LAST month, the Japanese fire brigade tested its latest firefighting machine near a dam on the outskirts of Tokyo. The new tender has no ladder, uses one rigid, short hose to direct its jet of water and carries a crew of only two. Yet the machine is designed to tackle blazes that are beyond the reach of conventional fire engines.
The National Fire Agency鈥檚 new toy is a firefighting helicopter, and by the end of this year it should be ready to tackle fires in the highest Tokyo skyscrapers. What is more, when a major earthquake strikes, the Japanese fire service may use an entire fleet of these helicopters to reach blazes that are inaccessible to conventional fire engines.
The story behind the firefighting helicopter began in August 1989 when a TV set caught fire in a Tokyo flat. The occupants were away for the day and the fire spread quickly throughout the 24th floor of the 28-storey building. Neighbours raised the alarm and 30 fire engines raced to the scene.
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But the firefighters had a problem. Their ladders were not long enough to reach the source of the flames. And since the lifts could not be used, they had to climb 20 flights of stairs carrying breathing equipment and first-aid gear.
Like most high-rise buildings in Tokyo, the block of flats was fitted with an elaborate system of pipes and pumps, allowing water to be pumped into the system from a fire engine outside, and then through internal pipes up to the tenth floor. From there, the building鈥檚 own pump took the water the rest of the way to an outlet on the 24th floor. The system worked, but it was a difficult and dangerous process, and five people鈥攊ncluding a fireman鈥� were injured in the blaze.
Burning issue
When he read about the fire a few days later, Nobuyuki Souma knew there had to be a better system. From his office on the third floor of the National Fire Agency headquarters, he looks out across the East Garden of the Imperial Palace and at the high-rise buildings that surround it. In the fifty years since Tokyo was virtually destroyed by Allied bombing, the city has become a complex jumble of crowded buildings linked by narrow streets. Just the year before, a survey of the tallest buildings had shown that 355 skyscrapers were beyond the reach of the ladders fitted to fire engines.
鈥淚 thought the best solution would be a firefighting helicopter,鈥� says Souma, 鈥渂ut I knew there would be problems. Wind conditions are very dangerous around high-rise buildings, and the helicopter would have to get close enough to direct water at the source of the fire.鈥�
Neither was this a new idea. More than thirty years ago, the National Fire Agency studied whether helicopters could be used to dump water directly onto burning buildings from above. But the agency decided that the technique was flawed because the roof would block direct access to the source of the fire and the research was abandoned in 1968.
But Souma, who is in charge of operations planning at the National Fire Agency, decided to test a new technique: using a helicopter to hover alongside a building and shoot water horizontally at the source of the fire. In 1991, he persuaded the National Fire Agency and the Tokyo Metropolitan Government to develop his idea. With a budget of 拢1.6 million, he turned to Shigeru Saito, an engineer at the Flight Research Division of the National Aerospace Laboratory (NAL) in Tokyo, with a plan to modify one of the Fire Agency鈥檚 Super Puma helicopter.
Saito designed an onboard tank which could hold around 1.2 tonnes of water. He included a pump to fill and empty the tank that could work at a rate of up to 1200 litres per minute. With a 10-metre pipe hanging from its belly, the helicopter could refill in around 60 seconds while hovering above a lake or river.
The problem with directing water horizontally towards a fire is that the downdraught from the main rotors deflects the stream. So Saito added a boom that swings out from a frame beneath the fuselage and a rigid, extendible hose. Together these give a 10-metre reach beyond the heaviest downdraughts.
But the biggest challenge is flying such a machine. Aiming a jet of water at a window that may be smaller than 2 metres square is not easy at the best of times. But in a real fire, the pilot would have to cope with turbulent winds while maintaining a distance of at least 20 metres from the building. 鈥淭his leaves a safety margin for the rotor blades which are 7 metres long,鈥� says Saito.
To make matters worse, the pilot must also compensate for the changing forces on the craft. Since every action has an equal and opposite reaction, pumping the water towards the fire forces the helicopter away from it and possibly towards other nearby buildings. And as water flows out of the tank, the helicopter鈥檚 weight changes by more than a tonne in less than two minutes.
To test whether a pilot could cope with these conditions, Saito programmed the NAL鈥檚 flight simulator to replicate a flight in a firefighting helicopter. In 1994 and 1995, he invited the Fire Agency鈥檚 top pilots to test it out. 鈥淭he most difficult thing about designing the simulator was the wind patterns,鈥� says Saito. To build a computer model of the turbulence, Saito took measurements of the wind speed around a real building in a variety of weather conditions. He discovered that on the windward side of a building, the air currents are generally smooth. 鈥淏ut on the lee side you can get dangerous turbulence,鈥� he says.
Dangerous crosswinds
In addition, enginners at NAL developed a method for simulating the effects of sudden increases in wind speed. These gusts can cause dangerous vortexes near the corners of buildings and Saito believes they may play an important role in the hovering characteristics of firefighting helicopters. 鈥淔or the flight simulator, this kind of gust can be added to the general wind at random,鈥� he says.
During the simulated flights, the pilots had to aim the water jet at a predetermined spot on a building while maintaining the position and attitude of helicopter. The pilots thought that coping with the changing forces in the simulator was easy, says Saito. 鈥淏ut they weren鈥檛 testing this under real conditions.鈥�
To get a more accurate idea of the pilots鈥� ability to handle turbulence, Saito began flight testing with a real but unmodified helicopter in light winds. The task this time was to aim a searchlight at a 2-metre-square window on the 14th floor of a real building while hovering 20 metres away. Saito discovered that at wind speeds of under 4 metres per second, the pilots could hit the window with an accuracy of 80 per cent. And this was with a fixed boom although, in practice, a second crew member would operate the boom allowing the pilot to concentrate on flying.
Saito and the pilots also decided that the helicopter was safest when hovering with its side facing to the building and its nose facing into the wind. This would also maintain visibility by keeping the helicopter out of heavy smoke. And they found that the turbulence on the lee side was unpredictable and should be avoided. As long as these rules are observed, Saito believes that the helicopter could tackle blazes in moderate breezes of up to 7 metres per second.
Test flight
With the tests complete, the agency decided to convert one of its Super Puma helicopters for firefighting. On a sunny day in March at a disused aerodrome west of Tokyo, the fire agency demonstrated its new helicopter in public for the first time. Last month, it began more detailed flight testing to determine more accurately the changing forces on the helicopter as it discharges water and to allow pilots to refine the hovering technique. Later this year, they will go on to test this technique near a real building.
But some observers are sceptical about how well the helicopters will cope. Louis Picaud, the Tokyo representative of Eurocopter, which makes Super Pumas, says that a real fire in a skyscraper is likely to be much more difficult to tackle. The burning building may be surrounded by others, making access perilous and a side-on position with the nose into the wind impossible. Saito acknowledges that his results are only valid for an individual building. In a real city, the wind patterns around many closely spaced buildings may be far more complex. 鈥淎 real fire might not be in a single building on its own. And the helicopter might have to go a long way to refill with water,鈥� adds Picaud.
But despite his scepticism, Picaud says the craft could be used to tackle fires that have spread over large areas where fire engines cannot gain access. 鈥淎nd unlike the kind of firefighting aeroplanes we have in Europe, with this you can direct the water exactly where you need it,鈥� he admits.
Other uses have come to light since the helicopter idea was conceived. The fire agency was given a grim demonstration of the limitations of conventional fire engines when a massive earthquake hit the port city of Kobe in January 1995鈥攂y coincidence during the middle of Saito鈥檚 tests. With Kobe鈥檚 streets obstructed and water pipes broken, entire blocks of buildings burned out of control because fire engines were stranded on the outskirts of the city or unable to find a reliable water supply.
Hiroyuki Kamikura, who heads the fire agency鈥檚 fire suppression section, says that in such a situation the helicopter could stop fires from spreading and give rescuers more time to reach survivors. And since time is crucial, the fact that an unmodified Super Puma can be transformed in just three hours becomes important. This is much faster than it took fire engines to reach some areas of Kobe.
If it works well, Japan may not be the only country to take an interest. In January, a fire broke out on the top floor of one of Britain鈥檚 tallest buildings, the 42-storey NatWest tower in the heart of the City of London. Although controlling fires in tall buildings is a routine procedure, it can still be a difficult and dangerous task. Perhaps a firefighting helicopter could have made it easier.
