Asphalt Plant Safety - Part I
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 No. 1
It was little past 7 a.m. A long line of trucks waited at the plant when the superintendent drove up to the plant. 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 and two kids. The devastated superintendent took early retirement.
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-tagout” procedures.
The Occupational Safety and Health Administration (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 No. 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 ignitor 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 the injuries.
Case No. 3
Another West Coast plant suffered a catastrophic explosion and fire for similar reasons in 1994. Fortunately, no one was killed. Two unrelated events combined to form a potentially lethal situation. Earlier in the week the plant, a 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, because 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 ignitor developed a leak. The leak was bad enough to empty three gallon propane bottles in a matter of hours. Because the operator didn’t have a new solenoid, he decided to hook up a 25-gal 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 gases 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 because 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 the 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 No. 2 and No. 3, the disabling of safety systems was the root cause of the accident. The incident detailed in case No. 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 crew member’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 crew member’s life in danger.
Case No. 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 50-year-old trucker, attempting to help with the welder, ran behind the loader, which suddenly backed over him.
Case No. 5
In the spring of 1993, 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 10 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-in. 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 No. 6
A northwest asphalt plant was partially destroyed when it caught fire on a windy spring day. The 6,000-lb 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 16 hours a day for almost two weeks when the accident occurred. Sometime in the previous week the burner fuel pump, located within 10 ft 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-mph 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.
The accidents in the last three cases can be traced directly to a lack of proper maintenance. With case No. 4, if the circulation pump and the discharge collar at this plant had been repaired in a timely manner and the resultant mess cleaned up, this accident may have never happened. In both No. 4 and No. 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 No. 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 No. 4 and No. 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 rigid 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 No. 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 normal circumstances.