Biomass pellets (principally wood pellets) are a growing dry bulk cargo, with global seaborne trade of approximately 25 to 30 million tonnes per year. The cargo is principally produced in the southeast United States, western Canada, Russia, and the Baltic states from forest and forestry waste, and shipped to large coal-replacement biomass-fuelled power plants in the United Kingdom, the Netherlands, Belgium, Denmark, Japan, and South Korea. The IMSBC Code regulates biomass pellets under a Group B schedule reflecting two principal hazards: off-gassing of carbon monoxide that creates an asphyxiation risk in cargo holds, and self-heating that can lead to fire.
Schedule structure
The IMSBC Code includes the following biomass pellet schedule entries:
- Wood pellets containing additives and/or binders: pellets compressed with binding agents (paraffin, vegetable oils). Group B with potentially elevated combustion characteristics.
- Wood pellets not containing any additives and/or binders: standard industrial wood pellets compressed by mechanical pressure alone, with lignin acting as natural binder. Group B with off-gassing and self-heating hazards.
Both entries are Group B and require compliance with the IMSBC carbon monoxide monitoring, hydrogen monitoring, and ventilation provisions.
Cargo properties
Wood pellets are cylindrical pellets of approximately 6 to 8 millimetres diameter and 10 to 30 millimetres length, compressed from milled and dried wood feedstock. Bulk density is approximately 0.6 to 0.7 tonnes per cubic metre, with stowage factor of approximately 1.4 to 1.6 cubic metres per tonne. Calorific value is approximately 17 to 18 megajoules per kilogram, somewhat lower than coal but sufficient to allow the same power plant infrastructure with adapted handling and combustion.
Off-gassing hazard
Freshly produced wood pellets release carbon monoxide, carbon dioxide, methane, and other gases through chemical and microbial decomposition of the residual wood components. The principal hazard is carbon monoxide accumulation in sealed cargo holds and adjacent enclosed spaces. CO concentrations in confined cargo holds can reach hundreds or thousands of parts per million within days of loading, presenting a severe asphyxiation and toxicity hazard for any crew entering the holds without appropriate gas testing and breathing apparatus.
The IMSBC Code requires:
- Continuous CO monitoring in cargo hold atmospheres throughout the voyage.
- Pre-entry atmosphere testing for any access to the cargo hold.
- Enclosed-space safety procedures including breathing apparatus and gas detection.
- Awareness training for crew that distinguishes biomass pellet cargoes from conventional bulk cargoes that do not present similar risks.
Multiple fatalities have occurred in the wood pellet sector globally, generally involving crew or shore workers entering cargo holds, silos, or enclosed conveyor spaces without proper testing. The hazard is well-recognised, and modern wood pellet handling procedures emphasise enclosed-space safety as a critical training topic.
Self-heating hazard
Wood pellets can self-heat through several mechanisms:
- Microbial decomposition: residual moisture supports microbial activity, particularly in the first weeks after production.
- Chemical oxidation: low-temperature oxidation of cellulose and lignin components.
- Compaction effects: heat retention in the centre of large pellet stockpiles or hold loads.
Self-heating in cargo holds can lead to smoldering fires and, in poorly controlled cases, propagation through the entire cargo. Temperature monitoring during voyage and limiting cargo storage time before shipment (typically below 30 days for new pellets) are the principal control measures.
Dust ignition hazard
Wood pellet handling generates significant dust through breakage during loading, conveyor transfer, and discharge. Wood dust has a defined minimum ignition energy and can produce explosive atmospheres in enclosed handling spaces. Modern wood pellet terminals use enclosed conveyor systems with dust collection and ignition source elimination.
Major routes
Biomass pellet seaborne trade flows include:
- Southeast United States to United Kingdom: the largest trade flow, with Drax Power Station’s Yorkshire site receiving the bulk of US wood pellet exports. Major US export terminals include Wilmington, Mobile, Savannah, and Pascagoula.
- British Columbia to Japan and South Korea: significant Pacific Coast export, with West Fraser, Pinnacle, and Pacific BioEnergy among the major producers.
- Russia and Baltic states to Northern Europe: subject to sanctions complications since 2022.
- Eastern European production to Western European markets: short-sea trade.
Receiving ports are typically dedicated biomass-fired power plant berths with enclosed unloading systems and silo storage capacity matched to power plant demand.
Loading and discharge
Loading is by enclosed shore conveyor and shiploader with dust suppression. Holds must be clean, dry, and have intact ventilation systems. The cargo self-trims and no mechanical trimming is required.
Discharge is typically by enclosed continuous unloader systems delivering pellets directly into shore silos. Some receiving ports use grab discharge but enclosed systems are preferred for dust and CO control.