics: a round-up of the main types of fire protection

This article aims to provide data centre managers with an overview of the main facts and options available. A logical starting point is a quick physics lesson: most of us will have been taught the causes of fire when at school, but here is a quick refresher.

Fire requires three elements for ignition: heat, fuel and an oxidising agent (typically oxygen). When any one of these three elements of the fire ‘triangle’ is removed, a fire can be prevented or extinguished. If that does not happen, then the fire will evolve to the next stage, known as combustion, which is the chemical reaction that feeds a fire more heat and allows it to continue. Most fire protection and suppression techniques are based on removing any one of the four components of the fire tetrahedron.

Traditionally, halon-based systems – which interrupt the chemical reaction of fire - were popular, but changes in legislation now make it very difficult for any data centre owner (or indeed, any business) to use these systems. While there are a few exceptions, it is generally prohibited to refill legacy halon systems, even with recovered, recycled or reclaimed halons.

Today, the majority of chemical fire suppressant systems are covered by the F-Gas regulations, which are designed to mitigate environmental impact.

While the phasing out of halon-based systems gave businesses the inconvenience of having to find alternatives, it did create a new impetus into the market, with vendors introducing a variety of systems based on different techniques, the main ones being water or water-based systems, chemical extinguishing agents (which both work by cooling the fire), inert gasses and hypoxic systems (both of which reduce oxygen).

Let’s examine the properties, pros and cons of each of these techniques and how they might apply to the data centre.

Water
Water systems vary according to droplet size, including misting systems. Water carries a strong ‘green’ card, because it has a relatively small impact on the environment and low toxicity (although contaminated water after a fire still has to be safely disposed of). However, it does have performance limitations, most notably the fact that it can cause electrical short-circuiting.

In data centres, where equipment typically has a high value, this is obviously not an ideal situation. Furthermore, water based systems cascade downwards as opposed to left or right, so if a data centre cabinet was on fire, then water may not be the most effective solution for the job.
Inert gasses

Inert gasses are generally mixtures of argon and nitrogen and work by removing oxygen from the environment being protected. Inert gasses have 30 seconds to administer the suppressant then two minutes to put out the fire. They can be very effective, but due to the elimination of oxygen, they are not suitable for areas where people may be present.

They are also toxic at the concentration level required to extinguish a fire and need high pressure to operate, typically 300 bar, compared to less than 50 for chemical extinguishing agents. This means that more onerous and thorough health and safety processes are required. A good reference for data centre owners is the Pressure Equipment Directive (PED).

Hypoxic systems
Hypoxic systems are extremely complex fire suppressions systems. Typically operated with the help of a microprocessor, they regulate the amount of oxygen within an environment to prevent combustion taking place. They divert nitrogen into a room and oxygen is then directed into the atmosphere. Hypoxic systems are also safe for humans, although careful monitoring is required, since levels of oxygen are reduced. Are there any downsides? For the data centre manager, a big factor to consider is that hypoxic systems do require significantly higher power consumption compared to other fire suppression method techniques. They may also require a greater degree of maintenance and expertise.

Chemical extinguishing agents
Last but not least, the other big category of fire suppression available today is chemical extinguishing agents. These work by removing the heat elements from the fire triangle, rather than removing oxygen. Legislation requires that the fire suppressant must be discharged within 10 seconds and the fire extinguished within 30 seconds thereafter, so chemical extinguishing agents act pretty quickly, good news for data centre managers.
Since they are not based on removing oxygen from the atmosphere, chemical extinguishing agents have a comparatively high margin of safety, so people have time to exit the building without having to compromise on the speed of fire suppression. Products vary according to manufacturer, but other benefits can include: zero ozone depletion potential; resistance to corrosion; electrical non-conductivity;, no remaining residue; and being safe for use on energised equipment, so that operations can be continued during a fire emergency.

Depending on the system chosen, they can be strapped to walls or pillars, so they take up a lot less valuable floor space in the data centre when compared to an inert gas system. There is also no need to have pressure or water tanks installed outside the data centre. Some systems can be refilled locally (as opposed to having to be taken off-site) which, given that many data centres are remotely located, makes maintenance simpler.

Conclusion
It pays to investigate the different types of chemical extinguishing agents available, because some have higher margins of safety than others; enable remote filling (which makes maintenance more simple) and variations in global warming potential or atmospheric lifetime (which fall within the F-Gas Regulations).

While chemical extinguishing agents may appear to be more expensive up-front compared to some alternatives, most data centre owners will be more concerned about ongoing cost-of-ownership, including maintenance and low power consumption compared to some of the other methods mentioned.

Plus, there is the over-riding priority to give people and valuable data centre equipment maximum protection, particularly since many data centre businesses are being asked to provide high business continuity. With such a range of advanced systems available, finding the most fit-for-purpose fire protection system is within the reach of any data centre manager.