H&S - COMPRESSED AIR WORK | INSIGHT


Early detection in individuals after compressed air


work exposure facilitates occupational restriction of those affected from further hyperbaric exposure to prevent progression of bone disease, as well as earlier investigation and treatment. Data from workforce bone screening programmes


also facilitates health and safety evaluation of the relevant decompression schedule. Screening, when confirmed as negative, also benefits the employer in protecting from future litigation due to the erroneous attribution of lesions arising from a specific project. Historically, cases have been brought against employers for significant sums of money in civil courts. Adequate medical monitoring of the compressed air


workforce is a legal requirement under the Work in Compressed Air Regulations 19961


: . UK health and safety


legislation also mandates health checks or screening to identify work-related ill health, known as health surveillance, where there is2


1. An identifiable work-related disease; 2. A reasonable likelihood of occurrence under specific work conditions; and,


3. A valid, low-risk screening method. DYSBARIC OSTEONECROSIS:


For many years there has been considerable discussion within the BTS Compressed Air Working Group (BTS CAWG) regarding this important UK tunnelling industry health and safety issue. This debate boils down to two key questions: does DON still pose a significant risk to today’s compressed air workforce with improved decompression procedures? If so, is magnetic resonance imaging (MRI) a suitable tool for monitoring for DON as part of health surveillance of the exposed workforce? To better understand this area, the BTS recently


sponsored the author to undertake an MSc dissertation at the University of Manchester to systematically review the current published literature regarding the efficacy of MRI as a screening tool for the early detection of DON, with a view to informing health surveillance practice in UK compressed air work.


BACKGROUND Compressed air work (CAW) has long been an integral part of tunnelling, historically involving pressurisation of entire tunnel sections to maintain a dry excavation environment. In this context, gauge pressure (bar(g() is used, i.e. the amount by which pressure in a compressed air environment exceeds normal atmospheric pressure. Workers transitioned between surface pressure and the hyperbaric atmosphere via air locks before then engaging in often physically demanding tasks at pressures ranging from 0.70 bar(g) to 1.5 bar(g), up to a maximum of 3.45 bar(g). This required a large workforce of compressed air workers, typically numbering into the hundreds on bigger projects. During this period,. The decompression safety of these


was limited by the technology of the time and was often not implemented optimally on-site. With these exposures, musculoskeletal decompression sickness


PATHOPHYSIOLOGY AND RISK FACTORS DON refers to bone necrosis (tissue death) caused by hyperbaric exposure, primarily affecting compressed air workers and divers. During exposure, increased pressure dissolves greater quantities of inert gas, typically nitrogen, into bodily tissues. Rapid decompression can lead to supersaturation and bubble formation. These bubbles can disrupt the blood supply within bone marrow, leading to necrosis4


. The primary risk factors for DON are well documented


and include: ● Cumulative pressure exposure: A higher number of decompressions increases risk5,6


;


● Maximum pressure exposure: Higher pressures correlate with increased DON incidence7


;


● Exposure duration: Extended work periods (>4 hours) elevate risk7


;


● Decompression rate: Rapid decompression increases risk; and,


● Decompression sickness (DCS) history: DON is significantly correlated with previous decompression sickness (‘joint bends’). 10% of DCS cases develop DON and 25% of DON cases having a prior history of DCS8


.


In compressed air workers, DON most commonly affects the humeral and femoral bones, including parts of the shoulder and hip joints respectively9 individuals commonly have multiple lesions10 Boney shaft lesions may not result in any skeletal


. Affected .


symptoms, however problematic joint lesions often remain asymptomatic for years before the development of joint pain and stiffness. This can lead to severe functional impairment, often necessitating joint replacement of the affected shoulder or hip.


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(‘joint bends’), and dysbaric osteonecrosis (DON), colloquially referred to as ‘bone rot’, were common in workers. Adoption of the Blackpool air decompression


tables in the 1970s and changes in management of compressed air work throughout the 1990s, assisted by the implementation of the Work in Compressed Air Regulations 19961


and the statutory requirement


for staged oxygen decompression from 2001, have significantly improved decompression safety3


. In


combination, these changes have led to an apparent decrease, but not elimination, of such pressure-related illness. The widespread adoption of tunnel boring


machines (TBMs) has significantly reduced the number of individuals required for tunnel construction, and therefore the compressed air workforce and number of compressed air work exposures. However, hyperbaric interventions for TBM cutterhead maintenance still require shifts of 3-5 trained personnel to work under pressure to cover the TBM maintenance requirement.


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