Survival suit volume reduction associated with immersion: implications for buoyancy estimation in offshore workers of different size.

Rationale: It is currently unknown how body size affects buoyancy in submerged helicopter escape.

Method: Eight healthy males aged 39.6 ± 12.6 year (mean ± SD) with BMI 22.0-40.0 kg m wearing a standard survival ('dry') suit undertook a normal venting manoeuvre and underwent 3D scanning to assess body volume (wearing the suit) before and after immersion in a swimming pool.

Results: Immersion-induced volume loss averaged 14.4 ± 5.4 l, decreased with increasing dry density (mass volume) and theoretical buoyant force in 588 UK offshore workers was found to be 264 ± 46 and 232 ± 60 N using linear and power functions, respectively. Both approaches revealed heavier workers to have greater buoyant force.

Discussion: While a larger sample may yield a more accurate buoyancy prediction, this study shows heavier workers are likely to have greater buoyancy. Without free-swimming capability to overcome such buoyancy, some individuals may possibly exceed the safe limit to enable escape from a submerged helicopter. Practitioner Summary: Air expulsion reduced total body volume of survival-suited volunteers following immersion by an amount inversely proportional to body size. When applied to 588 offshore workers, the predicted air loss suggested buoyant force to be greatest in the heaviest individuals, which may impede their ability to exit a submerged helicopter.