Great rules of fire
July 1st 2009

The term 'machine' is a general one, so it's hardly surprising that fire risks, and the best methods for addressing them, vary from application to application. For this reason, the first step in providing effective dedicated fire protection is always to carefully analyse the functioning of the machine and to carry out a detailed risk assessment.

On the basis of the information that this provides, attention can then be focussed on the two principal areas of fire protection – detection and suppression.

Fire detection Among the many fire detection options that can be used with machines, one of the simplest and most versatile is the heat detector. These detectors trigger an alarm when a preset temperature is reached, which means that they can be easily matched to the operation of the machine.

For example, in a shrink-wrap machine, a temperature of 105ºC or so may be perfectly normal, so a heat detector set to operate 30ºC above this would be a good choice to provide a fire warning.

Heat detectors are, however, not always the best option. With some machines, such as those working with combustible or even explosive materials, a much faster response than a heat detector can provide is likely to be needed. For these, flame detectors may be more appropriate.

In some applications, smoke detectors are also worth considering, particularly where it is desirable to give general protection to a large machine. It is important to remember, however, that many machines emit fumes and vapours during their normal operation and, if disruptive false alarms are to be avoided, the detector chosen must be able to discriminate between these and real smoke from a fire.

The best option is usually a neural detector, which look at several characteristics of the smoke, and which can be fine-tuned to match the application and to minimise the risk of false alarms.

The location of the detector must also be considered carefully. Often it will be mounted on the machine, or immediately above it. In some instances, however, it may be necessary to mount the detector within the machine. A typical example is where the machine incorporates a substantial guard or cover. If the fire breaks out inside this, an external detector will be far too slow to respond, so a detector inside the guard or cover will be needed.

It is worth noting that it is not always necessary to fit an automatic detector. If staff are always present when the machine is operating, they will probably be the fastest and best fire detectors, so all that will be needed is a fire alert push-button or a manual break-glass alarm point.

Fire suppression The most frequent suppression choices for machine applications are water, water foam and carbon dioxide. All of these have benefits and shortcomings.

Water, for example, cools fires quickly and knocks down flames, but it is messy and can cause damage over and above that caused by the fire itself. Water is also incompatible with some types of fire, including those involving electrical equipment and also where reactive materials are included - such as magnesium - which might explode on contact with water when hot.

Foam is inexpensive and effective at smothering fires, but shares many of the disadvantages of water. Carbon dioxide, on the other hand, is a much cleaner extinguishing agent but care must be taken to ensure that it is used in such a way that it doesn't create a life safety hazard.

There may also be other factors that affect the design of the extinguishing system. The size or configuration of the machine may, for example, mean that localised extinguishant discharge is more practical than simply flooding the whole machine with the extinguishing agent.

As we've seen, the fire risks associated with machines are diverse and choosing the best way to address them in a particular application can be a demanding task. Nevertheless, such is the range of fire protection technologies available that an effective solution is invariably available.

Hopefully, this short article will have provided some useful pointers for developing such a solution but, particularly in complex or unusual applications, it is desirable to enlist the aid of a fire system supplier that has proven expertise in machine protection, and that can offer access to a full range of protection technologies.

Gavin Nielsen is part of Siemens Building Technologies Fire Safety department

More articles from Siemens Building Technologies Ltd: