What You’ll Learn
As you work through this site, you’ll notice coloured boxes popping up in the margins of our guides and articles. Each one flags a specific type of information — a practical tip, a safety reminder, a real-world story, or a deeper technical explanation you can skip if you’re not in the mood.
Think of them as road signs. Once you know what each one means, you can scan a page quickly and zero in on exactly what’s useful to you. The boxes below show you each callout type exactly as it appears throughout the site, along with a sample so you can see them in action.
The Callout Types
Apply a thin layer of silicone grease to your O-rings before assembly. It only takes a few seconds and dramatically extends their life — plus it makes them much easier to remove next time.
Always perform a negative pressure test on your breathing loop before every dive. A small leak that’s barely noticeable on the surface can flood your scrubber at depth.
Never use pure oxygen at depths greater than 6 metres. At higher partial pressures, oxygen becomes toxic to your central nervous system — and the first symptom is often a seizure with no warning at all.
CO&sub2; absorbent works by chemical reaction, not by filtering. Once the chemical is used up, no amount of airflow will make it work again — it needs to be replaced, not dried out or recharged.
The exothermic reaction between CO&sub2; and calcium hydroxide proceeds as: CO&sub2; + Ca(OH)&sub2; → CaCO&sub3; + H&sub2;O + heat. The water produced is actually beneficial — it helps maintain the humidity needed for efficient absorption in downstream granules.
Analox’s sub-miniature O&sub2; cells are significantly more accurate and longer-lived than standard galvanic sensors. They’re roughly three times the price, but if you’re building an electronic CCR for serious diving, they’re hard to beat.
A length of standard 110mm PVC drainage pipe makes a perfectly serviceable scrubber canister for prototyping. It’s cheap, easy to cut, and available at any builder’s merchant. Just remember it’s not rated for pressure — this is a surface-testing solution only.
If it’s hard to breathe on the surface, it’ll be worse at depth. Never accept high work of breathing as “normal” — find the restriction and fix it before you dive.
In the UK, all compressed gas cylinders must undergo periodic hydrostatic testing in accordance with BS EN 1968 (steel) or BS EN 1802 (aluminium). Using a cylinder with an expired test date isn’t just risky — it’s illegal, and no reputable fill station will touch it.
In 2005, a diver using a home-built SCR experienced a gradual hypoxic blackout at 30 metres. The post-incident investigation revealed that the constant mass flow orifice had been sized using surface-pressure calculations without accounting for depth. The flow rate that delivered a safe mix at 10 metres was dangerously lean at 30. He was lucky — his buddy noticed and got him to the surface.
Quick Reference
Here’s the complete set at a glance. If you see a callout you don’t recognise while reading a guide, you can always come back to this page.
| Icon | Name | What It Means |
|---|---|---|
| build | Tip | Practical advice that saves time, trouble, or money |
| health_and_safety | Safety Note | Routine safety reminder — important but not critical |
| warning | Warning | Serious hazard — stop and think before proceeding |
| lightbulb | Remember | Key fact worth committing to memory |
| science | Technical Stuff | Deeper detail — safe to skip |
| workspace_premium | Premium Option | Higher-end choice with better performance |
| recycling | DIY / Scavenger | Budget-friendly alternative or repurposed part |
| push_pin | Maxim | Golden rule of rebreather building |
| gavel | Legal | Regulatory or compliance information |
| auto_stories | True Story | Real-world anecdote or case study |
Not every guide will use all ten callout types — you’ll only see them where they’re genuinely useful. The important thing is that when one appears, you’ll know exactly what it’s telling you.