Diesel Exhaust and the Idling Truck

Why this matters

The service truck is the one piece of equipment every crew member is around every day, and on a lot of jobs it idles: to keep the cab warm while the crew eats, to run a power inverter, to keep the heater going between stops. Diesel exhaust is classified as a human carcinogen, the people breathing most of it are the crew in and around their own truck, and the house the truck is parked against has air intakes and open doors that pull exhaust inside. None of it is visible on a modern engine, which is exactly why it goes unmanaged.

What diesel exhaust is

Diesel exhaust is a mix of gases and particles.

• Diesel particulate matter (DPM) is soot: a carbon core, mostly far smaller than a micron, coated with organic compounds that include known carcinogens. Particles this small reach the deep lung.
• Gases include nitrogen oxides (nitric oxide and nitrogen dioxide), carbon monoxide at lower levels than a gasoline engine produces, sulfur dioxide (much reduced since ultra-low-sulfur fuel), aldehydes such as formaldehyde, and hydrocarbons.

The cancer classification. In 2012 the International Agency for Research on Cancer moved diesel engine exhaust to Group 1, carcinogenic to humans, on sufficient evidence for lung cancer, drawing heavily on studies of miners and other workers with long, high exposure. NIOSH has treated diesel exhaust as a potential occupational carcinogen since 1988. Short-term effects at high levels include eye and throat irritation, headache, lightheadedness and worsened asthma.

Newer engines are much cleaner, not clean. US on-road diesel engines built to the 2007 and 2010 emission standards use particulate filters and nitrogen oxide aftertreatment that cut particulate emissions by roughly 90 percent or more compared with older engines. The IARC classification was built on exposure to older technology. A late-model truck in good repair emits far less soot, but it still emits nitrogen oxides and other gases, and an older truck, a truck with a removed or failed particulate filter, a generator or a piece of construction equipment can still put out heavy soot. Treat "it's a new truck" as a reason the dose is lower, not a reason it is zero.

The enforceable limits are thin

There is no general OSHA standard for diesel particulate. The only US numeric DPM limits are MSHA's, and they bind mines, not service trades. For a field service shop, OSHA's limits reach diesel exhaust only through its individual gases, in Table Z-1 of 29 CFR 1910.1000 for general industry and 29 CFR 1926.55 for construction: carbon monoxide at 50 ppm as an 8-hour average, nitrogen dioxide as a ceiling of 5 ppm. NIOSH's recommendation for carbon monoxide is stricter, 35 ppm. So the shop's real obligation is the ordinary duty to keep workplace exposure low, and the practical controls are cheap. See related: Dose, Route and the Exposure You Cannot See.

Where the dose actually lands

The crew in the cab. Studies of truck and bus cabs have found that idling, especially with windows cracked, doors opening and closing, or the ventilation pulling from outside while parked, can draw the truck's own exhaust into the cab. Leaks in the exhaust system or the cab seals make it worse. A crew that sits in an idling truck for a 30-minute lunch every day accumulates a real share of its exposure in the one place everyone thinks of as a break.

The crew at the tailgate. On a utility body, the tailgate and side compartments are where the crew works. A tailpipe or exhaust stack at that corner puts fresh exhaust at breathing height for whoever is cutting, fitting or loading.

The customer's house. A house is a set of openings that draw air: a heat recovery or energy recovery ventilator (HRV or ERV) fresh-air intake on an exterior wall, a furnace or water heater combustion-air intake, a bath or kitchen exhaust that pulls make-up air from leaks, an open garage door, an open front door during the job, a window unit. A truck idling in the driveway with its exhaust pointed at any of them puts diesel exhaust in the house, where the people exposed are the customer, the children and anyone with asthma.

Anti-idling laws: the state layer

There is no general federal idling limit for commercial trucks. The rules come from states, counties and cities, and they vary widely in who they reach and how long they allow.

• California limits idling of diesel-fueled commercial vehicles over 10,000 pounds gross vehicle weight rating to 5 minutes at any location, under a state air board rule, with listed exceptions.
• Massachusetts limits unnecessary idling of motor vehicles generally to 5 minutes, also with exceptions.
• New York City sets 3 minutes, and 1 minute next to a school.

Many other states, counties and cities have their own limits, often 3 to 5 minutes, sometimes applying only to heavy vehicles, and many states have none. Exceptions commonly cover traffic, vehicle servicing, and power take-off use, and whether running an inverter or a compressor for work counts as an exempt use varies by jurisdiction. Check the rule where your trucks operate rather than assuming one applies everywhere.

The point for a shop is that the health control and the legal limit point the same way: the engine should be off unless it is doing work.

Placement: what the truck's position does

         HOUSE (side wall)
   +-----------------------------------+
   |  [ERV intake]        [open garage] |
   +-------^----------------------^-----+
           |                      |
      exhaust drawn in       exhaust drifts in
           |                      |
   ~~~ wind toward house ~~~~~~~~~~~~~~~~
   [tailpipe]<====TRUCK (idling)=====>
           crew at tailgate ->  X

The diagram is the common bad layout: the truck backed in with its tailpipe near the house, a light wind carrying exhaust toward an intake and an open garage, and the crew working at the tailgate next to the pipe. Turning the truck around, or parking it at the curb, moves the tailpipe away from both the house and the crew without changing the work.

Worked example: a winter water heater swap

A two-person crew arrives at a house at 7:30 in the morning in 20 F weather to replace a water heater in the attached garage. The truck is a diesel with a utility body, model year about 12 years old with its particulate filter intact. The job will take about 3 hours. The house has an ERV with its fresh-air intake on the garage-side wall, about 6 feet above the driveway.

What happens by default. The crew backs the truck up the driveway to within 10 feet of the open garage door so the old tank has a short carry. They leave the truck idling for the cab heat and to run an inverter for a work light and a reciprocating saw. With the tailpipe on the driver's side rear, facing the house, a light wind carries exhaust toward the garage door and the ERV intake. Over 3 hours the truck idles for most of it, and the crew works much of that time at the tailgate.

Applying the controls.

• Engine off by default. The saw runs on a battery tool; the work light runs off a cord from a garage outlet with the customer's permission. That removes the reason to idle for power. Whatever the state limit, a 3-hour idle for a work light is not something a shop should defend.
• Park with the tailpipe away from the house. The crew parks nose-in, or at the street edge of the driveway, so the tailpipe faces the street. The extra carry for the old tank is about 20 feet.
• Close the garage door between carries when it is not needed open, because the garage connects to the house and the ERV.
• Lunch with the engine off, or in the truck for a short warm-up only with windows closed and the cab ventilation set to recirculate, and never with the tailpipe close to a wall or a snowbank that traps exhaust under the truck.

What would change the call. If the job genuinely needs engine-driven power, a PTO-driven compressor or a welder on the truck, the work justifies running the engine, and the controls become placement and wind: tailpipe downwind of the house and the crew, intakes and doors closed on that side, and the customer told why. If the truck were a gasoline engine, the particulate story changes but carbon monoxide rises sharply, and the same placement rules matter more, not less. See related: Carbon Monoxide From Your Own Tools. If the truck's particulate filter were removed or failing (visible black smoke on acceleration), that is a fleet repair issue and, in many states, an emissions violation, not something to manage with parking.

The failure mode. The common one is not dramatic. A customer with a child who has asthma notices the house smelled of exhaust the day the crew was there, or an ERV with its filter darkened by soot, and calls the office. The crew's own exposure is invisible and accumulates for years.

Shop-level rules worth writing down

• Engine off at the job unless it is driving work equipment.
• Park with the exhaust away from the house and its intakes and away from where the crew works.
• No lunch breaks in an idling cab with the exhaust near a wall, a snowbank or another vehicle.
• Report exhaust leaks, visible smoke and cab exhaust smell to whoever maintains the fleet, and fix them.
• Know the idling rule for every jurisdiction the trucks work in.

References

• IARC Monographs Volume 105 (2014), diesel and gasoline engine exhausts, diesel exhaust classified Group 1 in 2012
• NIOSH Current Intelligence Bulletin 50 (1988), carcinogenic effects of exposure to diesel exhaust
• OSHA 29 CFR 1910.1000 Table Z-1 and 29 CFR 1926.55, carbon monoxide and nitrogen dioxide limits
• California Air Resources Board commercial vehicle idling regulation; your own state and local idling rules
• See related: Carbon Monoxide From Your Own Tools; Dose, Route and the Exposure You Cannot See