Thanks to its extraordinary fire resistant properties, Nomex is reputed to have saved up to 5,000 people from death or critical injury. Keith Howard reports on a synthetic superhero
To the post-war generation, duped into believing that drip-dry bri-nylon shirts were a neat idea, the phrase 'man-made fibre' has an inglorious ring to it. But if you look beyond that unhappy example (sweaty oxters and static to shame a Van der Graff generator) it's undeniable that synthetic textiles represent one of the most significant technological developments of the second half of the 20th century.
Kevlar is the best known of the synthetic fibres to have had an impact on motorsport, although in many applications it has been forced to give best to carbon (graphite) fibre — weight for weight, an even stronger, stiffer alternative. Nomex, an aramid synthetic related to Kevlar, enjoys an altogether lower public profile but can justifiably claim that this is in inverse proportion to its true significance. Just ask the 5000-odd people in motor racing it is estimated to have saved from death or serious injury.
Like its cousin, Kevlar, Nomex is a product of the mighty Du Pont corporation. First synthesised at the company's Richmond, Virginia plant in 1965, it entered small-scale production shortly thereafter. Although its mechanical properties are pretty good, Nomex's most significant feature is its stubborn resistance to burning. As well as being self-extinguishing, it merely chars when heated to 350deg C or beyond — it does not melt. Moreover, it can easily be woven into a flexible cloth, thereby making it the ideal material from which to fabricate practicable fire-resistant clothing.
Nomex's rapid introduction to the American race scene — it was first worn at the 1967 Indianapolis 500, by every Goodyear driver — came about because of a personal friendship between astronaut Pete Conrad and Bill Simpson, who in 1958 started a motorsport supply business, at first making braking 'chutes for dragsters. Conrad (who was killed in a motorcycling accident last year) raced a Formula Vee at the time and in 1966 suggested to Simpson that he check out a new material being used for the canopies of Gemini programme re-entry parachutes. Simpson himself had been experimenting with a fire-resistant race suit made from aluminised twill cotton and it was, in his own words, "just awful".
Nomex, the new material being used by NASA, had been selected because of its fire resistance and Conrad reckoned it might be ideal for racewear. A few years later it would also be used in the space suits which Apollo astronauts wore to the moon.
Conrad persuaded NASA to let Simpson have a small amount of the Nomex cloth — at the time Du Pont was manufacturing a mere 10,000lb of the fibre a year, with a plan to increase this to 25,000lb, so it was like gold dust — which he duly made up into a race suit. Simpson showed it to Dan Gurney who liked what he saw of the new material, particularly when it was doused in fuel and set alight as a demonstration. Very soon Du Pont found it had a market for Nomex it had never envisaged.
Today the company makes around a thousand times the amount it originally intended, for use in numerous applications many of which count fire resistance as a primary requirement.
In the motor racing context Nomex also serves as the reinforcing fibre used in the honeycomb cores of sandwich composite panels, where in addition to its exceptional fire resistance it has the benefit of high electrical resistivity, the latter obviating the galvanic corrosion that can occur between carbonfibre skins and an aluminium core. (As an aside, this also explains the widespread use of titanium fittings with carbon-fibre composites. Even more corrosion resistant than stainless steel, titanium is uniquely immune from the oxidation from which other metals suffer when used in contact with the electrically conductive carbon fibre.)
Fire resistant clothing, however, remains Nomex's principal claim to fame. Asked to recall the most telling example of the life-saving difference it has made in motorsport, Bill Simpson — whose company has since grown into one of the premier racewear suppliers in the US — recalls the pit fire which occurred during an Indycar race a Michigan Speedway in 1979. It was an incident that makes the infamous Benetton Formula One pit fire of 1994 seem minor by comparison. Over 250 gallons of alcohol fuel gushed down the pit lane, engulfing around 30 people in the ensuing blaze. Happily every last one of them was wearing Nomex and none was seriously injured.
The single flaw with Nomex as it was originally manufactured was that it lost strength when exposed to intense heat, with the result that it could sometimes tear. In 1975 Du Pont addressed this problem by blending Nomex with a small amount (5 per cent) of Kevlar to produce Nomex III — one of a series of variants to have been developed down the years. As well as Nomex III the list now includes pure Nomex Delta FF, whose fine fibre particularly suits it to use in underwear and balaclavas, and Nomex DeltaA, DeltaC and DeltaT, all of which are mixed with different proportions of other fibres to adapt them to specific uses.
To test its ongoing Nomex developments, Du Pont has even built a rather gruesome device it calls 'Thermo-Man' — a full-sized human dummy which can be dressed in protective clothing before being exposed to a carefully controlled propane flash fire. Over 120 sensors distributed over the dummy's surface measure local temperature inside the clothing and allow the researchers to estimate the severity of burning that would have occurred had a real person been involved.
Less than 40 years ago F1 drivers were still going to work in impregnated cotton race suits which Bill Simpson politely describes as 'marginally flame retardant'. Today's F1 pilots, and those in many lower formulae too, are clothed from head to toe in Nomex and as a result are very much less likely to suffer burns in the increasingly unlikely event of a fuel fire. The late Pete Conrad will be remembered by the world at large for being commander of Apollo 12 and the third person to walk on the moon — but many in motor racing have equal cause to salute him for that timely conversation he had in 1966.