H&S - COMPRESSED AIR WORK | INSIGHT


Table 1: Screening for dysbaric osteonecrosis (DON) – Common Misconceptions Myth


‘Oxygen decompression has eliminated DON’


Reality


Although rates of the condition are likely to have been significantly reduced with the implementation of oxygen decompression, there is currently no evidence to confirm the elimination of DON in UK CAW.


‘We don’t get DON cases in our CAW using oxygen decompression’


Early DON lesions are generally asymptomatic to the worker and can only be reliably detected by MRI screening of long bones. Any affected worker may not develop problems for several months or years. Project staff will be unlikely to know of such problems. Late presenting DON lesions appear as non-specific to the occupational cause and so are easily missed by hospital doctors. These factors lead to DON being potentially under-recognised, under-reported and under-diagnosed in the compressed air workforce.


‘The magnetic field used in MRI is dangerous’


Provided safety considerations relating to ferromagnetic metals are adhered to, exposure to the magnetic field used in MRI is considered to be completely safe.


‘MRI is too expensive’


Health surveillance based on appropriate risk assessment and controls is a legal requirement in the UK. The cost of MRI has reduced significantly over time, and is now considered to be comparable to the cost of historical long bone X-ray studies. Any cost-benefit analysis of screening should consider potential cost of future litigation in the event of a missed diagnosis, as well as the burden of morbidity.


‘MRI is too complicated to use for health surveillance for DON’


‘MRI is not accurate enough to detect lesions’


MRI has been successfully used on multiple projects for health surveillance of DON in since 2007.


Multiple studies have demonstrated MRI to be the most accurate imaging modality for osteonecrosis. Early lesion detection is a particular strength, making it more powerful as a health surveillance tool in a typically transient workforce.


‘MRI shouldn’t be used as it may pick up other abnormalities’


MRI is a highly sensitive imaging modality, and therefore the detection of other adverse findings may occur during routine screening. With appropriate interpretation and counselling of the worker, these can be managed appropriately.


When the potential risks of undetected DON and the efficacy of MRI for its early detection are explained,


‘The workforce won’t understand or accept MRI long bone screening’


experience shows that the vast majority of CAW make an informed choice to proceed with long bone MRI screening. The workers appreciate knowing that they will have confirmation (positive or negative) of any post exposure DON and that any further CAW can be undertaken safely. All workers can decline the offer of MRI screening after individual counselling by the Contract Medical Advisor or HSE Appointed Doctor for Compressed Air Work.


in compressed air workers when using modern decompression protocols, including oxygen or mixed gas techniques. With modern CAW extending towards higher working


pressures and the adoption of mixed gas and saturation techniques17


, monitoring of compressed air workers for


adverse health effects remains critical. Enhanced medical surveillance of the exposed


workforce is accepted practice within the diving industry whenever new decompression schedules are developed, or adopted from different work environments (such as diving to compressed air work)18


. This helps to inform


the overall safety performance when being used under ‘real-life’ hyperbaric tunnelling conditions. This ‘precautionary’ approach should be applied


when any new or adapted decompression table is first being used under hyperbaric tunnelling conditions, this includes bone screening when deemed appropriate.


HEALTH SURVEILLANCE AND THE ROLE OF MRI Historically, radiographic skeletal surveys were used to screen for bone lesions, but X-rays may not detect DON until 5-6 months after the incident exposure,


leading to a high false negative rate9


. Additionally, the


incurred radiation exposure is undesirable, leading to its deselection for screening. In recent years, MRI has emerged as the superior


imaging modality for DON detection. Unlike X-ray, MRI: ● Detects early-stage lesions within days of exposure9,19 ● Avoids ionising radiation risks20


; and,


● Is highly accurate in the detection of osteonecrosis, with a sensitivity and specificity of >99%21


.


Studies in which MRI has been used for screening for DON, including those directly comparing MRI and X-ray, consistently favour MRI which has been recommended for screening in divers22, 23


. Cost and availability were originally significant


barriers to adoption. However, inflation adjusted costs have reduced by approximately two-thirds since the early 2000s, and private providers now offer MRI services on a nationwide basis24


. One UK Contract


Medical Advisor has offered MRI screening to all exposed compressed air workers at risk of DON on multiple UK CAW projects 2008–2025. This has been successful and the reported experience is that MRI presents a feasible screening tool for this condition25


. July 2025 | 33 ;


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