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A mini scuba tank holds air compressed to 200 bar. The main danger does not come from the tank itself: it comes from the way you breathe underwater and the way you refill it. Here is what we know, with sources to back it up. To see the full range, visit our mini scuba tank shop<\/a>.<\/p>\n OXSEA mini dive tanks are made of 6061 aluminium and have a working pressure of 200 bar. The OX500 and the OX500Plus hold 0.5 litres, the OX1000 holds 1 litre (our comparison of the three models<\/a> sets out how they differ). They undergo leak and reliability testing.<\/p>\n The pressure gauge (built into the OX500, external and supplied with the OX500Plus) shows the pressure while you refill. The safety disc, a protective device, can be replaced by following a video tutorial.<\/p>\n Underwater, the air you breathe is at the same pressure as the water around you. As you rise, the pressure drops and that air expands: if you breathe normally, it escapes. If you hold your breath, it overstretches your lungs until it injures them. This is lung overexpansion injury (pulmonary barotrauma), which can send air bubbles into the bloodstream (gas embolism).<\/p>\n Shallow water is no protection. DAN (Divers Alert Network), an international organisation devoted to diver safety, points out that lung overexpansion can happen in a swimming pool, and that rising about 1.5 metres while holding your breath can be enough to cause a gas embolism. The relative change in pressure is greatest near the surface: between 3.4 metres and the surface, air held in the lungs gains a third in volume.<\/p>\n After any time underwater, chest pain, even if it starts several hours later, means you should call for help: 112, the European emergency number, or your local emergency number. DAN reports the case of an experienced diver who stayed shallower than 5 metres, felt this pain the same evening and was sent to the emergency department.<\/p>\n The freediver’s habit of surfacing with full lungs becomes dangerous with compressed air. In the journal Diving and Hyperbaric Medicine (2019), a hyperbaric physician and a dive safety specialist describe the death of a 26-year-old freediver who had breathed from a diving friend’s regulator at around 10 metres before surfacing. Their conclusion: a freediver who breathes compressed air at depth runs the same risk of lung overexpansion and gas embolism as a scuba diver if they do not breathe out enough on the way up. They note that gas embolism has occurred from as shallow as one metre. Never take a breath from the tank at the bottom and then surface holding it.<\/p>\n You will breathe whatever air you put in the tank. DAN lists several sources of contamination: carbon monoxide from exhaust fumes or from overheating compressor oil, hydrocarbons from lubricants, dust, and moisture, which also promotes corrosion. Carbon monoxide has no smell and no taste.<\/p>\n The manual pump<\/a> (0.5 litre tanks only) and the 12V mini compressor<\/a> are fitted with filters. These are consumables: replace them regularly.<\/p>\n According to DAN, more than 90% of cylinder ruptures happen during filling. Repeated fills close to the test pressure (which is higher than the working pressure), or beyond it, end up deforming the cylinder, which can then no longer withstand even its working pressure.<\/p>\n According to DAN, a cylinder with corrosion or visible damage should not be used. Changing the filters, the safety disc or the regulator seal, and checking for leaks, are all shown in our OXSEA School video tutorials<\/a>. For an inspection or a repair, contact us<\/a>.<\/p>\n Full-size scuba tanks are generally subject to periodic inspection and retesting, at intervals set by national rules that differ from one country to another.<\/p>\n Whether those rules also apply to small cylinders of 1 litre or less depends on the country. Our tanks hold 0.5 litres or 1 litre, at a working pressure of 200 bar: check the rules that apply where you live and where you fill your tank.<\/p>\n Whatever the local rules say, we recommend having the tank checked periodically by a professional, at a pace that suits how much you use it, and inspecting it yourself at every refill.<\/p>\nHow our tanks are designed<\/h2>\n
The real danger: holding your breath on the way up<\/h2>\n
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Breath-hold diving and compressed air: never mix the two<\/h2>\n
Clean air when you refill<\/h2>\n
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Care and inspection: good habits<\/h2>\n
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Periodic inspection: check the local rules<\/h2>\n