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Phone: 541-352-7942
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C. M. CONSULTING
A Division of Cliff Mansfield Incorporated
ASPHALT PLANT SAFETY
Part 1
by
Cliff Mansfield
Asphalt plants can be very dangerous places.
Accidents, sometimes fatal, happen far too often. Most can be traced to the same
root cause: the need for production superseding common sense and normal safety
practices. The incidents that follow occurred in the western U.S. in a five year
period. Sadly, they were not the only ones.
CASE #1:
It was a little past seven o'clock in the morning. A long line of trucks waited
at the plant when the superintendent drove up. Numerous attempts to contact the
plant by radio had failed. If someone had asked him, the superintendent would
have admitted he was pretty steamed when he pulled into the yard and the plant
wasn't running. This particular asphalt plant operator had been late on several
other occasions, causing expensive delays.
The superintendent climbed the stairs to the batch plant's elevated, divorced
control house. It was empty. A trip into the switch room confirmed that none of
the starter circuit breakers were tripped and locked out. Out in the stockpile
area he could see the loader working the piles so he knew the loader man was
ready to go. As a recently promoted, ex-plant operator he knew that time was
money. He decided to get the plant running himself. A split second after
starting the pug-mill the superintendent knew his mistake. The pug's access door
was open. The fledgling asphalt plant operator, with less than six months on the
job, was in the pug tightening a loose shank. He was 22 years old, with a wife,
two kids and a long life out in front of him. The devastated superintendent took
early retirement.
Lockout-Tag Out
In this incident, poor training, operator error and management impatience are to
blame. There is no doubt that if the plant operator had locked out the pug-mill
circuit breaker that morning he would still be alive. Pug-mills and slat
conveyors are exceedingly dangerous and notoriously unforgiving to their
victims, yet nearly every accident involving them can be traced to that one
simple failing by the operator. Failure to follow LOCKOUT-TAG OUT procedures.
OSHA regulations require that the power source be disconnected, manually locked
out and tagged to prevent accidental start-up before any work is performed on a
piece of machinery. In this incident the operator failed to follow regulations,
resulting in his death.
Beyond that, another issue surfaces. The superintendent simply had no business
touching anything at the plant without first ascertaining the location of
everyone involved at the facility. He was as much at fault as the operator.
CASE #2:
In the southwest a few years back
an asphalt plant ground man was killed while using a propane torch to light the
main burner. The 'flame-eye' (a device that either confirms that the burner has
lit or shuts the fuel off if not) had failed a few days earlier and had been
by-passed. In an unrelated incident the ignition transformer for the igniter had
burned out. A new one had been ordered, but was several days away, so the ground
man had been using the torch regularly to fire the burner. On this occasion,
according to a witness, when the man pushed the torch into the burner air stream
it was blown out. The plant operator, distracted by a state inspector, kept his
finger on the 'start' button continually blowing atomized raw fuel into the
drier. The ground man, after some difficulty, managed to re-light the torch and
again pushed it into the air stream. This time the accumulated fuel ignited
explosively severely burning the ground man. He fell off the burner deck to the
ground, fracturing his skull. He later died as a result of his injuries.
CASE #3:
Another west coast plant suffered a catastrophic explosion and fire for similar
reasons in '94. Fortunately, no one was killed. Two unrelated events combined to
form a potentially lethal situation. Earlier in the week the plant, a
Caterpillar drummer with a baghouse, suffered generator problems which caused
the electrical frequency-- normally 60 cycles --to vary. This caused many
problems. Among other things, it affected the baghouse's internal temperature
sensors causing wildly inaccurate readings. These sensors control an air
solenoid which in turn controls the position of the 'slam-damper', a safety
device between the drier and the baghouse. Whenever a false temperature reading
exceeded maximum it unlatched the air solenoid allowing the damper to shut. This
closed off air flow through the drier, forcing the plant operator to shut down
the plant in order to reset the damper. This was a time consuming operation
since the plant's main fan had to come to a complete halt before the slam-damper
would open. After numerous such restarts the understandably irritated operator
chained the damper in the open position. It was an effective cure for the
moment, but when the generator was repaired a few days later the damper was
overlooked and left disabled. About the same time the propane solenoid valve for
the burner igniter developed a leak. It leaked bad enough to empty three gallon
propane bottles in a matter of hours. Since the operator didn't have a new
solenoid he decided to hook up a twenty five gallon propane bottle and simply
turn it off at night until the new part arrived. This worked fine until the day
of the accident. On that morning when the operator pushed the burner start
button the drier erupted in a ball of flame. The resultant fire ignited the bags
in the baghouse which was eventually gutted. Someone had forgotten to shut off
the propane the night before. As they leaked into the drier, the heavier than
air gasses pooled in the low areas of the unit. With the main exhaust damper
closed there was not enough air to properly purge the drier, though there was
enough to pull some into the baghouse. As a result the burner was ignited with
an explosive mixture in the drier and baghouse. The drier was undamaged except
for some singed paint. The baghouse wasn't so lucky. The slam-damper is a safety
device which normally closes when excessively high temperatures are detected in
the baghouse. This limits the oxygen supply and quickly suffocates any fire
inside the unit. With this safety locked in the open position there was nothing
to prevent the baghouse from being destroyed.
Burner Safety Devices
We take burner safety systems for granted since such things as 'purge timers',
'flame-eyes' and 'over-temperature' devices are built into contemporary burner
controls. These systems are very reliable, normally. But what happens, in the
heat of battle, when one of our safeties fails and our burner won't light? Most
of us will by-pass that particular safety until we can fix it. Sometimes several
related systems can fail and by-passing them can have tragic results.
In both case #2 and #3 the disabling of safety systems was the root cause of the
accident. The incident detailed in case #2 can be traced directly to the
operator's failure to repair the burner 'flame-eye' safety device, and to the
practice of allowing the victim to ignite the burner with a hand held torch.
Repairs to any safety devices should take priority over daily operations,
especially on burner systems. The amount of mix that this particular plant
managed to make while running 'crippled' could in no way compensate for the loss
of that man's life.
It is strongly recommended that you don't disable any safety device but, under
the pressures of production, out in the real world it happens. If you must do
so, the utmost effort must be made to repair that safety device as soon as
possible, preferably in the same day. Extreme caution must be used when
operating any equipment on which the safety devices have been disabled. The best
advice would be to recommend that a company carry spare parts to facilitate
immediate repair of any safety system component. Any other scenario and you are
asking for trouble. No amount of production is worth putting a man's life in
danger.
CASE #4:
Another propane related accident this past
summer illustrates the need for immediate maintenance in potentially dangerous
circumstances. Sadly, this accident was fatal. Workers at a portable drum plant
in the northwest were trying to get the asphalt oil to circulate. The heat
transfer oil system had failed, so they were using a propane torch to heat the
suction and discharge lines to the circulating pump. The shaft packing on the
pump had leaked for several months, so a large accumulation of oil had built up
on the frame around it and on the ground under it. Additionally, the liner had
worn through in the drier discharge collar and a large pool of diesel soaked
asphalt and aggregate had amassed a few feet away from the pump mess. When the
torch ignited the asphalt under the circulating pump the fire quickly spread to
the asphalt under the drier. In minutes a major conflagration engulfed the area.
The loader operator was instructed to take his machine up near the flames and
retrieve the company's portable welder which was in danger of burning. He moved
forward, but the growing flames quickly forced him to a halt. A fifty year old
trucker, attempting to help with the welder, ran behind the loader which
suddenly backed over him. Fatally.
CASE #5:
In the spring of '93 a veteran asphalt plant operator arrived at his plant one
morning to find that his heat transfer oil system had failed to start on time so
his equipment wasn't ready to run. He wasn't surprised, he'd been having trouble
with the start timer, but hadn't yet repaired it.
The operator started the heating system manually, then began adding heat with a
propane torch. He had been heating a jacketed suction line for about ten minutes
when one of the small braided steel lines that carries heat transfer oil to the
suction line failed, spraying him with 300 degree oil. Apparently, as he applied
heat to the heavy 3 inch steel line, he had repeatedly gotten too close to the
smaller line and exceeded it's temperature limit, causing it to rupture. He
spent several months in a hospital, then a year in rehabilitation. Though he
still works for the same paving company, to this day he will not go near the
asphalt plant.
CASE #6:
A northwest asphalt plant was partially destroyed when it caught fire on a windy
spring day. The Madsen, 6000# batch plant was oriented with the drier running
north to south with the hot-stone elevator on the east side. The plant, under
the pressure of production quotas, had been operating sixteen hours a day for
almost two weeks when the accident occurred. Sometime in the previous week the
burner fuel pump, located within ten feet of the burner, had developed a leak
and had spilled enough fuel to soak the ground under the burner.
At higher production rates the seals on the hot-stone elevator leaked prodigious
amounts of fines. On the day of the accident a 40 mile-per-hour east wind drove
these fines into the burner air stream where the extreme heat vitrified it.
Finally, a glowing red-hot clinker fell onto the diesel soaked ground, igniting
it. The flames rapidly burned through the fuel lines feeding the burner fuel
pump. The spreading flames quickly consumed the wiring that fed everything from
the drier back. Luckily, the operator had the presence of mind to run out and
close the valve on his burner fuel tank. Though no one was hurt, the plant was
out of action for almost a week.
Maintenance
The accidents in last three cases can be traced directly to a lack of proper
maintenance. With case #4, If the circulation pump and the discharge collar at
this plant been repaired in a timely manner and the resultant mess cleaned up,
this accident may have never happened. And a good man would still be around
telling jokes and helping those in need. In both #4 & #5 the whole scenario
might have been avoided altogether, had the heat transfer oil systems been
properly maintained and had operated as the manufacturers intended.
In case #6 two events combined to create a hazardous condition: the leaking fuel
line and the leaking hot-stone elevator shaft seal. By themselves, neither
problem was life-threatening. Together they were a blueprint for disaster. As in
cases #4 & #5, a few minutes of repair work would have prevented the whole
scenario.
Two things can work together at your asphalt plant to increase safety: Common
sense and a ridged safety program that includes mandatory meetings to discuss
safety protocols. Effort should be made to discuss other issues in addition to
the basic things like the need for hard hats, eye protection and proper
clothing. In case #1 the operator was wearing a hard hat, but it was of little
use to him in the final analysis.
What all these accidents have in common is a basic disregard for safety. Under
the pressure of production quotas people did things they might not have done
under other circumstances.
For additional information on this subject
or help with any problems encountered
contact Cliff Mansfield,
541-352-7942,
7:30am to 9:00pm Pacific Standard Time.
Email me-
cmconsulting@hotmail.com
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