快猫短视频

I鈥橫 CROUCHED, dripping wet, behind a metal barrier in a restricted area
of one of Britain鈥檚 most secure defence research labs. It鈥檚 pouring with rain
and, together with 35 others, I鈥檓 watching khaki-clad engineers running around
what looks like a rocket launch pad. The balloon is about to go up.

The balloon in question is a large rubber bag the size of a basketball,
suspended between three metal poles. It鈥檚 full of petrol and primed with a small
explosive charge. Detonating it will create a massive cloud of highly flammable
vapour that should ignite almost instantaneously. I鈥檓 looking forward to an
impressive demonstration of pyrotechnic dexterity. My heart thumping, I adjust
my ear defenders and wait for the bang.

This is the grand finale of a three-day workshop on firework chemistry hosted
by the Ministry of Defence at Fort Halstead in Kent. It takes place every couple
of years or so鈥攚henever organisers Ken and Bonnie Kosanke get time to
visit Britain from their pyrotechnics research lab on a ranch in Whitewater,
Colorado. Their pupils are a mixed bunch. Some are from the defence industry, a
few are in the firework business themselves, and there鈥檚 even a young engineer
about to begin a stint as a special-effects coordinator at Pinewood Studios.
They all have one thing in common, however: a burning passion for ear-blasting
air bombs and riotous Roman candles.

The tricks of the trade have changed remarkably little in hundreds of years.
The basic ingredients for a firework are fuel and oxygen in which to burn it.
During the first lecture, Ken fills us in on the best sources of oxygen: usually
salts such as ammonium nitrate or potassium perchlorate which contain three or
four oxygen atoms per molecule. Fuels include charcoal or metals such as
aluminium and magnesium. You can even use plain old sugar: heat a test tube of
oxygen-rich sodium chlorate, chuck in a single jellybaby and the tube will erupt
in a violent spurt of yellow flame. 鈥淚t usually leaves the room smelling like
candy floss,鈥� Ken tells us.

Most fireworks are a bit more sophisticated than that, of course. Add a pinch
of strontium salts, for example, and you can make flames burn crimson. A
teaspoon or two of titanium filings or auramine dye gives you added sparkle or
coloured smoke. To change the speed at which the stuff burns鈥攖o make
fireworks that either fizzle or bang鈥攜ou vary the ratio of fuel and
oxidiser. Over the centuries, chemists have discovered that they can create all
kinds of jaw-dropping pyrotechnic effects using anything from arsenic to dried
plant sap.

But pyrotechnics is getting seriously analytical. 鈥淚t used to be done like
cookery, from a recipe book, but times have changed,鈥� Ken says. Rather than
simply repeating tried-and-tested recipes, researchers are analysing exactly how
each chemical component affects the way a firework looks and sounds, as well as
addressing the safety issues.

Not that they鈥檝e solved every problem. Making blues and greens appear
brighter to the eye is still a nightmare. Chemists can add barium salts to
create green flames, and copper salts for blue. But these colours never seem
particularly bright. Part of the difficulty, Ken explains, is that many of the
other compounds added to pyrotechnic mixtures simply burn yellow. And since our
eyes are more sensitive to this colour, it tends to mask the more exotic blues
and greens.

Back at their ranch, the Kosankes spend some of their time trying to solve
problems like this. Occasionally they even run 鈥減yro-retreats鈥�, when they invite
a bunch of like-minded mates for a weekend to explore novel combinations of
chemicals. 鈥淭here鈥檚 no real plan,鈥� says Ken, 鈥渨e just mess around looking for
new effects.鈥�

To see how the professionals do it, Tony Cardell, the head of pyrotechnics at
Fort Halstead, takes us on a tour of his research labs after lunch. Each
building is designed so that the blast from any accidental explosion is
channelled upwards through the lightweight roof or outwards between flexible
wall panels. As we walk towards the labs, he points out a low building shrouded
in scaffolding. 鈥淲e lost a roof there last week,鈥� he says. The design obviously
works.

A huge robotic arm almost two metres tall dominates another lab. Its job is
to compress an explosive powder called magnesium Teflon Viton into cylindrical
pellets. MTV is nasty stuff. Squeeze it into blocks and light it and MTV burns
very hot鈥攁t about 2500 掳C鈥攕o it鈥檚 used in decoy flares designed
to draw heat-seeking missiles away from fighter jets. However, set fire to
loose, powdered MTV and the stuff detonates like a bomb. More dangerous still,
freshly prepared MTV has the unpleasant habit of going off spontaneously. Once
you鈥檝e made MTV, you should wait for nine-and-a-half minutes. If nothing bad
happens in that time, you can be reasonably sure it won鈥檛 explode. No one knows
why, Cardell says. And until they understand more, no one is volunteering to do
the robot鈥檚 job.

Human touch

But not everyone in the industry feels the need for robotics. Later, over
tea, I sit with Richard Diaper, a chemist at Chemring Countermeasures, a
Wiltshire-based company that manufactures signalling and decoy flares. Whenever
they make a new batch of compounds, he tells me, the material has to be tested
for its sensitivity to friction. Chemring has its own unique method. 鈥淚t鈥檚
called Marcus,鈥� Diaper says. Marcus bashes the stuff with a hammer. Apparently
the industry is teeming with technicians whose skill lies in wielding a hammer
time and time again with precisely the same force.

The following day, Ken tells us about the industry鈥檚 arch-enemy: smoke. It
ruins everyone鈥檚 fun, obscuring special effects and reducing the brightness of
colour. And when you gasp in awe at a display, you could be getting more than
you bargained for鈥攖he smoke particles are often poisonous.

It鈥檚 a particular problem with indoor fireworks. The pyrotechnics in shows
and concerts can be accompanied by thick blankets of noxious smoke, thanks to
the metal salts and chlorinated polymers used to create colourful effects.
Unless there鈥檚 adequate ventilation, an audience鈥檚 health may be put at risk.
But it鈥檚 the orchestra, actors and stage hands who get the worst of it. They
breathe in the stuff every day鈥攁nd twice on Saturdays.

Help is now at hand, however. At Los Alamos National Laboratory in New
Mexico, a research team has spent years developing low-smoke fireworks. Rather
than using traditional fuel and oxidiser, these rely on high-energy nitrogen
compounds that burn with virtually none of the smoke or ash of traditional
gunpowder fireworks.

The work sprang from research into military propellants and explosives
designed to produce a minimum of smoke. Then, a couple of years ago, chemists
Michael Hiskey, Darren Naud and David Chavez set up their own
business鈥攚orking outside Los Alamos office hours鈥攚ith the aim of
selling low-smoke fireworks to the public.

To make these fireworks affordable, they decided to use chemicals that they
could buy off-the-shelf, rather than the more exotic compounds they were
developing in the lab for the military. So they focused on
nitrocellulose鈥攏itric acid and cotton鈥攁 commercial propellant
commonly used in bullets. 鈥淚t鈥檚 cheap, available everywhere and it burns almost
as cleanly as the more complex stuff we make at work,鈥� Naud says.

With very little smoke to spoil the show, their fireworks produce intense
colours in a wide variety of hues. And they need just a fraction of the
dangerous metal salts that colour traditional fireworks. Most of the by-products
are harmless: mainly nitrogen, carbon dioxide and water.

Nitrocellulose isn鈥檛 perfect, however. To build fireworks, you need mixtures
that burn at different rates鈥攆ast-burning charges to propel rockets or
bursting shells high into the air, and slower-burning mixtures for fuses and
flares. Nitrocellulose only burns at one speed. With some secret chemical tweaks
they eventually solved this problem鈥攄espite suffering a major setback when
1999鈥檚 New Mexico forest fires sent all their chemicals up in smoke. But they
hope to begin shipping their 鈥済reen鈥� fireworks to distributors in the US and
Germany later this year.

By then, however, they could be up against some stiff competition鈥攆rom
their own work. The Walt Disney Corporation is currently negotiating with Los
Alamos for the rights to manufacture and use the smoke-free propellants that
Hiskey and his team created during office hours.

These products would be perfect for use in the massive displays that run
daily at most Disney attractions. Disney is a corporate pyromaniac: it even
employs researchers to push pyrotechnics to the limits. Its engineers have
developed a firework gun鈥攁 multi-barrelled monster controlled by computer
and powered by compressed air (see 鈥淪hooting stars鈥�).

Light fantastic

The 鈥渁ir-launcher鈥� achieves what pyrotechnicians have, until now, only
dreamed of. It spits shells hundreds of metres into the air with unparalleled
precision. And without the massive charges of gunpowder that conventional
launchers require, Disney鈥檚 new artillery creates far less smoke, which means
brighter colours and less pollution. So far, the air-launcher has been used to
create displays at the Epcot Center and Disneyland, Florida. But the high-tech
shells make it very expensive to use, and Disney has shelved plans to put it to
work around the world.

By the end of the course at Fort Halstead, I鈥檝e learned the economics of
pyrotechnics as well as the science: air-launched, pollution-free fireworks are
all very well, but they had better be cheap. We鈥檇 rather cough and splutter in
the toxic smoke than cough up for expensive, cleaner, brighter displays.

The saving grace of cheap fireworks is that people still love the thrill of
the bangs and flashes鈥攅ven if the colours aren鈥檛 all they might be. Out on
the firing range, we鈥檙e waiting in eager anticipation for the petrol balloon to
blow. After a few minutes there are three urgent blasts from a klaxon, and a
loudspeaker booms: 鈥淔iring Now鈥�. A heartbeat later it goes off. There鈥檚 a soggy
bang and the balloon dumps its petrol onto the already soaking ground. 鈥淚t鈥檚 too
damp,鈥� Cardell shouts cheerily.

We鈥檙e disappointed, but not for long. He orders an engineer to light a huge
Roman candle. It burns rapidly, spitting bright reds and greens high into the
air. After a while it disappears from view as the platform is shrouded by smoke.
We might be coughing and choking, but we鈥檙e inspired. I鈥檓 off home to make a
display for myself. Nothing too ambitious, though鈥攁nd if it doesn鈥檛 work,
who cares? I can always eat the jellybabies.

Disney engineers have found a way to light up the night with unrivalled
displays of colour. Their air-powered gun uses electronic fuses and a
computer-controlled aim to shoot bursting shells and coloured stars three times
as high鈥攁nd far more precisely鈥攖han old-fashioned fireworks.

Conventional aerial shells are launched from 鈥渕ortars鈥�, thick cardboard tubes
buried in the ground. Each mortar contains a charge of gunpowder which blasts
the shell into the sky. This explosion also lights a short length of fuse that鈥檚
connected to the shell鈥檚 main charge. The time the fuse takes to burn determines
the height at which the shell explodes.

But the air-launcher does away with the need for a mortar. Instead,
a burst of compressed air blows the shells skywards. You control the altitude
the shells reach by adjusting the air pressure.

Disney has redesigned the firework shell, replacing the short length of fuse
with a circuit on a small chip. This contains a timer and a detonator. Just
before firing, the computer controlling the air-launcher programs the delay into
the shell, the gun puffs the shell into the sky and moments later, on a command
from the circuit, the chip fires the detonator. The skies over the Magic Kingdom
have never looked so spectacular.