Decompression diving is the most demanding discipline in recreational and technical diving. When dives exceed no-decompression limits, ascent must be carefully controlled through staged stops to allow dissolved nitrogen to safely leave the body. Getting it wrong means decompression sickness (DCS) — potentially fatal.
This comprehensive guide covers everything technical divers need to know about decompression for 2026: dive tables, computer algorithms, planning software, and safety protocols for depths beyond 40 meters (130 feet).
⚠️ Critical Safety Warning
Decompression diving requires specialized training, equipment, and experience. This guide is for educational purposes only. Never attempt decompression diving without proper certification (TDI, IANTD, GUE, or NAUI Technical), redundant equipment, and a qualified dive buddy.
📊 Key Statistic
Decompression sickness incidence increases exponentially with depth and bottom time. At 30 meters (100 feet) within NDL limits, DCS risk is ~0.01% per dive. At 60 meters (200 feet) with 20 minutes bottom time, risk increases to ~2-5% per dive — 200-500x higher.
📊 Understanding Decompression
During a dive, inert gas (nitrogen) dissolves into body tissues under pressure. On ascent, pressure decreases and dissolved gas must be eliminated via the lungs. Too rapid ascent allows bubbles to form — causing decompression sickness.
Tissue Compartments
Decompression models divide the body into hypothetical tissue compartments with different gas uptake/elimination rates (half-times):
- Fast Tissues (1-5 minute half-times): Blood, brain, spinal cord — absorb/release gas quickly
- Medium Tissues (5-20 minutes): Muscles, organs — intermediate rates
- Slow Tissues (20-80+ minutes): Bone, cartilage, tendons, fat — absorb/release slowly (liability tissues)
📋 Decompression Tables
Traditional decompression planning using printed tables — still used as backups to computers.
US Navy Dive Tables (most common)
- Based on Haldanean model with tissue compartments from 5-120 minutes
- Conservative (safe) but limited to air diving
- Requires precise depth/time tracking — no "profile following"
Bühlmann ZHL-16 Tables
- Based on the most widely used algorithm in dive computers
- More aggressive than US Navy — allows longer bottom times
- Gradient factors allow customization (GF 30/70 typical for technical diving)
BSAC 88 Tables
- Used by British Sub-Aqua Club
- Conservative, popular in UK/Europe
📖 Table Reading Example (US Navy)
Dive to 150 feet (45 meters) for 20 minutes:
- Pressure group from Table 1: O
- Required decompression from Table 2: 8 minutes at 20 feet (6 meters), 16 minutes at 10 feet (3 meters)
- Total ascent time: ~25 minutes plus travel time
💻 Dive Computer Algorithms
Modern dive computers use real-time depth/time data to calculate decompression dynamically — allowing multi-level diving and gas switching.
Bühlmann ZHL-16C — Industry Standard
- Created by Dr. Albert Bühlmann, University of Zurich
- Most widely implemented algorithm (Shearwater, Suunto, Scubapro, Oceanic)
- 16 tissue compartments with half-times from 4 to 635 minutes
- Uses gradient factors to control conservatism
RGBM (Reduced Gradient Bubble Model) — Suunto, Oceanic
- Bubble-based model vs. dissolved gas (traditional)
- Accounts for microscopic bubble formation
- More conservative on repetitive dives
- Suunto Fused RGBM is current standard
VPM-B (Varying Permeability Model) — Tech/CC divers
- Advanced bubble-mechanics model
- More aggressive than Bühlmann for deep/short dives
- Requires validation — not for beginners
📊 Algorithm Comparison Table
| Algorithm | Model Type | Conservatism | Best For | Popular Computers |
|---|---|---|---|---|
| Bühlmann ZHL-16C | Dissolved gas | Adjustable (GF) | All technical diving | Shearwater, Ratio, Heinrichs Weikamp |
| Suunto Fused RGBM | Bubble/dissolved hybrid | Moderate-High | Recreational, multi-day | Suunto Eon, D-series |
| VPM-B | Bubble mechanics | Low (more aggressive) | Deep/short decompression | Shearwater (fw 84+), custom firmware |
| DSAT (PADI) | Dissolved gas | Low | Recreational (NDL only) | PADI compatible computers |
| Ratio iX3/MDM | Hybrid | Adjustable | Tech/CCR | Ratio, Deco software |
🏆 Recommended: Shearwater + Bühlmann ZHL-16C with Gradient Factors
For technical diving, Shearwater dive computers (Perdix, Teric, Petrel) running Bühlmann ZHL-16C are the industry gold standard. Set gradient factors to GF 30/70 for open circuit tech, GF 50/80 for recreational, or GF 20/85 for very deep trimix. Customizable and proven safe in thousands of technical dives.
🔄 Gradient Factors (GF) Explained
Gradient factors are a modification to the Bühlmann algorithm that control conservatism at the deep and shallow ends of the decompression profile.
- GFlow (deepest stop): Controls first stop depth (lower GF = deeper first stop = more conservative)
- GFhigh (surface): Controls final surfacing M-value (lower GF = longer shallow stops = more conservative)
- Common settings: GF 30/70 (conservative tech), GF 50/80 (moderate tech), GF 40/85 (deep/short)
- Recreational default: GF 45/95 or equivalent (pre-programmed)
📱 Dive Planning Software
MultiDeco (Windows/Mac) — Gold Standard
- Professional dive planning software ($49/year)
- Supports Bühlmann, VPM-B, RGBM, US Navy
- Gas switching, trimix, CCR support
- Used by technical divers, instructors, military
Subsurface (Open Source — Free)
- Created by Linus Torvalds (of Linux fame)
- Supports Bühlmann and VPM-B
- Desktop and mobile versions
- Best free option — excellent gas integration
DecoPlanner (Shearwater Cloud)
- Free with Shearwater computers
- Syncs directly with dive log
- Export to MultiDeco if needed
🛡️ Decompression Stops & Ascent Protocols
Deep Stops (1/2 of max depth)
Example: 60m dive → deep stop at 30m (1/2 max depth) — controversial (some research suggests increases bubble load). Many agencies now skip deep stops except for trimix.
Primary Decompression Stops (GF Low determined)
- Computer-calculated — typically 9, 6, 3 meters (30, 20, 10 feet)
- Each stop length determined by algorithm
- Missed stop = significant DCS risk
Oxygen (O2) Stops
- At 6m (20ft) switch to 100% O2 via deco bottle
- Reduces decompression time by 30-60%
- Requires proper gas planning, O2 cleaning, and training
📋 Minimum Deco Ascent Protocol
1. Ascent rate: 9-10 meters per minute (30 ft/min) to first stop
2. Execute all stops precisely (± 0.5 meters, ≤ schedule time)
3. Longer is safer, shorter is dangerous
4. Safety stop at 5-6m (15-20ft) regardless of algorithm (3-5 minutes)
5. Final ascent from last stop to surface: 1 meter/minute
🩸 Decompression Sickness (DCS) — Signs & Protocols
DCS Type I (Pain only / Skin)
- Joint pain (elbow, shoulder, knee) — "the bends"
- Skin rashes/mottling (cutis marmorata)
- Fatigue, itching
- Treatment: In-water recompression (controversial) or chamber
DCS Type II (Neurological)
- Numbness, tingling (paresthesia)
- Dizziness, vertigo (stagger)
- Blurred vision, hearing loss
- Paralysis, difficulty urinating
- EMERGENCY — immediate evacuation to hyperbaric chamber
🚨 DCS Emergency Protocol
1. Administer 100% oxygen (demand valve / non-rebreather)
2. Hydrate (oral fluids if conscious)
3. Contact DAN Emergency Hotline: +1-919-684-9111 (global)
4. Locate nearest hyperbaric chamber
5. Monitor vitals — neurological symptoms may worsen
6. Do not re-dive (in-water recompression is controversial and dangerous without training)
🧮 Gas Planning for Decompression Dives
Rule of Thirds (Open Circuit, Single Decompression Cylinder)
- 1/3 down, 1/3 up, 1/3 reserve
- Requires larger cylinders (e.g., twinset 2x12L, 2x15L)
Rock Bottom Gas Planning (Preferred)
- Calculate gas needed for buddy to ascend from max depth including decompression
- Minimum "turn pressure" established before descent
- More conservative and realistic than Rule of Thirds
Decompression Gas (50%, 100% O2)
- Carried separately (stage/deco cylinder)
- Switched at shallow stops (typically 21m/70ft for 50%, 6m/20ft for 100% O2)
- CNS oxygen toxicity risk limits 100% O2 depth (max 6m/20ft partial pressure)
🧊 Technical Equipment Requirements
| Equipment | Recreational | Technical Deco | Required |
|---|---|---|---|
| Cylinders | 1x single | Twinset + stage(s) | Redundancy |
| Regulators | 1 first/2 second | 3-5 first stages | Redundancy |
| Buoyancy | BCD | Wing + backplate | Stability, trim |
| Computer | Single | 2x (backup computer) | Redundancy |
| Decompression Cylinder | None | 1-2 (50%, 100% O2) | Accelerates deco |
| Dive Light | Optional | 2x (primary + backup) | Depth/overhead |
| Cutting Device | 1 | 2+ (line cutter, shears) | Entanglement risk |
🛡️ Redundancy Requirement
Technical decompression diving requires full redundancy: Two computers (or computer + bottom timer/backup), two independent gas sources beyond 40m, two cutting devices, two lights, and two first stages per diver. DCS without redundancy is life-threatening.
🏆 Recommended Dive Computers for 2026
- Shearwater Perdix 2 / Teric: Best tech computer. Bühlmann GF, air integration, robust, $1,000-1,200
- Garmin Descent Mk3i: Excellent recreational/light tech, $1,200-1,600
- Ratio iX3M Tech+: Full tech features, multiple algorithms, $900-1,200
- Suunto Eon Steel: Fused RGBM — conservative, reliable, $1,100
- Shearwater Petrel 3 (Chest mount): For CCR or drysuit, $1,100
📝 Final Recommendations
- Get certified: TEC 40/45/50 (PADI), Technical Diver (TDI, IANTD), or Fundamentals (GUE)
- Choose algorithm: Bühlmann ZHL-16C with gradient factors (Shearwater computer)
- Plan every dive: Use MultiDeco or Subsurface, share plans with team
- Carry redundant everything: Gas, computer, cutting tools, lights
- Practice emergency drills: Share gas, shutdowns, lost deco gas, lost diver, before every tech dive
Decompression diving is highly rewarding but unforgiving. Master the science, respect the tables, and always plan for the worst while hoping for the best.
Disclaimer: Decompression diving requires specialized training, certification, and experience. This guide is for informational purposes only and does not constitute instruction. Never attempt decompression diving without proper certification and redundant equipment.