LAWR

HEALTH & SAFETY Health and safety management in anaerobic digestion With a rapidly expanding base of anaerobic digestion (AD) plants across the country, the health and safety and competence of the growing workforce is an issue which project developers, local authorities, the waste industry, farmers and the renewable energy industry need to take very seriously. Kevin Thrower finds out why. aste can be dirty and dangerous sometimes. Workers are often hands deep in differ- ent waste materials so protecting them is vital to ensuring a safe working environment. With 130 operational sites and 340 under devel- opment, the number of AD sites are moving from the design and construc- tuion phase into commissioning and full scale production. This means AD operators are facing new health and safety challenges. During this time of change, when the pressure to create a positive cash flow begins to rise, it is prudent for AD management to consider the potential 'Process Safety' and competence issues that could affect their operations. Process Safety differs from occupational safety in that the latter addresses behavioural issues such as trips, slips and falls, as well as safe systems of work including 'Permit to Work', whilst Process Safety relates to the systems and competence of a plant and its people (from executives to operators) in ensuring that all materials used within an AD process remain inside the plant and equipment. Hazardous scenarios If materials (for example digestate, biogas or biomethane) do escape then there is the potential for a serious injury or contamination of the environment. Scenarios that could occur include a 'Foam Over' from a digestor, that is not contained in the vessel or site bund, and then seriously contaminates a local water course, or a gas leak inside a cabin or site building that is not detected and causes asphyxiation of an unsuspecting employee. If a risk-based system of hazard recognition and mitigation is employed then the probability of these occurring, if a plant is designed and operated correctly is low. However, evidence collected from a fire at a major fuel depot at Buncefield in Hertfordshire in December 2005, indicated that some of the contributing factors included: • Poor understanding and lack of training in Process Safety at all levels in an organisation; • Maintenance activities not being carried out or completed satisfac- torily; • Poor communications between employees, especially at hando- vers; and • The interface with contractors. As AD plants move in to their operational phase, AD operators should consider how to mitigate against ways of working that could jeopardise their operations relating to Process Safety. Evidence collected from a host of major incidents has shown that poorly maintained safety critical systems has contributed significantly to the chance of a Process Safety incident. Site operators should ensure that instruments and control loops that provide protection to the equipment are tested and inspected to an agreed schedule. They should also keep records of these inspections and regularly review if the inspections are being completed. This will help set a measure or a 'Leading Indicator', helping reduce the risk of a Process Safety incident. Examples include regularly testing the 'High Level Alarm' instrument and trip on a digestate storage tank and the W June 2014 Local Authority Waste & Recycling 23 • Do staff employed have the level of competence to understand their obligations in process safety? • Are there maintenance processes in place that identify all the safety critical systems and their testing requirements? • Are management to staff communications issued without ambiguity? • Is the process of accepting plant responsibility from one employee to another completed robustly? Questions AD operators should ask themselves to help mitigate against ways of working that could jeopardise their operations relating to process safety: ►

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