OSHA Hazard Information Bulletins
December 6, 1995
| MEMORANDUM FOR: |
REGIONAL ADMINISTRATORS |
| FROM: |
STEPHEN MALLINGER
Acting Director
Directorate of Technical Support |
| SUBJECT: |
Hazard Information Bulletin(1) - Cleaning of Asphalt
Truck Hopper with Diesel Fuel |
________
FOOTNOTE(1) The Directorate of Technical Support issues Hazard
Information Bulletins (HIBs) in accordance with OSHA Instruction CPL 2.65
to provide relevant information regarding unrecognized or misunderstood
health hazards, inadequacies of materials, devices, techniques, and
engineering safety controls. HIBs are initiated based on information
provided by the field staff, studies, reports and concerns expressed by
safety and health professionals, employers, and the public. Information is
compiled based on a through evaluation of available facts, literature and in
coordination with appropriate parties.
The Ministry of Transportation of Ontario, Canada has brought to our
attention that a truck which is manufactured in the United States for
patching asphalt may cause hazardous conditions during the cleaning process.
Prior to the use of this type of truck, hot asphalt (about 250 degrees F) was
loaded into a dump truck, taken to the worksite, and used for road surface
patching until the material cooled to the point when it could no longer be
used. It was then discarded.
The vehicle, which is made in California, is capable of keeping the asphalt
hot. It has an insulated hopper/conveyor unit, with both an indirect propane
and an electric heater in the insulation layer of the double wall unit. The
unit is top loaded at an asphalt plant and unloaded from a conveyor belt on
the bottom interior of the hopper. The hopper is usually precoated with
diesel fuel at the asphalt plant prior to loading. The hose between the metal
spray wand and the hopper pump is not made of conductive material. Cleaning
of the unit usually takes place while the hopper is not yet fully cooled, so
the residual asphalt is more easily removed.
An explosion occurred during the process of cleaning the hopper. The
operator was standing at the rear of the vehicle, wearing rubber boots,
holding the spray wand inside the rear of the hopper through the conveyor
chute. The top doors of the hopper through which asphalt is loaded were
closed. It is believed that a static electrical charge had accumulated on
the spray wand due to the flow of the diesel. The charge resulted in a spark
jumping from the wand to the metal hopper, as the wand came close to the side
wall, while atomized diesel was being sprayed from the nozzle. The hopper
interior was above the flashpoint (105 degrees F) of diesel fuel. This led to
the ignition and explosion of the diesel vapors contained inside the hopper.
The explosion force was directed out of the rear conveyor chute opening,
since the top doors were closed. The operator was blown backwards, suffered
2nd degree burns to 45% of his body and 3rd degree burns to his hands and
arms.
It should be noted that any source of ignition, not just a static electrical
spark, could also have caused this explosion. However, the presence of such
sources could not be verified.
As a result of this incident, the Ministry of Transportation of Ontario has
recommended that the asphalt trucks be immediately taken out of service until
completion of the investigation and implemented the following
recommendations:
* Standard operating procedures for operation and cleaning of the
asphalt trucks must be established;
* A mechanism for mechanically grounding the truck and hopper to
earth ground prior to cleaning or spraying must be provided;
* The worker must consciously make contact with the truck
immediately prior to spraying, to ensure no charge is on his or her
body;
* The asphalt patcher unit must be sprayed when the unit is cold
and only for precoating;
* The spray wand and supply hose must be bonded and
grounded;
* Asphalt residues must be removed with a long handled mechanical
tool to minimize the diesel fuel needed for cleaning once the hopper is
cool;
* The interior of the hopper must be allowed to cool to below 86
degrees F (30 degrees C) prior to spraying diesel;
* A non-atomizing nozzle to spray the interior of the hopper and
tools must be used;
* The top loading doors must be opened during diesel spraying,
and the operator must spray the diesel into the top (larger) hopper
opening;
* A hopper internal temperature gauge must be installed for operator information;
* Explosion proof switch must be installed to replace current
diesel pump/propane burner power switch at rear of the unit, and wired so
that only one unit can function at any time; and
* "No Smoking Within 10 feet" signs must be posted on all four sides of the tank.
Workers involved in the cleaning of the hopper also must use appropriate
personal protective equipment and receive training on this procedure.
The Ministry of Transportation of Ontario also recommended that a safer
substitute material for the diesel fuel, such as a water soluble product to
be sprayed on the interior surface of the hopper to minimize the quantity of
material that clings to the walls, be reviewed and considered.
Compliance and consultation personnel should be aware that such asphalt
trucks are in use and that improper cleaning procedure can result in
explosion and has caused injuries to workers. Additionally, they should be
aware of the recommended cleaning procedures to control this hazard.
Please distribute this bulletin to all Area Offices, State Plan States,
Consultation Projects and appropriate local labor and industry associations.
Copies of this HIB may be used for outreach purposes.
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