An explosion and a fire while unloading waste from a vacuum truck would change a worker's
life forever.
This is what happened.
A vacuum truck was transporting liquid waste from a natural gas production plant to a hazardous
waste facility for disposal.
Containing hydrocarbons and other substances, the waste was both toxic and flammable.
A generator of hazardous waste is required to inform the receiver of the waste's chemical
composition.
This is done by providing the receiver with an MSDS for the controlled products in the
waste, or a hazardous waste profile sheet that accurately
describes the hazardous ingredients and safe work procedures.
Neither document was provided to the driver or the waste facility.
However, a worker at the production plant did provide
the driver with a hazardous waste manifest stating that the waste was
Petroleum crude oil NOS.
The manifest is used to track the movement of hazardous wastes and is not a substitute
for an MSDS or hazardous waste profile sheet.
The driver filled out a portion of the manifest and a truck ticket used for billing by the
waste facility.
Along with a swamper he then drove there.
At the waste facility, the driver,
the swamper, and a waste operator from the facility
proceeded to unload the waste from the pup tank.
With no MSDS or hazardous waste profile sheet, none of the workers had clear knowledge of
the flammability hazard of the waste.
Two offloading options existed at the waste facility:
a closed hopper system, where the discharge hose is connected to a riser
to offload the waste.
and an open hopper system,
where the waste flows from the truck tank's discharge valve directly into an open hopper.
Solid waste would sometimes block the discharge hose when using the closed system.
The open hopper was routinely used instead of the closed hopper,
partly because doing so eliminated the blockage problem.
The truck was backed in front of the open hopper.
The engine was left running to allow the pup tank to be raised.
The driver opened the isolation valve for the pup tank,
and after receiving the okay from the waste operator,
the swamper opened the discharge valve.
Flammable liquid rapidly flowed from the pup tank.
The waste operator's gas detector's LEL alarm went off.
Vapours moved towards the front of the truck.
The facility's LEL alarm sounded.
The driver yelled, "Get out of here. Go!"
The other workers ran.
Flammable gases and vapours drawn into the truck engine's air intake caused the engine
to speed up.
The driver turned the ignition key to the off position,
but the engine didn't shut down.
Still in the cab, he then activated the engine's positive air
shut-off valve, in order to stop the flow of air and flammable
gases and vapours to the engine.
An explosion followed with a fireball coming out of the cab.
The driver was seriously burned.
How do we prevent similar incidents?
Know the flammability and other hazards of any waste being transferred.
The generator of the hazardous waste must ensure there is an MSDS or hazardous waste
profile sheet for it.
If the waste is transported, a hazardous waste manifest must be completed.
Receivers of the waste should review the documentation.
Ensure risk assessments identify fire or explosion hazards associated with the release of flammable
gas or vapour during the offloading of hazardous waste.
Minimize workers' exposure to hazardous substances.
In the hierarchy of exposure controls, engineering controls should be used before
administrative controls or personal protective equipment.
Engineering controls such as pump-equipped closed hoppers do exist,
but they weren't used at this facility to minimize exposure to gases and vapours from
waste.
Ensure that waste offloading procedures don't allow the airborne flammable gas or vapour
concentration to exceed 20% of the lower explosive limit.
20% is the maximum concentration allowed if it's not practicable to maintain the airborne
concentration of a flammable gas or vapour below the applicable exposure limit such as
in a temporary situation, as during offloading,
or in an emergency.
The open hopper wasn't designed to keep the levels from exceeding 20%.
Control ignition sources.
The investigation found that the truck's engine was most likely the ignition source.
The engine was still running to enable the raising of the pup tank when the waste operator
gave the ok to open the discharge valve.
Learn from what happened here.
If you deal with hazardous wastes, know the dangers and how to control them.