Gas Detection Solutions for Wood Pellet and Chips Storage

Wood pellet and wood chip boilers are increasingly being considered for use in large-scale power generation as a renewable energy alternative to oil or gas fired boilers.

Wood pellets and wood chip biofuel can produce dangerous, toxic atmospheres in unventilated, enclosed spaces producing Carbon Monoxide and Carbon Dioxide, and depleting Oxygen concentrations.

Wood Pellet and Chips Storage Gas Hazards
Workplace Exposure Limits
Gas Monitoring Solutions

Under suitable conditions of temperature and moisture, wood fuel can provide the nutrients for micro-organisms to grow.  The heat from microbiological proliferation may raise the temperature sufficiently to start the thermal oxidation, generating further heat and eventually leading to increased off-gassing and combustion.

Wood pellets stored in industrial warehouses and domestic storerooms may experience high levels of Carbon Monoxide and Hexanal. The storage of wood pellets in a ship’s hold may encounter Oxygen depletion and produce Carbon Monoxide, Carbon Dioxide, Methane and a range of Volatile Organic Compounds (VOCs).

Fresh wood chips can produce Carbon Monoxide, but not in the same quantities as wood pellets; however, there is still a hazard from Carbon Dioxide emissions and depleted Oxygen.

There are a number of health and safety hazards associated with the transportation and storage of wood pellets and wood chip fuels, including airborne dust, gaseous toxic emissions, spontaneous combustion and asphyxiating and explosive atmospheres. As they are enclosed and there is a reasonably foreseeable risk of serious injury or death, these storage areas should be considered to be confined spaces, as defined by the Confined Space Regulations 1997 (HSE 1997).

Carbon Monoxide and Carbon Dioxide are both asphyxiants. In the UK, Carbon Monoxide has workplace exposure limits (WELs) of 30 ppm (8 hour time-weighted average (TWA)  and 200 ppm (15-minute short-term exposure limit (STEL)). Carbon Dioxide has corresponding WELs of 5000 and 15,000 ppm.

The Approved Code of Practice (ACOP) to the Confined Space Regulations 1997, states that there are substantial risks if the concentration of Oxygen in the atmosphere varies significantly from normal (i.e. 20.9%); and very low Oxygen concentrations (i.e. below 16%) can lead to unconsciousness and death (HSE 1997).

Methane and Carbon Monoxide are both explosive. The lower explosive limit (LEL) for methane is 5% by volume, and 12% by volume for Carbon Monoxide.

Both wood pellet and wood chip biofuel can produce dangerous atmospheres when stored in an unventilated enclosed space. Both fuels can produce Carbon Monoxide and Carbon Dioxide. Wood pellets in particular produce Carbon Monoxide, and wood chip Carbon Dioxide. Both fuels can deplete air of Oxygen.

Before entering the wood storage areas, air quality checks and measurements are to be made using a portable gas detector and gas sampling probe. When entering the store, a personal gas alarm should be worn. Some portable gas detectors can perform both jobs using an internal sampling pump with an attached sampling probe.

When the wood store is opened e.g. for ventilation, access should still be controlled. Air quality checks should include Oxygen measurement as well as Carbon Monoxide and Carbon Dioxide.

For gas monitoring, consider the PS500 which can detect up to five gases with its toxic and catalytic sensors, PID (VOCs) and IR capabilities (Carbon Dioxide)

When pellets are stored in a storeroom, a Scott Safety AVIVA half mask respirator fitted with P3 filters can be worn when entering the store (if worn properly and face fitted, this provides protection against wood dust, but would provide no protection against Carbon Monoxide or an Oxygen deficient atmosphere).

Do you work in the wood storage sector and need some advice about gas detection? Contact a1-cbiss to arrange a site survey or talk to our technical specialists for help with your gas detection needs

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