Fueling, DEF & Diesel Safety

Fueling is part of every driver’s day, and it’s where many slips, spills, fires and costly mistakes happen. Modern diesel trucks also use diesel exhaust fluid (DEF), a second fluid that must never be confused with fuel. Knowing the safe steps for both protects you, your truck and your paycheck.

• Truck Drivers
• Fleet
• Delivery

Diesel fuel hazards

• Fire: diesel is harder to ignite than gasoline, but it burns, and vapors and mist can ignite from a spark, a hot exhaust or a lit cigarette. Spilled fuel on a hot engine is a fire risk. See Flammable Liquids.
• Slips and falls: spilled diesel is slick, and so are wet steps, tanks, ice and snow. Falls from steps, tanks and fuel island ramps are common. See Climbing In & Out and Slips, Trips & Falls.
• Skin and eye contact: diesel dries and irritates skin and can cause dermatitis. Prolonged contact, such as fuel-soaked clothes, can cause more serious problems. Wash it off.
• Breathing vapors and exhaust: diesel exhaust contains particles and gases that irritate the lungs, and the International Agency for Research on Cancer classifies it as carcinogenic to humans. Don’t idle in enclosed areas. See Diesel Exhaust.
• Environmental harm: fuel spills pollute water and soil and bring fines.

Fueling safely: step by step

1. Park in the fueling lane, set the parking brake, chock if needed and shut off the engine and any auxiliary equipment. Turn off heaters and refrigeration units that could ignite fumes.
2. No smoking or open flames, and no phones in the way of distraction. Don’t use a cell phone while fueling if the site prohibits it.
3. Use three points of contact on the steps and hold the grab handles when you climb to the tank. Don’t jump down.
4. Choose the right pump and nozzle. Diesel nozzles are usually green at truck islands. Check the pump label to make sure it’s diesel, not gasoline.
5. Stay with the nozzle and hold it while fueling. Don’t jam the latch open with a tool or object, and don’t leave it unattended. If the site has a hold-open latch, you must still stay at the nozzle.
6. Don’t overfill. Stop at the automatic shutoff, and leave room for the fuel to expand. Overfilling causes spills and is unsafe.
7. Replace caps securely, and close and latch the nozzle.
8. Clean up small spills right away or report them to the station. Never drive away from a spill. Use absorbent for larger spills, and call the station. See Spill Response.
9. Check the area and pull away only when everything is closed and clear.

• Don’t fill portable containers in the truck bed. Set them on the ground. See Static, Bonding & Grounding.
• Don’t siphon fuel by mouth, or use fuel to wash your hands or tools.
• Don’t top off tanks while the truck is hot, or if it’s parked on a slope.
• Don’t rush. Most fueling injuries happen when drivers are in a hurry or tired. See Driver Fatigue.

What DEF is

• Diesel exhaust fluid (DEF) is a clear, colorless liquid that is about 32.5 percent urea in 67.5 percent deionized water. It is sold as DEF or by brand names such as AdBlue.
• Modern diesel engines use selective catalytic reduction (SCR) to cut nitrogen oxide emissions. DEF is sprayed into the exhaust, where it turns pollutants into harmless nitrogen and water.
• DEF is not a fuel and not an additive. It goes in its own tank, usually with a blue cap, near the diesel tank. If the DEF runs out, the engine may reduce power or limit speed, and may not restart, depending on the truck and the emission rules.

Never mix DEF and fuel

• The DEF filler has a smaller neck than the diesel filler, and fuel nozzles don’t fit, but dispensers and jugs can be confused. Check the label and the cap color before you pour.
• Use only DEF that meets the standard (ISO 22241 / API certified), from a clean, sealed container or a DEF pump. Don’t use water, window cleaner or other liquids in the DEF tank.
• Keep the DEF tank free of dirt and don’t put funnels used for other fluids into it.

Handling and storing DEF

• DEF is not flammable or explosive and is generally low in hazard, but it can irritate skin and eyes, and corrodes some metals, such as copper, brass and carbon steel. Wear gloves and eye protection when you handle it, and rinse spills with water.
• Wipe up spills. Dried DEF leaves white crystals that can clog parts and slip hazards. Rinse the area with water.
• Storage temperature matters. DEF freezes at about 12°F (−11°C). Frozen DEF is fine to thaw, and the truck has a heater, but it expands, so don’t overfill a container. Keep DEF out of long exposure to heat above about 86°F, and out of direct sun. It has a shelf life of around a year or less, depending on storage.
• Keep containers closed and clean, and store them upright. Use containers made of compatible plastic or stainless steel.
• Follow the Safety Data Sheet. See Safety Data Sheets.

Cold weather and other conditions

• Diesel can gel in cold weather. Use winter-blend fuel and anti-gel additives as directed, and keep tanks full to reduce condensation. See Winter Trucking.
• Ice around fuel islands and steps is a big fall risk. Watch your footing, and use gloves.
• Hot weather makes fuel expand and vapors rise. Don’t fill to the very top.
• Fuel theft is a problem at night. Use locking caps and park in well-lit, secure areas. See Truck Parking.

If something goes wrong

• Fuel fire: hit the emergency fuel shutoff at the pump, move away, call 911 and use an extinguisher on a small fire only if you can do so safely. See Fire Extinguishers (PASS).
• Diesel on skin or clothes: remove soaked clothing and wash skin with soap and water. For eye contact, flush with water for at least 15 minutes. See Chemical Exposure First Aid.
• Wrong fluid in a tank: don’t start the engine. Call your dispatcher or roadside service.

Fueling checklist

• Engine and auxiliary equipment off; parking brake set; no smoking
• Right pump and nozzle for diesel; I stay with the nozzle
• Three points of contact on steps; careful footing on wet or icy ground
• No overfilling; caps closed; spills cleaned up or reported
• DEF goes only in the blue-cap DEF tank; never mixed with fuel
• Gloves and eye protection for DEF; skin washed after contact

Last updated: October 4, 2026