DIESEL ENGINE RUNAWAY CAN HAVE FATAL CONSEQUENCES FOR COMPANIES INVOLVED IN MANUFACTURING, TRANSPORTING AND STORING HAZARDOUS MATERIAL

1. HCB MONTHLY | OCTOBER 2018
106
DIESEL ENGINE RUNAWAY is a dangerous
phenomenon where the running engine
draws extra energy from low concentrations
of any hydrocarbons in the surrounding air.
This causes uncontrolled overspeed beyond
the safe limits and an explosion or ignition
of the external air-fuel mixture.
A fatal accident at ICI Wilton in the UK in
1969 led to increased general awareness
of diesel engine runaway in the oil and gas
industry. Based on an Esso Research patented
original flow operated solution, Chalwyn
created its automatic D valve in 1972 to
overcome this problem. Esso Fawley refinery
required installation of these safety valves for
vehicles and machines working at the UK site.
BURNING ISSUE
Gasoline engines and diesel engines do not
operate the same way. A gasoline engine is
generally fed by a carburettor and butterfly
valve where the volume of air-fuel mixture
taken into the engine is controlled by the
accelerator pedal, which subsequently
controls engine speed.
A diesel engine’s speed, however, is
controlled by the air-fuel mixture happening
in the combustion chamber. Diesel engines
use a ‘direct injection’ method with no need
for butterfly valves to manage air flow.
Since no air restriction is present in a
diesel engine, it means that an unlimited
air supply is possible.
Diesel engine runaway can be caused
by several variables; however, one
common cause is the engine drawing in
external hydrocarbons that have leaked
into the atmosphere.
Accident history has shown that diesel
engines are a potential source of ignition
in areas processing oil and gas. Airborne
combustible hydrocarbons can blend with the
air causing an additional supply of energy that
is consumed by the running diesel engine.
Since diesel engines control fuel and not air,
the engine can no longer maintain speed
control and at surprisingly low concentrations
the extra energy is sufficient for the engine to
accelerate uncontrollably.
At higher than normal rpm speeds the typical
result is internal valve ‘float’ which exposes the
combustion flames into the manifolds and this
then ignites the outside flammable mixture with
catastrophic consequences.
Turning off the ignition key or fuel supply
will not stop this process and the engine will
continue to accelerate beyond the red line and
normal safe limits. Only fitting an emergency
shut off valve in the engines air intake system
will prevent the overspeed by stopping the
engine at a pre-set limit
CONSEQUENCES
Incidences of damage from diesel runaway by
consumption of the lubricating oil were seen
and understood in earlier times, but these
rarely resulted in loss of life. However, in the
late 20th century, accident investigations and
improved safety standards led to requirements
for automatic engine shutdown devices
STICK TO THE
SPEED LIMIT
COMBUSTION • DIESEL
ENGINE RUNAWAY CAN HAVE
FATAL CONSEQUENCES
FOR COMPANIES INVOLVED
IN MANUFACTURING,
TRANSPORTING AND STORING
HAZARDOUS MATERIAL

2. SAFETY 107
in several regions for offshore oil and gas
operations. Unfortunately, the awareness and
local regulations varied internationally, so
engine-related accidents have since continued
in both ‘upstream’ and ‘downstream’
petrochemical activities.
In Texas in 2003, two workers were killed
and two more were injured when a vapour
cloud from the cargo was drawn into the
intakes of two idling vacuum trucks. In 2005
a US refinery explosion was ignited by a
runaway diesel pickup; 15 people died and
170 were injured in the blast.
In 2010, an offshore rig explosion killed
eleven people and created the largest
accidental oil spill in history. A diesel engine
runaway in the engine room is considered
one of the main contributing factors.
THE SOLUTION
Most tanker trucks use diesel engines,
making this already dangerous problem into
an extremely dangerous one in the event of
a flammable liquid or gas leak. Loading and
unloading of flammable and combustible
liquids is one of the most hazardous
operations likely to be undertaken at any
manufacturing or storage facility. Tankers
transporting highly flammable liquids are a
top concern; diesel engine runaway can
cause explosions if not prevented.
In any instance, the drivers of these
vehicles are likely to be innocent victims of
an accident involving diesel engine runaway
and it is the fleet operator’s duty to make
sure all risks have been considered when
working in hazardous areas and all safety
precautions are in place.
With increased awareness has come
regulatory reform. Transport Canada has
taken a pro-active approach and passed a
new law that requires automatic air intake
shut-off devices to be fitted on all diesel
engines. Compliance with this law took effect
on 12 January 2018 and it is recommended
that operators review safety policies and
follow this leading example. HCB
www.chalwyn.com
“AIRBORNE
COMBUSTIBLE
HYDROCARBONS CAN
BLEND WITH AIR
CAUSING AN
ADDITIONAL SUPPLY
OF ENERGY”