Tire Dealers Association of Canada Convention - Autosphere

tire Pyrolysis
Overheating Warning
Every year in Canada, numerous people are seriously injured or die due to a tire explosion caused by
a pyrolysis phenomenon, which is the chemical breakdown of the tire brought on by excessive heat.
Tire pyrolysis begins when the temperature of the rubber that goes into the production of the tire attains
± 250°C.
It then breaks down in a variety of chemical
substances, such as methane, hydrogen,
carbon black, and styrene. When
they make contact with the oxygen inside
the tire, these flammable vapours are set
ablaze by auto-ignition when the temperature
gets to ± 430ºC, bringing on an
explosion so powerful that debris can be
blown 300 metres away.
Origin of the explosion
A report based on expert examination
following a fatal work injury enumerates
the possible heat sources of this phenomenon:
• Overheating brakes
• Poor tire condition or over/
under tire inflation
• Using a blow torch on a
wheel or near the tire
• Welding on or near the wheel
• Automobile fire
• Contact with high-tension
power line or lightning
• Presence of contaminants
inside the tire
• Absorption of flammable
liquids by the tire
• Installing and uninstalling tires
Explanation of the phenomenon
When the vehicle is in motion, the tires
cool down thanks to the air circulating
at high speed. If an abnormal condition
occurs, causing the tires to overheat, the
cooling process is much less efficient when
38 Tire News tn October 2008
If you suspect unusual tire overheating,
it’s better to remain at a safe distance
until the tire has cooled down.
the vehicle is at a standstill, increasing the
risks of pyrolysis. The heat causes the air
inside the tires to dilate and significantly
increase their pressure, bringing about the
degradation and softening of the rubber.
If the tires are not cooled, the pyrolysis
phenomenon begins and an explosion can
occur at any moment within 24 hours.
Extreme caution
Whether you’re a truck driver, automotive
technician, or other, if you suspect that
a tire is unusually overheated, it’s better
to keep a safe distance for a reasonable
lapse of time until the tire has cooled. If
possible, measure the tire’s temperature
with an infrared temperature sensor; it
must be below 250°C. As soon as the situation
is favourable (temperature around
70°C), you must deflate the tire to a minimum
and carry out a careful inspection.
Good practices
The afore-mentioned enumeration of potentially
dangerous heat sources resulting
in pyrolysis must be a guide to be memorized
by you and your staff, and your work
processes must reflect this awareness in
order to avoid potential dangers.
Preventive training
François Charron
technoserv@sympatico.ca
According to numerous reports of serious
accidents involving tire pyrolysis, the dangers
linked to a tire blowout are overlooked
in the workplace. Truckers, suppliers,
and technicians must be made aware of
this phenomenon, which has caused the
loss of many lives in Canada. tn
This picture illustrates the brake actuator and the
threaded bar to be screwed to the end in order to
compress the diaphragm spring inside, thus releasing the
pressure on air brakes. Said rod is usually stored on the
side of the actuator. It’s the only good way of neutralizing
the pressure on brake shoes and preventing brakes from
overheating.
Translated from its original French by Marc-Alain Nantel.