In practice, many divers use their scrubber over several dives. Once charged, they note the operating time - and store the scrubber until the next use. Sounds logical, doesn't it?

But a study by Pollock et al. (2018) shows: This is riskier than many people think. And the crucial processes do not take place visibly, but quietly - inside your limescale container.

The scrubber - i.e. the container with breathing lime (usually Sofnolime 797™) - is the heart of every rebreather. Its task is to chemically bind CO₂ from the exhaled gas before it returns to the diver.

This works via a multi-stage reaction with sodium and calcium hydroxide:

1.  CO₂ reagiert mit Wasser und bildet Kohlensäure.

2.  Diese reagiert mit Natriumhydroxid und wird zu Natriumkarbonat.

3. Dieses wiederum reagiert mit Calciumhydroxid – übrig bleibt: Calciumkarbonat (Kalkstein), Wasser und Wärme.

How strongly does the type of storage influence the subsequent CO₂ absorption performance of an already used scrubber?

To do this, they packed the lime into an Evolution Plus™ rebreather system under realistic conditions, operated it for 90 minutes under a controlled CO₂ supply and then stored the scrubbers under three conditions:

1. Offen an Luft (für 28 Tage)

2. Luftdicht vakuumversiegelt (ebenfalls 28 Tage)

3. Offen, aber nur über Nacht

After the storage period, the canisters were returned to the test system - and continued to run until the CO₂ content of the breathing air reached 1 kPa (critical breakthrough value).

Open storage - 28 days

Average running time after storage: 188 minutes

→ Significantly reduced performance

Sealed storage - 28 days

Average running time: 241 minutes

→ Almost full capacity retained

Open overnight

Average: 239 minutes

→ No significant impairment

In other words:

Stored open = 53 minutes shorter operating time

Or: 100 liters less CO₂ absorbed

Das ist nicht nur ein technischer Unterschied. This is a security gap.

Note: Die oben genannten Laufzeiten stellen keine Empfehlung dar. Die Untersuchung wurde unter Laborbedingungen durchgeführt und diente ausschließlich dem Zweck, Rückschlüsse auf die bestmögliche Lagerung von Kalk zu gewinnen – nicht, um die maximale Laufzeit von Kalk zu ermitteln.

The exact causes are complex, but there are two main hypotheses:

1. Reaktion mit Luftfeuchtigkeit:

Air contains CO₂ (albeit little) and moisture. Breathing lime stored openly continues to react - slowly but constantly. The chemical conversion is ongoing. This reduces the subsequent capacity.

2. Austrocknung:

The reaction only works with water. If the lime dries out - for example in air-conditioned rooms with low humidity - it loses its efficiency.

Paradoxically, too much or too little moisture can therefore be a problem.

In the test, the humidity was around 53 %. In drier rooms (winter, air conditioning, heated drying cellar?) the effect could be even greater.

If you have a partially used scrubber:

✅ Avoid open storage for several days.

✅ Use vacuum bags or airtight containers.

✅ Use Scrubber as soon as possible after packing.

✅ If you store overnight, "open" is fine - but here too: better airtight.

✅ If in doubt: replace the filling. A new filling may cost you 20 €, but a CO₂ breakthrough is priceless - in the worst case with your life.

 • „Der Scrubber ist doch nicht nass – da kann nichts passiert sein.“

→ Wrong. Hygroscopy means: even the air is enough.

• „Ich lager das im Rebreather mit verschlossenen Stopfen.“

→ Sounds good, but blind plugs are not airtight. And there is often residual moisture in the appliance.

• „Ich merk doch, wenn der Kalk verbraucht ist.“

→ No. The rise in CO₂ comes on gradually. By the time you feel it, it's often too late - or you confuse the symptoms with stress, cold or tiredness.

A scrubber does not store energy on demand. It is a chemical system that reacts as soon as it is activated. This activation happens not only during diving, but also during storage - quietly, invisibly and irreversibly.

Remember:

What looks dry may have been used up long ago.

And: safety doesn't start when you descend, but when you pack.

Are you traveling with the rebreather for several days at a time? Then overnight storage is crucial. The study shows that storing it open overnight is not critical - but the same applies here: protect it airtight if possible.

Source:

Pollock NW, Gant N, Harvey D, et al. Storage of partly used closed-circuit rebreather carbon dioxide absorbent canisters. Diving and Hyperbaric Medicine. 2018;48(2):96–101.