Generally, improving technology provides a safer healthier workforce, if only by automating and reducing the number of personnel exposed to a particular risk, and this is true of compressed air. However real momentum in respect of improving compressed air technology, understanding and safety within tunnelling has only been achieved in comparatively recent years.
In 1958, ’63 and ’66 the UK introduced new codes of practice and decompression schedules which radically changed the approach to compressed air tunnelling and at the time represented a major improvement in working practice which previously had received little upgrade or modification. These formed the basis for new international standards. Although minor amendments were made to these new codes over subsequent years, they remained largely unchanged until the early 1990’s, by which time they were significantly outdated by advances in other hyperbaric industries, notably offshore diving. This left an industry well equipped in engineering terms to deal with the application of compressed air, but relatively ignorant as to improving hyperbaric practice and the potential to significantly advance associated workforce health & safety.
Modern Legislation
In the mid 1990’s, the UK Health & Safety Executive responded to a combination of its own research into high levels of worker injury, growing concerns based on increasing awareness from within the industry and critical analysis from those coming into or advising the industry. The resulting action was the publication of the UK Work in Compressed Air Regulations 1996. This for the first time gave real guidance to compressed air contractors as to standards for medical surveillance, training, safe management of hyperbaric work, competent personnel and plant and equipment.
In September 2001, revisions were made to the decompression procedure (approved under the UK regulations) following continued commitment to research and critical analysis. The revisions now provide for the compulsory use of oxygen assisted decompression techniques and clear indications for equipment standards and safe systems of work. They have extended the clinical and occupational health responsibilities of the Contract Medical Advisor and define clearly the necessary qualification, experience and responsibility of those implementing hyperbaric procedures and operating lock systems.
Modern Working
Focusing around the new legislation, it is now essential to first carefully plan compressed air work to be undertaken to ensure compliance and second that the most appropriate working practice is applied. This involves a full analysis of all the potential risks, hazards and occupational health issues that will arise from the application of compressed air and potential consequences for the overall tunnelling plan, project progress and the ongoing health & safety of those carrying out the work. Contingency for this is normally covered under "Project Specific Operational & Emergency Procedures for Work in Compressed Air" which form part of the overall project health & safety plan. The content of this document is normally provided by key project personnel, who will assist the "Principle Compressed Air Contractors" in control, to produce the overview, operational requirements and method statements. This will normally be coordinated by the "project hyperbaric technical consultant" with specialist hyperbaric clinical & occupational health input from the contract medical advisor, plus technical data from specialist equipment suppliers. In particular, the hyperbaric technical consultant and contract medical advisor must interact to ensure that all medical, health safety and operational issues are adequately covered. The whole document should be "engineered" to produce the safest and most efficient working package in line with project needs, whilst remaining fully compliant with legislative guidance. The document itself defines the operational, clinical and health parameters to be observed, training programmes, emergency actions, equipment standards and planned methods of work. It also defines clear areas of responsibility for all parties involved, which also implies legal responsibility thus supporting the principle compressed air contractor, who holds overall responsibility.
In terms of practical application of compressed air on site, close interaction of the contractors’ person in control, contract medical advisor and site hyperbaric operatives (MLA’s) is essential. Between them, they are responsible for insuring that the procedures designed are closely observed, and where necessary updated or amended according to projects needs and conditions, which often are not static. This ensures that the compressed air workforce, project management, client and legislative bodies alike are all fully aware of the designed procedure and protocol, potential risk, control methods and lines of reporting. In particular adequate training and instruction of the compressed air workforce with regular update is essential. If the workforce is confident about the procedures, training, equipment, hyperbaric/medical/project management it will perform safely. If this is not ensured, risk factors will increase, confidence will cease and project efficiency will undoubtedly suffer.
To this end, the UK legislation has now ensured that only qualified, experienced and competent personnel, familiar with modern tunnelling practice can provide hyperbaric advice, give medical cover and operate systems on compressed air tunnel projects. It is no longer adequate to draw on medical cover from either "General Practices" in the locality or from those that have had peripheral involvement in the past. Likewise, the personnel operating the systems on site must be trained, experienced professionals and fully capable of discharging all the requirements specified under modern regulations. Contract Medical Advisors can no longer obtain comprehensive approval to provide cover, but must be appointed by HSE on a project specific basis, based on relative modern industrial experience and qualification. Likewise hyperbaric site personnel (medical/lock attendants – compressor attendants) must have documented formal qualifications, experience and proven ability to meet the legally defined competence standards.
With TBM maintenance programmes being the most common use of compressed air in current modern application, the question of how operational and medical cover is provided is often raised because of the intermittent and unpredictable nature of its use. Increasingly the duties of the Contract Medical Advisor & Site Hyperbaric Personnel are expanding and interlinking to cover all site occupational health safety and medical issues, complimented by expanded relevant qualification and experience. Often the qualification and abilities of these personnel facilitates other areas of essential site cover very easily, meaning that a much larger spectrum of health cover is provided whilst retaining immediate operational readiness for compressed air. This removes the headache of constant re-mobilisation for compressed air, provides continuity and leaves lines of reporting uncompromised.
Where more traditional compressed air applications are required, involving longer periods of continuous pressurised work, obviously more consideration has to be given to providing continuity and necessary cover specifically for compressed air. Issues such as maintaining medical fitness, maintenance of systems, data collation and number of personnel required can all be catered for in the overall project risk and operational assessment.
Conclusion & Outlook
Intrinsically, all tunnelling activities remain comparatively high risk against other construction, the application of compressed air to assist a particular process compounding this risk further. When the idiosyncrasies of hyperbaric environments and human physiology are also taken into consideration it would be a brave man that would state that compressed air tunnelling is, or can ever be completely safe. However, the advancement of hyperbaric technology and associated medical understanding and awareness when included in modern legislative guidance and site practice, should very soon make it possible to state that it will only be undetectable human physical effects or rare equipment failure which present the main potential hazards. Both these being present in the analysis of any industry or activity, both representing minimal risk.
Outside of the UK, transition in compressed air technology and operating practice has also been taking place. Indeed in Europe oxygen assisted decompression techniques have been available for some time. As a result, some operators in Europe have reviewed compressed air practice in the UK as being backward and out of touch. There might be some justification in saying that the transition has been slower, but this has been integral in the review process of UK practice. The 1996 regulations in original format intended the introduction of oxygen assisted decompression at some stage, but only after careful review of all the associated risks from using oxygen below ground, its attributes in assisting decompression never being in doubt. Following research by the HSE and industry consultation, amendments were made under the 1996 Compressed Air Regulations in September 2001, making oxygen assisted decompression compulsory in the UK, with a continuing research programme to improve decompression procedure and tunnel safety. As with all new systems time to familiarise, collect and evaluate data will be required before a full appraisal is made. The introduction of the new legislation, and all its aforementioned inclusions, have certainly now set the scene for the UK to have the safest, most comprehensive systems for pressurised tunnel work and management, with commitment to further development.
