Dive computers are essential tools to ensure the safety of divers. However, their software is not certified, despite the « CE » marking that can be misleading. This marking is actually limited to pressure and time measurement sensors. Let’s take a closer look at the regulations governing these devices.
General Framework of Regulation
EU Regulation 2016/425 requires the « CE » marking for personal protective equipment (PPE) marketed, loaned, or rented within the European Union. This regulation aims to ensure the health and safety of users while ensuring the free movement of compliant PPE. Member States cannot hinder the availability of this equipment.
CE Marking: Limited to Pressure and Time Measurement
Depth gauges and instruments combining depth measurement and automatic timing are considered diving accessories, subject to the NF EN 13319 standard. The precision requirements are strict:
- Time measurement error: must not exceed +/- 1 minute over 120 minutes.
- Pressure measurement: tolerance varies with depth, ranging from -0.04 bar to +0.08 bar at 3 m, to -0.15 bar to +0.10 bar at 60 m.
Do Not Confuse Pressure and Depth
Diving instruments measure pressure (atmospheric pressure + water pressure) using a piezoelectric sensor. This process involves several factors:
- Atmospheric pressure: generally set at 1 bar or 0.95 bar for dive tables.
- Total pressure: may slightly vary depending on each sensor, which is usually supplied with its calibration curve.
- Water density: depends on salinity and temperature, which can change during a dive.
Examples of Depth Calculation
Let’s take an example with a pressure of 6 bars:
- Atmospheric pressure at 1 bar: displayed depth = 5 bars of water = 50 meters.
- Atmospheric pressure at 1.03 bar: displayed depth = 4.97 bars of water = 49.7 meters.
- Density at 1.02 bar/liter: displayed depth = 48.7 meters.
- Density at 1.035 bar/liter (seawater): displayed depth = 48.01 meters.
Thus, for the same pressure, the depth displayed by a dive computer can vary by 1 to 2 meters. This highlights the importance of not blindly relying on device readings.
Non-Standardized Software
The NF EN 13319 standard specifies that any information related to decompression obligations is excluded from its scope. Therefore, the software of dive computers is not standardized, which can lead to significant variations in results from one device to another.
Successive Dives
The Haldane model, used by most dive computers, is designed for a single dive within 24 hours. For multiple dives, it is up to the manufacturer to determine the algorithm to apply. Dive computers are divided into three categories:
- Category 1: Integrate an additional algorithm for successive dives (e.g., Suunto, Scubapro, Aqualung).
- Category 2: Claim to be « pure Haldanian » without additional algorithm (e.g., Shearwater, Garmin).
- Category 3: Apply arbitrary penalties by gradient factors (e.g., Sirius model from Mares).
Non-Compliant Cases
Rapid ascents, yo-yo dives, and interruptions of safety stops increase the risk of decompression accidents, but these situations are not modeled. Divers must therefore be vigilant and follow appropriate protocols based on their training.
Conclusion
The lack of standardization in decompression calculations should prompt divers to question their choice of dive computer and the procedures to adopt, always remaining responsible for their safety.
This article, originally written by Alain Foret for our print edition, has been adapted for the web.
Photos: Nicolas Barraqué.
Sources
Art. 7, EU Regulation 2016/425.
A. A. Bühlmann, E. B. Vollm, P. Nussberger, Diving Medicine, Springer-Verlag Berlin Heidelberg 1990, 1993, 1995, 2002, p. 165 in the 2002 edition.
Standard NF EN 13319.
Haldane J.-S. et al., The Prevention of Decompression Air Illness, J. Hyg., 1908, pp. 369-370.
A. A. Bühlmann, Behavior of Dive Computer Algorithms in Repetitive Dives: Experience and Needed Modifications, in Hamilton R. W., The Effectiveness of Dive Computers in Repetitive Diving, Undersea and Hyperbaric Medical Society, Inc, 1995.
Sirius User Manual (Mares), p. 13.
Foret A. and Frasquet E., Dive Computers and the Absence of Over-Penalization in Successive Dives, Worldivers, ResearchGate, Dec. 2023.
See the training book series Diving Pleasure, A. Foret, Éditions GAP.