Defence research group QinetiQ is leading the way in a system which can detect fires hidden on board ships – before they have even started.

The system is based on smart sensors which are built to detect a single compound or gas, and which can be linked to recognise the mix of gases which indicate equipment is overheating and could burst into flames.

The initiative is just one strand in QinetiQ’s cutting-edge Fire Research Capability programme, part of the Environmental Sciences Business Group, as outlined by Fire Research Project Manager Linda Knutsen, who is based at the Haslar Marine Technology Park in Gosport.

One of the main areas of work for the seven-strong group of scientists is fire detection – both early warning and after a fire is believed to have been extinguished.

High-voltage and electronic cabinets on ships have been identified as a particular area of risk.

Linda said that the majority of fires are spotted by crew members, not machines, as existing detection systems can malfunction and are sometimes switched off to escape incessant false alarms – a practice which is not tolerated on Royal Navy ships.

With the trend towards lean-manning in both Naval and commercial ships, it could be some time before the smoke triggers an alarm or the problem is spotted by a member of the crew, so a system which warns of overheating in these cabinets before a fire breaks out would be a huge advance in safety.

The problem is that existing sensors are either not sensitive enough, or can be triggered by any number of false readings, so the QinetiQ team looked at the alternatives – one of which is an array of conducting polymer sensors acting like sensitive electronic noses.

Each of these tiny devices is essentially a polymer strip which connects two gold micro-electrodes. The polymer strip can be fabricated to react to the presence of an individual compound or gas, which will alter its conductivity and thus change the resistance between the electrodes, triggering a signal.

“We can link up four of the sensors for four different compounds which have been identified as precursors of a fire in an overheating cabinet,” said Linda.

“So if all four of them are activated then there is the risk of a fire. If just one – say acetic acid – is activated, then that might be because someone has just walked past with a bag of chips with vinegar on them.”

By linking them, the risk of a false alarm is therefore greatly reduced.

As these sensors are stable despite changes in temperature and humidity, have a low power requirement, and can be sensitised to a wide range of gases, they would seem to offer a relatively cheap and effective way of alerting a crew to a potential problem before fire breaks out.

The system could also be used in other areas, such as in the galley of a ship, or in other industries – a 21st century version of the miners’ canaries or the white mice which warned of poisonous petrol fumes on board the Navy’s first submarines.

Another flashpoint – in the literal sense of the word – is the timing of return into a compartment affected by fire, and this is another area which the QinetiQ team is tackling with promising results.

The current practice in the Royal Navy is to starve a serious fire of oxygen by closing all doors and hatches to the affected compartment, and then waiting for several hours, testing surrounding bulkheads for falling temperatures.

The Navy gave QinetiQ a wish-list of criteria, including the ability to test conditions in a compartment from outside, that the system is one-man portable, that it can warn if the fire is still alight or there is the risk of flashback, and that it can be linked back to the command centre.

QinetiQ have come up with the Fire Out Gas Detector, a briefcase-sized prototype which is based around a series of gas sensors sampling the atmosphere for carbon dioxide, oxygen, carbon monoxide, hydrochloric acid and flammable gases.

Air from the compartment is sampled through a narrow, extendable probe – which also contains a thermocouple to record the temperature – and the machine not only checks for the presence of gases, but also for the rates of change of gas levels. All this data is recorded for later analysis.

Using the combined sensor readings, a computer works out the level of danger and generates an appropriate warning, from all-clear to danger of flashback.

An active infra-red camera can also be deployed, producing a clear image of any fire, even obscured by reflections of the flames, in the compartment.

The use of sensors to increase the safety of ship’s companies has been extensively trialled on Navy warships, including aircraft carriers, Type 22 and Type 23 frigates and Type 42 destroyers.

Another strand of QinetiQ’s research has been carried out in conjunction with the US Defense Department and NASA, and is investigating the replacement of the gas halon in fire extinguishers.

The Montreal Protocol requires the replacement of the gas, which damages the upper levels of the Earth’s atmosphere, and there are high hopes for ‘Agent 873’, which has a shorter life in the atmosphere and is rendered harmless before it rises past the troposphere.

Linda said there was a possibility that the product could be on the market within two years, and that other commercial spin-offs from the department’s research programme could follow.