Risk of carbon monoxide release during the storage of wood pellets

A number of reported fatal accidents have occurred in Europe in the past few years where persons have entered a bulk wood pellet storage hopper or tank and were overcome by carbon monoxide (CO) gas. CO is a colourless, odourless and tasteless gas that is highly toxic.

Wood pellet boilers are commonly used in homes and businesses as an alternative to the oil or gas fired boilers. Wood pellets, the fuel source for these units, are normally housed in a large sealed hopper or tank that is either fitted with screw feeder (auger) connected to the boiler, or the hopper or tank is mounted over the boiler for gravity feeding. Due to the enclosed nature of these hoppers and tanks the atmosphere inside can become oxygen depleted and a toxic atmosphere can accumulate. The Health & Safety Executive (HSE) is advising all operators, maintenance personnel and users of this equipment to do the following:

    1. DO NOT ENTER or place your head into the wood pellet hopper under any circumstances. The unit can contain toxic gases.
    2. Ensure that your wood pellet hopper/tank and boiler has been installed and commissioned by a competent person. If in doubt, contact the supplier and/or manufacturer and request assistance.
    3. Ensure that the boiler is cleaned and serviced by a competent person at the frequency required by the manufacturers’ instructions.
    4. If any problems are encountered with the unit, such as system not heating correctly  or flue gas is flowing into the boiler room, turn unit off and seek assistance immediately.
    5. The responsible person who stores wood pellets, particularly in bulk, should have a suitable risk assessment and safe system of work in place.
    6. Manufacturers, suppliers and distributors of wood pellets should provide adequate health and safety information to the user in their materials safety data sheet.
    7. Warning signs should be placed on the pellet storage area access door, ideally on both sides, so it can be seen when the door is open. The warning sign should include the following information:
DANGER – RISK OF CARBON MONOXIDE POISONING – There is a danger to life from odourless carbon monoxide and lack of oxygen. Check atmosphere before entry with an appropriate device. No entry for unauthorised persons. Keep children away from the storeroom.
– No smoking, fires or naked flames.
– The room should be adequately ventilated before entering. Keep the door open whilst inside.
– There is a danger of injury from movable parts.
– Filling procedures should be carried out accordance to the instructions of the heating installation company and the pellet suppliers.
  1. No personnel should enter the hopper/tank unless fully trained and competent in confined space entry procedures. The hopper/tank should be fully ventilated and controls put in place to ensure safe entry as per the Approved Code of Practice: Safe Work in Confined Spaces (L 101).
  2. Ensure the boiler room is well ventilated at all times to stop inadvertent build-up of toxic gases.