Research has shown that stored wood pellets are a source of the toxic gas carbon monoxide.

Auto oxidation of wood pellets off gas carbon monoxide (CO). This is a major health and safety hazard for those who store, transport or produce wood pellets. 

Risk to Health

Discharge of carbon monoxide into storage areas is a risk to health.  This needs to be considered in risk assessments wherever pellets are stored and transported.

Factors Affecting CO Release:

  • Temperature
  • Oxygen availability
  • Wood type
  • Humidity
  • Age of pellets

The Danger of Wood Pellets

The chemical composition of wood pellets plays a role in the emission of CO. Oxidative degradation of fatty acids and other organic materials naturally present in wood pellets off gas and produce CO. https://doi.org/10.1093/annhyg/men013

CO is an odorless, colorless gas that binds to haemoglobin around 200 times stronger than oxygen and inhibits oxygen availability in the body. At high concentrations, internal suffocation leading to death can quickly occur. 

The danger of wood pellets comes with their storage or transportation. Wood pellets are often bulk stored and transported in an enclosed area. Without effective ventilation these spaces can quickly become consumed with CO, causing injury or death to those who enter. Fourteen fatal accidents regarding CO poisoning from the storage or transportation of wood pellets have been reported since 2002. https://doi.org/10.1093/annhyg/mes047

Composition and Use of Wood Pellets

Wood pellets are made of compressed saw dust, wood chips, planer shavings and bark. They are used primarily as an industrial energy source to generate heat and electricity but are also used for domestic use. Recently, there has been a dramatic rise in the use of wood pellets as they are a low-carbon alternative to coal and other fuels

Case Studies

Two different studies simulated warehouse conditions measuring the emission factors of CO off-gassing from wood pellets.

Both studies found concerning levels of CO at room temperature or above (Figure 1 and Figure 2). 

Figure 1: CO concentrations in the drum with bagged hardwood pellets as a function of temperature at a constant RH of 30%.

From https://doi.org/10.1093/annweh/wxx104  [Supplementary material]

CO concentrations in the drum with bagged hardwood pellets as a function of temperature at a constant RH of 30%.

Figure 2: CO concentrations in the 45-1 containers as a function of storage time at different storage temperatures using wood pellets from British Columbia.

From https://doi.org/10.1093/annhyg/men053

CO concentrations in the 45-1 containers as a function of storage time at different storage temperatures using BC wood pellets.

Tips for Managing Carbon Monoxide from Wood Pellets

  • Store wood pellets in a cool and dry area
  • Active ventilation is key
  • Place visible signage near the hazard
  • Measure CO and oxygen levels prior to entry and during occupation of storage spaces containing wood pellets

Conclusion

Wood pellets off-gas lethal amounts CO. The biggest risk of CO poisoning from wood pellets is in the storage or transport industries. If you think you may be at risk of CO exposure, contact K2 Environmental for advice or professional assessments.