What the Data Shows About Open-Circuit Technical Diving Safety (Comparison with CCR Data Analysis)

1. Early OC Technical Diving (1990s–early 2000s)

Unlike CCR, open-circuit (OC) technical diving predates widespread data collection, making exact fatality rates harder to quantify. OC Technical diving mainly evolved through pioneers pushing deep air and early trimix exploration.

However, retrospective analysis from Divers Alert Network (DAN) and early Project Dive Exploration datasets suggests that fatality rates in OC technical diving were significantly higher than recreational scuba.

• Recreational scuba fatality rates during this period:
  👉 ~0.8–1.5 deaths per 100,000 dives
• Technical diving (all categories):
  👉 Estimated ~3–5+ deaths per 100,000 dives (≈3–5× higher than recreational)
• CCR diving for comparison:
  👉 ~4 deaths per 100,000 dives

Many OC incidents were linked to:

• Deep air diving (narcosis-driven incidents and poor decision-making)
• Limited decompression knowledge and tools
• Inconsistent or inadequate decompression and gas planning
• Lack of standardized training

Important context:
This period predates widespread adoption of structured tech training agencies.
Early OC tech diving had a risk profile overlapping early CCR-era risk levels, largely due to experimental practices and inconsistent procedures. OC tech looked simpler, but was often executed in a much less controlled way.

2. Standardization & “DIR Era” (mid-2000s–2015)

This is where things changed dramatically.
With the rise of structured training systems and organizations like Global Underwater Explorers (promoting DIR or “Doing It Right” diving philosophy), or other technical diving agencies such as Technical Diving International (TDI), and IANTD, the safety landscape changed significantly.

What improved:

• Strict gas planning (rock bottom, rule of thirds applied not only to cave diving)
• Elimination of deep air in serious tech diving and widespread use of trimix instead
• Standardized team protocols and equipment (especially in DIR philosophy)
• Better decompression algorithms and computers
• More reliable equipment

Data-backed insight:

DAN reports consistently show technical dives still riskier than recreational, but:
👉 Fatality rates began trending downward relative to early tech diving
👉 Strong relation to trained vs untrained tech divers
👉 Human error remained the dominant factor

A key pattern from DAN analyses shows that most fatalities are caused by violations of known procedures, not unknown risks.

3. Modern OC Technical Diving (2015–Present)

This is where the most interesting comparison to CCR emerges. Recent analyses (DAN annual reports, articles in InDepth Magazine, and conference discussions) suggest that OC technical diving has become significantly safer than it used to be.

Current baseline (context from DAN + global data):

• Recreational scuba:
  👉 ~0.8–1.2 deaths per 100,000 dives
• Technical diving (all types combined, may include CCR influence):
  👉 ~3–5 deaths per 100,000 dives
• CCR diving only:
  👉 ~1.8–3.8 deaths per 100,000 dives

Important nuance: This “technical diving” figure includes CCR, which skews the number upward.

Isolating Open-Circuit Tech Diving (Best Estimate)
When excluding CCR and cave diving (based on DAN incident breakdowns and multiple analyses):

Modern OC tech diving is estimated at ~2–4 deaths per 100,000 dives
➤ Fatality numbers are relatively low compared to total participation (especially in structured environments).

This aligns with:

• Lower or similar risk to CCR
• Higher risk than recreational scuba
• Significant improvement vs early tech era

♠️ Most fatalities cluster in specific scenarios:

• Deep air diving
• Gas switching errors
• Solo diving or team separation
• Hypoxia/hyperoxia (especially with deco gases or hypoxic travel gas)
• Overhead environments
• Inadequate gas planning

Equipment reliability is no longer the main issue. Modern regulators and cylinders are extremely reliable, and failures are overwhelmingly human-factor driven.

Has OC Technical Diving Become Safer?

YES — and more clearly than CCR
Compared to 1990s, the rate of catastrophic unknowns has dropped dramatically. This represents a meaningful reduction in risk.

For comparison:

What improved:

• Standardized training
• Better gas planning and gas management understanding
• Elimination of deep air culture (still could be reduced more)
• Improved team diving philosophy
• Dive planning tools are far more accurate
  
  

OC Tech vs CCR — Side-by-Side Comparison

(*CCR data are from Rebreather Training Council / Rebreather Forum 4)

Although open-circuit technical diving fatalities show a clear decreasing trend compared to earlier periods, current estimates suggest that its fatality rate remains elevated—generally in a similar range to CCR diving, and consistently higher than recreational scuba.

Unlike CCR diving, which cannot realistically be conducted without formal training, open-circuit diving is more accessible and, in some cases, allows divers to “push their limits” without adequate preparation.

Historically, deep air diving was a major risk factor in OC technical incidents. While its use has declined significantly with the adoption of trimix, it has not been eliminated entirely. In contrast, CCR diving is inherently dependent on helium-based diluents for deeper dives, meaning that gas choice is less influenced by cost considerations and more by physiological necessity.

Key Insight

Open-circuit technical diving risk is largely transparent and predictable — driven by gas limits/depletion, decompression issues, and environment. The problems are usually procedural, observable, and often recoverable.

CCR diving risk is often less visible or completely silent/sudden and time-critical — driven by failures in life-support systems (PO₂, loop integrity, CO₂). The risks are rather related to equipment-system complexity.

The research is not only about how often people die, but rather about how those accidents happen. Across all disciplines, the primary critical factor is failure caused by human error.

Important Note

This text is a collection of research data. There is no global database that perfectly separates OC tech from CCR diving. Many “technical diving” statistics include mixed categories (including CCR and cave diving). Fatality rates depend heavily on diver experience, environment, team vs. solo diving, and other factors. Therefore, all OC-specific estimates are informed approximations rather than absolute values. If you have access to more specific research data, we would be happy if you contacted us.

Main sources for this article:

• Divers Alert Network annual reports
• Rebreather Training Council / Rebreather Forum 4
• PubMed (technical diving risk studies)
• InDepth Magazine
• Training agency safety frameworks (GUE, TDI, IANTD)