From UPTD to ESOT: Monitoring hyperoxic exposure in surface-oriented diving

Area of Science:

• Diving Medicine
• Hyperbaric Physiology
• Toxicology

Background:

• Pulmonary oxygen toxicity (POT) is a risk in diving, necessitating accurate exposure monitoring.
• Current metrics like Unit Pulmonary Toxic Dose (UPTD) have limitations.
• A proposed metric, K (t² x pO₂), offers improved accuracy but is complex for operational use.

Purpose of the Study:

• To introduce and validate a new, practical metric for assessing hyperoxic exposure in diving.
• To propose Equivalent Surface Oxygen Time (ESOT) as a replacement for UPTD and K.
• To evaluate ESOT's accuracy and operational utility in predicting POT.

Main Methods:

• Defined ESOT as t x pO₂ (t in minutes, pO₂ in atm), with ESOT=1 representing 1 minute of 100% O₂ at surface pressure.
• Compared ESOT's practicality and accuracy against UPTD and K for POT prediction.
• Translated existing hyperoxic threshold limits into ESOT values.

Main Results:

• ESOT provides a more practical and intuitive measure of hyperoxic exposure compared to K.
• ESOT maintains accuracy in POT prediction, comparable to existing metrics.
• Established ESOT thresholds for daily hyperoxic limits: 650 for two days, 500 for five days, and 420 for unlimited days.

Conclusions:

• ESOT is a superior metric for operational hyperoxic exposure monitoring in diving.
• ESOT simplifies the interpretation of exposure levels, analogous to UPTD.
• The proposed ESOT metric enhances safety and practicality in managing POT risks during diving operations.