Neil Harrison of APL, a supplier of extinguishing systems fitted to mass storage systems, who took part in the first series of tests reported on in the article ‘Safe storage’ in this issue of FSE, gives his view about the implications of the tests. He puts the test into the context of a wider variety of storage applications.
The major problem in protecting storage machines from a total flood point of view is the fact that they are designed to afford easy access in use, so are not sufficiently enclosed to hold extinguishants for long. This is especially so with the larger machines, where leakage is generally greater. But when APL was initially requested to participate in fire extinguishing testing on a storage machine, we jumped at the chance and supplied and installed the various systems to be tested.
The storage machine in question was tested in the open air on a very cold November late afternoon. We installed an optical smoke detector, which was not connected to the extinguishing system, inside the top of the machine, and our Firetrace tubing was inserted from the middle of the machine from one side and along the top only. Firetrace consists of tubing which is designed to rupture at a certain temperature and release extinguishing gas. The were essentially three tests: two local applications protecting the motor and electronic compartment respectively; and one total flood system for the whole machine.
The first test involved placing a tray of flammable liquid below the electrical motor. The smoke detector operated in six seconds and the fire was extinguished in less than 20 seconds. The second test consisted of setting light to a small plastic bag of combustible material placed in an electrical compartment. Again, the smoke detector activated almost immediately and the fire was extinguished in less than 10 seconds.
The third test involved a section being cut out of the middle of the machine to allow the lighting of the combustible package, the opening then being covered by a black perspex plate (we were not allowed to install any detection tubing within the vicinity of this area.) This was an indirect application, where the extinguishant is discharged through pipework and diffusers after the rupture of the Firetrace tubing. As the only way a fire could start at this point would be by instantaneous combustion – either by spillage of chemicals or overheating outside the machine – we would normally have installed additional detection to protect such risks.
When the fire was started the optical smoke detector operated in a few seconds. It then became apparent that although the heat was building up in the middle of the machine, the smoke was creating a barrier that prevented sufficient heat from reaching the detection tubing. So when eventually the tubing ruptured (at the entrance point on the side of the machine) the CO2 discharge made no real impact on the fire, due to the excessive heat in the middle of the machine.
Useful lessons
Although the testing was very stringent and some of the tests posed difficulties in achieving the desired results, we are grateful for the opportunity to have taken part. It has benefited us considerably in our research and development in supplying systems to meet the various requirements for these types of storage machine.
APL also installs aspirating detection systems as an early warning, either individually within each machine or throughout the general area, or both. There is also the option of DetExt F/F total flood and local application systems, the system decided on by what is stored within the machine, where the machine is installed and, of course, cost.
The other major factor is whether you want to protect the contents of the machine from fire starting inside the machine at potentially hazardous points e.g. the electrical motors or electrical/electronic compartments, or from fire starting outside the machine for a period of time (until the sprinklers operate or the fire brigade arrives). This is where extended inertion can be beneficial. The other point to remember is that the choice of system and agent should be made according to the level and type of risk being protected.
Our total flood system (normally CO2) is designed to discharge into the machine with sufficient gas at a reduced rate. This allows for the concentration of CO2 to be kept inside the machine for a period of time without causing any damage by over pressurising the unit. The DetExt F/F system also gives the option of having extended discharge capability supplied in 30 minute increments. Most of these storage systems are in themselves unoccupied areas but lock-off devices and safety features are added for total flood applications.
A local application system in the machine’s electrical/electronic compartments is installed as standard. This is a standalone system complete with pressure switch, and will activate on overheating – without discharging the main total flood system.
New approach
Since these tests were carried out, we now install smoke detection as part of the local application, and double knock on total flood systems. In most of the latter cases, installing an optical smoke detector and a combined rate-of-rise and fixed temperature heat detector prevents a spurious discharge caused by smoke that could have entered the machine by accident – for example from someone burning rubbish outside.
The local application system uses a low pressure gas, such as Fe36, Fm200 or Novec1230. The cylinder is mounted inside the machine and the Firetrace tubing is attached to the motor and installed within the machine’s electrical/electronic compartments. In the event of overheating, the tubing ruptures at that specific point and discharges the gas directly at the source of overheating or flame. The system pressure switch can activate to operate a local alarm, building alarm, or to shut off power. Should the storage machines be stocked with non-combustible materials, we would suggest that DetExt F/F smoke detection and local application system would be the most sensible and cost effective solution.
We can also install what we consider to be the ultimate in fire prevention, the Wagner Oxyreduct system. Such systems work by reducing the level of oxygen so that a flame cannot be ignited or sustained. This can be installed inside a single machine, in a number of machines or inside the whole warehouse or room. An aspirating system is normally installed as an integral part of the system as – even though it is impossible to have a flame – a warning of smoke or overheating would be useful in raising an alarm and shutting off power, so minimising damage.
Neil Harrison is managing director of APL
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