Fires in traffic tunnels, though rare, are devastating and deadly. The Channel Tunnel fire in 1996, the Nihonzaka tunnel fire in 1979, the Kings Cross underground station fire in 1987 and others have shown that such fires burn long and hot. Indeed, the March 24 fire in the Mont Blanc tunnel connecting France and Italy burned for two days and killed 31 people.

In each of these cases, the fire was far worse than any risk assessment had predicted, inflicting damage on the concrete walls that required months of closure and cost millions in repairs and economic losses. For example, when fire burned for 10 hours in the 31-mile tunnel connecting France and England in 1996, the concrete walls peeled away layer by layer like an onion, destroying entire portions of the 18-inch-thick concrete ring.

Now, a researcher at the Massachusetts Institute of Technology believes that he understands exactly what happens to concrete in extreme heat, a first step to designing more fire-resistant concrete.

In two papers in the May issue of the Journal of Engineering Mechanics, Franz-Josef Ulm and colleagues analyzed the failure of tunnel walls, examining the mechanical properties of concrete at the molecular level and creating a computer model to mimic the material's reaction to intense heat.

"We used an interdisciplinary approach to this problem," said Ulm, a professor of civil and environmental engineering. "Using chemistry and mechanics, we considered the mechanisms at the scale of a few water molecules to explain what happens to a 45cm [thick] tunnel ring during fire."

The scientists discovered that when mature dried concrete is exposed to extreme heat for long periods of time, the chemical bonds between the water molecules in the concrete break, destroying molecular bridges that bind together the various materials which make up concrete.

As the water molecules are pulled out through deyhdration, the concrete loses its cohesion and weakens, pushing pieces of the concrete off the tunnel walls in very thin layers resembling onion peel. This phenomenon, called spalling, can eventually work its way through the entire concrete ring lining a tunnel.

"After the fire, there were pieces of the spalled concrete on the tunnel floor. You could actually see the aggregates in the material in these thin slices," Ulm said.

One possible solution to the spalling problem is to include tiny plastic fibers in the concrete mixture. When heated, the plastic would melt and reduce the risk of spalling. Another answer could be to use certain paints or coatings on the concrete.

Concrete buildings receive ratings indicating how long the structure can withstand fire. For instance, a Class 60 building can withstand 60 minutes of fire; a Class 90 building, 90 minutes. These ratings don't apply to concrete in tunnels, because the tunnel acts like a convection oven, drawing air in to fuel the fire. In tunnels, very hot temperatures last much longer. The air temperature during the Chunnel fire reached more than 1,000degreesf, heating the concrete to nearly 1,300degreesf.

Ulm pointed out that the United States hasn't seen a big tunnel fire like those in Europe, but it's not impossible. Subway tunnels generally include sprinkler systems, giving them a tremendous advantage over long underground or underwater traffic and rail tunnels.

Those longer tunnels are usually equipped with modern information technology that monitors traffic, providing safeguards against fire and swift communication when it does occur. But these systems can fail, as they did in the Mont Blanc and English Channel tunnels.

Studies detail fire's environmental impact Science magazine has published two research studies showing how fire affects the natural world.

The first study by the U.S. Geological Survey reviewed California wildfire records to 1910. The study revealed that the frequency of fires and the amount of land burned hasn't changed significantly, and the size of fires hasn't increased. This seems to contradict earlier research that the efforts to control wildfires have made them worse when they do occur because of the accumulation of brush.

The second study by U.S. and Brazilian researchers discovered that fires in the Amazonian rainforest had become so common that almost 50% of the remaining forest has burned to some extent. The study concluded that the current rate of fire would lead to the eventual transition of large areas of the rain forest to scrub or grassland.

The studies appeared in the June 11 issue of Science.

Non-flammable plastic may make safer planes Recent aircraft safety research has developed new polymers that are much more fire-resistant than the plastic materials currently used to upholster and adorn aircraft cabins. When heated, some of the new substances actually produce water vapor and leave a nearly non-flammable residue.

The findings, reported in March at the national meeting of the American Chemical Society in Anaheim, Calif., could help prevent some of the deaths in "survivable" airplane accidents.

The new materials could also help retard in-flight fires, which sometimes begin in the cargo hold, electronic compartments under the flight deck, lavatory or galley. Although rare, the consequences of an uncontrollable in-flight fire are great, as attested by the 110 fatalities in the Valujet accident on May 11, 1996.

The polymer research conducted at the University of Massachusetts-Amherst and the Federal Aviation Administration is part of continuing research into new fire-resistant polymers, sponsored by a government and industry consortium created to improve aircraft safety.

"If you look around in an aircraft, most of what you see is not metal, it's polymeric - the walls, the bins, the seats, the windows, just about everything except the chair supports," said lead author Phillip Westmoreland, professor of chemical engineering, umass-Amherst. Although polymers don't actually burn, they do decompose from heat, and many of them produce gases that burn.

The primary concern is the spread of the fire into the aircraft, the effect of burning interior materials on passenger evacuation and the creation of untenable conditions. The primary design goals to enhance post-crash fire survivability are meant to provide additional time for passengers to escape, increasing the evacuation rate.

"Forty percent of fatalities in impact-survivable accidents [for large transport aircraft operated by domestic carriers] are due to fire," said co-researcher Richard Lyon, faa program manager for fire research and fire safety in Atlantic City, N.J..

According to the faa, about half of the total deaths in passenger airline accidents occur in non-survivable crashes. The other 50% of deaths occur in what are generally considered impact-survivable accidents, such as runway collisions that ignite spilled fuel.

Two new experimental techniques, requiring only milligrams of material, were developed by the researchers to measure the combustibility of the new polyhydroxyamide polymer, known as pha. Testing showed pha decomposed very little in contrast to other polymers.

The pha that did decompose was converted to water vapor and polybenzoxazole, another nearly non-flammable polymer. "Quantum molecular modeling established how the decomposition gave water and a different type of solid polymer, pbo, that is extremely fire-resistant," said Westmoreland.

Why not just start with pbo instead of pha? "You can't start with pbo because it is too hard to make into useful products, such as fabrics or panels," said Westmoreland. "pha is a 'smart' fire-safe material. It can be made and processed by mild 'green chemistry' processes, yet when subjected to fire dangers, it converts into strong, stable pbo."

The new testing techniques are also useful for other materials, because they make it possible to test very small samples efficiently, thereby reducing the need to spend time and money producing large amounts of material for analysis. The key to this study's success, said the researchers, is the integrated approach of polymer synthesis, flammability testing and molecular modeling.

pha has potential applications beyond aircraft, such as turnout gear for fire and rescue crews. Already, the Army Materiel Division in Natick, Mass., has a three-year crash program to come up with more fire-safe clothing for military uniforms.

A European researcher has found a species of beetle that may be able to sniff out forest fires, doing for firefighters what bloodhounds have done for trackers.

Stefan Schutz of the Justus Liebig University in Giessen, Germany, writing with colleagues in the March 25 issue of Nature, reported that adult jewel beetles can detect a burning tree up to 50 miles away. The Buprestidae beetles of the genus Melanophila are able to do this because they lay their eggs only in the wood of trees freshly killed by fire.

The adult beetles of both sexes meet at the site of the fire, often mating while the fire is still burning. The beetles detect fires and orient to them by means of an infrared organ situated on the thorax next to the coxae at the middle legs. One infrared organ houses about 70 sensilla.

This research is the first step in perhaps finding a way to harness this unique talent to help protect forests, or even buildings, from fire. It found that the antennae of jewel beetles can detect substances in smoke emitted from burning wood. In fact, Schutz and his colleagues have shown that the antennae of jewel beetles contain exquisitely sensitive sensors that detect very specific chemicals found in smoke, in concentrations as low as a few parts per billion.

Researchers coupled a standard flame-ionization detector, which detects compounds released in smoke, with an "electroantennographic detector," in which the amputated antennae of beetles are hooked up to detection equipment. This set-up essentially records what beetles are smelling from the insects' own standpoint, giving an exact reading of the beetles' capabilities.

The beetles are even thought to be able to distinguish between different chemicals, so that they can locate the distinctive chemical signature of a favorite species of tree. For example, the researchers estimate that the beetles' sensors are so exact that, from a kilometer away, they can detect a single pine tree, 30 centimeters in diameter, with bark smoldering to a height of two meters and a depth of one centimeter, releasing about seven grams of a smoke-derived substance called guaiacol per hour into a light breeze.

The equipment used by the researchers - improved artificial noses for the specific detection of a range of airborne particles - is as accurate as the beetles and may, in fact, find its own way into fire detection schemes.

Current firefighter communication devices have many limitations. Radios are easily damaged by water or foam agents. Multiple channels can lead to confusion finding the proper frequency during emergency operations. Gloved hands limit manual dexterity. Facepieces and fireground commotion conspire to distort or cover audio transmission.

All that may be about to change as a new device edges closer to being marketed. Fire chiefs attending last year's Metropolitan Fire Chiefs Conference in San Diego witnessed the demonstration of a prototype microphone that could change field communications. Coastal Systems Station, a research and development activity of Dahlgren Division, Naval Surface Warfare Center, has entered into a licensing agreement with Sensory Devices Inc., New Eagle, Pa., for commercialization of the microphone.

What's different about this microphone is that firefighters don't need to speak into anything. In fact, it's not even positioned near the mouth. It's worn where the helmet liner presses against the forehead so it can pick up the skull vibrations caused when speaking. Those vibrations are then transformed into electric signals that are fed into the firefighter's radio transmitter.

The demo in San Diego was dramatic. As 120 chiefs listened, a fire company posted outside the conference hall started up a pumper, chain saw and other equipment, creating 110db of noise four floors below. In the midst of this cacophony, a firefighter spoke into a standard 800mhz vhf radio, transmitting above to the conference. The communication, amplified for the assembled chiefs, was unintelligible.

The firefighter then changed to a helmet outfitted with the head-contact microphone. Suddenly, everything said in the racket on the street was completely understood. All agreed that the device was a significant improvement over conventional radios with lapel mikes.

First developed for use by Navy Seals during Operation Desert Storm, the head-contact mike eliminates most of the background noise that forces firefighters to shout into conventional mikes. Plus, it works whether or not a firefighter is wearing an oxygen mask.

The microphone was created by Frank Downs, a Navy inventor so prolific that the Seals call him "Q," after the character who builds the fanciful spy-ware used by James Bond. Perhaps best of all, Downs thinks it should be possible to produce the microphone for "a couple of hundred dollars."

The microphone technology grew out of a 1995 Pittsburgh firefighting tragedy, in which a captain and two firefighters were trapped in the basement of a burning house when the stairs collapsed. All three perished when their oxygen ran out. Even though they had two radios with them, none of their communications were received.

The connection between the Navy commandos and Pittsburgh firefighters is a former civil engineer named Robert Saba. Like many others, Saba, 66, of Glenshaw, Pa., watched the televised funeral of the three firefighters the morning of Feb. 18, 1995. "I couldn't help wondering if there was something we could do," he recalled.

Saba, who had just come out of retirement to work for the Mid-Atlantic Technology Applications Center at the University of Pittsburgh, contacted Pittsburgh Fire Chief Charlie Dickinson and suggested that nasa technology might prevent another such tragedy. mtac works to entice private businesses to make use of such technology.

As a result, in April 1996, the Pittsburgh Fire Bureau, nasa's Langley Research Center and mtac joined forces to form the Fire Fighting Task Force, which has a charter to locate and apply advanced, affordable technologies to enhance firefighting safety.

The work of the fftf represents a new approach of federal laboratories joining together to address specific public needs. In terms of firefighting, fftf intends to investigate technologies appropriate for such areas as communications, monitoring/tracking, enhanced visibility tools, apparatus, environmental monitoring and protective clothing.