On 29 April 2015 World Maritime News reported the tragic death of a seaman on board a Polish container ship. The vessel Corina, carrying a cargo of wood pellets, was being unloaded at Port Hanstholm in Denmark when four seamen became unconscious. One died and the others were hospitalised. The cause of the accident is thought to be asphyxiation due to oxygen depletion. Sadly this is not an isolated case. Despite the known hazards of working in confined spaces, particularly when they contain oxidising materials or substances, such incidents still occur.
A few months earlier, in January 2015, the International Convention for the Safety of Life at Sea (SOLAS) had amended its guidelines for working in confined spaces. The SOLAS regulation III/19 now stipulates that at least every two months, appropriate crew members must perform an emergency drill on confined space entry and rescue procedures. This was SOLAS’s response to a perceived need for regular safety training for workers on dry bulk carriers. The Corina’s freight, wood pellets, is an increasingly common material whose innocuous appearance belies its intrinsic danger.
Organic products such as timber and wood chips have a tendency to degrade the surrounding air when they are stored in confined spaces. The natural processes of microbiological activity and chemical decomposition can quickly deplete the ambient oxygen, as well as increasing the carbon dioxide and generating carbon monoxide. Any one of these things could render the air unsafe but when two or more exist together they can become a lethal combination. Other bulk dry cargoes that are known to cause oxygen depletion include coal, grain products, natural fibres, iron and steel.
The potentially hazardous storage of biofuels is not restricted to ocean-going transport. The increasing use of wood-fired boilers in non-domestic heating systems requires the construction of large storage and delivery systems. So far there have been no UK fatalities but in mainland Europe there were nine deaths between 2002 and 2012. To highlight these risks, the UK Health and Safety Executive issued a Safety Notice in 2012, ‘Risk of carbon monoxide release during the storage of wood pellets’.
The carbon monoxide (CO) responsible for the European fatalities is believed to have resulted from ‘off-gassing’ of the biofuels (note that CO can also be caused by incomplete burning of fuel, but that topic is not covered here). Another gas which is created, carbon dioxide (CO2), can also be very harmful. Furthermore, the ambient oxygen (O2) in a fuel store may drop as a result of oxidation, and this is also a potentially lethal situation. These risks are compounded by the fact that CO and CO2 have no colour, taste or odour and have been known to cause rapid unconsciousness and death.
The HSE Confined Spaces Regulations 1997 state that, ‘Some spaces may meet the criteria to be a confined space when they are used to store…wooden pellets used as fuel in heating systems …Oxygen deficiency can result from many processes and the storage of many different products including…wood pellets used as biofuel…A lack of oxygen in the atmosphere may also lead to asphyxia or unconsciousness…’ Therefore before entering a confined space workers must be trained in the correct procedures, adequate ventilation should be applied and the O2, CO2 and CO checked.
Author: Paul Smith, Technical Writer