The Use of Biomass – General Paper

A Summary Paper – COSHH Hazards arising with the storage of wood fuel

Author: A J Nicol BSc CEng MEI

Introduction

It is appropriate to note that the comminution of aged timber will produce dust of all sizes including tiny particulate regardless of fuel specification. That dust will contain or have attached any of the residues of any chemical treatments etc and will because of its size remain airborne for long periods, post shredding and movement. Inhalation will present a COSHH risk (particularly with organo-chlorides) and will, very likely, with accumulation present an explosion risk. The risk of explosion will be most acute with enclosure e.g. above conveyors that are enclosed (reference the OSB investigation into the Imperial sugar explosion). Where wood is treated or where wood is wet and rotting wood is stored there is also the inherent risk of fungal growth and the attendant COSHH risk.

The use of Biomass has increased significantly over the last ten years. This increase is in large part due to a perception that biomass is green, clean and sustainable. These conceptions are in part driven by market pressure and in part underwritten with Government commercial interventions. The rapid development and deployment of biomass has alarmingly resulted in the un-informed design, review, installation and operation of allied storage and combustion technologies (with attendant fatality and injury)

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Summary

The research and information and in particular the  formulation and execution of large scale trials for CO production from wood chip is very limited. There is sufficient evidence to show that large scale storage of any organic material but in particular soft wood lumber or chip will produce CO and generate and oxygen depleted high CO₂ atmosphere. Where headspace ratio is small that will result in unacceptable CO levels.

Entry to a space storing large quantities of organic materials requires special and sensible consideration and precaution.

My consideration is based on this very limited data and analysis available for fresh wood chip. In the context of auto oxidative CO formation at least this will provide some safety margin because there is research available which suggests that the fatty content of wood reduces with age and accordingly the propensity to generate CO reduces.

Keeping the wood very dry will hamper biological degradations with attendant, CO, Methane and CO₂ production, and for that reason ahigh fuel turnover and no dead spaces are preferable.

Ventilation must assure mixing or else stratification or binding may occur, creating pockets or layers of high CO concentration.

The detection systems must at least detect at the level where any human operator might be. Additional low and high level alarms might be used to provided a robust alarm system and warning of over pile CO build up and stratification.

Operational and maintenance activity that requires entry to a large store will merit special precaution. e.g. a risk assessed entry, COSHH test, extraction and evacuation procedures (written and tested) – and published emergency procedures to mitigate the effects of any Hazard being realised e.g. initial healthcare procedures for persons suspected of carbon monoxide poisoning or Oxygen deficiency.