If anyone feels headache, nausea, dizziness, clumsiness or confusion near a running gasifier, get out into fresh air upwind first and deal with the vehicle afterwards, because a 1% leak of the gas flow into a sealed 3 m³ cab reaches about 6,700 ppm of carbon monoxide in 7.5-12 minutes. For a fire, close the air inlets and smother with sand; never use water on a hot gasifier; and for tar clogging, stop and let the unit run hot on the blower before resuming.
Part of Operating Procedures
Emergency procedures for a wood gas vehicle: carbon monoxide exposure, fire, flashback and tar clogging.
Carbon Monoxide: Leave First
The carrier’s order for a gas leak is: stop immediately, turn off the gasifier, open all windows, exit the vehicle and ventilate. That puts the controls and the windows before the exit. The first symptoms are exactly the ones that remove the judgement to leave, so the safe order is the reverse: get out and upwind first, then switch off or ventilate from outside if it can be done without going back into the cab or closed space.
Why the order matters, with illustrative numbers. A small car cab is about 3 m³ (an assumption). The carrier’s vehicle gas flow is about 50-80 m³/h. A leak of 1% of that flow is 0.5-0.8 m³/h of gas, about 20% carbon monoxide.
- 0.1 m³ of gas in 3 m³ is 0.1 × 0.20 ÷ 3 = 0.67% carbon monoxide = 6,700 ppm.
- 0.1 m³ takes 0.1 ÷ 0.5 = 0.2 h = 12 min at 0.5 m³/h and 0.1 ÷ 0.8 = 7.5 min at 0.8 m³/h.
- The level immediately dangerous to life is 1,200 ppm, so 6,700 is 5.6 times that.
A leak you cannot smell or see can be lethal in under a quarter of an hour in a closed cab, and carbon monoxide mixes evenly through the space, so there is no safe height. A moving vehicle with windows open dilutes it, which is why the cab should be vented.
If Someone Is Overcome
- Do not go into a closed space after them. The rescuer breathes the same air; open the space from outside and ventilate, or pull the person out if it can be done in seconds from fresh air.
- Move them upwind into fresh air, lay them on their side if unconscious (Recovery Position), and check breathing. If they are not breathing, start CPR (CPR Technique).
- Keep them warm and still, and get help. Oxygen is the treatment and there is none; fresh air is the substitute.
- Even if they recover, keep them resting and watch for headaches, confusion or memory problems over the following days.
Carbon monoxide binds to haemoglobin about 200 times more strongly than oxygen, so the effect builds over an exposure and clears slowly. See CO Risk.
Gasifier, Hopper Or Filter Fire
Close all air inlets and smother with sand or earth, as the carrier says. Do not use water on a hot gasifier: it flashes to steam, and on hot charcoal it makes more fuel gas (hydrogen and carbon monoxide). Move people and the petrol system away from the fire first.
Flashback Or Explosion
A gasifier is a vessel holding combustible gas and a fire. When air gets into it, especially on restart with a hot bed and a gas-filled chamber, it can flash back or explode. Producer gas in air is flammable above roughly 17% gas by my Le Chatelier estimate in Mixing Valve & Air-Fuel Ratio. Keep out of the line of the hopper lid, never open a hot unit, and after a flash do not reopen it until it is cold.
Tar Clogging
Misfires and loss of power mean the gasifier is running too cold, as the carrier says. Stop outdoors, switch to petrol, run the blower with the flare lit, and resume on gas only when the flare is clean. If the pipes and filter are tarred, shut down and clean them cold.
Common Mistakes
- Trying to switch off before leaving. The time spent is the exposure.
- Going back in for a colleague. That doubles the casualties.
- Water on a hot unit.
- Using a flame to look for a gas leak. Use soapy water on a low-pressure air test.
Safety
Carbon monoxide gives no warning and removes the will to leave
Producer gas is about 18-22% carbon monoxide by volume, odourless and colourless. Headache, nausea, clumsiness and confusion arrive before collapse; people sit down, decide to finish the job, or go back for someone. Never run, light, refuel or purge a gasifier indoors, in a shed or lean-to, or in an enclosed yard, and never sleep in or near a vehicle with it lit. A hot bed full of gas and air can flash or explode. See Carbon Monoxide Risks.
What’s Next
- Learn next: Performance & Limitations — what the vehicle can and cannot do
- Combine with: Startup Sequence (20-30 Minutes) — the phase with the highest exposure