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Aerorlox liquid oxygen breathing apparatus

Date: 17 April 2003


JW. Bech


Siebe Gorman & Co Ltd

Chessington, Surrey




Land of origin



Special Note: 

Liquid oxygen unit


User group

Mine rescue / Firefighters


Part no:



Working principle

CC SCBA by means of liquid oxygen evaporation


Gas type

Pure oxygen


Cylinder volume

5,5 lb // 2,5 kg


Oxygen flow

6-12 ltr/min


Max. cylinder pressure

No cylinder


Material of cylinder



Counterlung inspire

5 litres


Counterlung exhale



Operational use

120 minutes


Safety factor


30 minutes

Magnetic signature



Weight ready to use in Air

13,4 kg


Weight ready to use in water

Not for UW use





Working principle of scrubber

Radial flow


Scrubber material

Protosorb or soda lime

6-10 mesh

Quantity of scrubber material

1,6 kg









On the back



Dual hose no shut off valve










Overpressure valve opens @ 

2.0 mbar overpressure

Dimensions l x w x h

495 x 381 x 159 mm

Oxygen is transported in Dewar Flask*



* Dewar Flask
A double-walled vessel with a vacuum between the walls to reduce the transfer of heat. Used for the storage of liquid gases and for other laboratory applications. Named after the British physicist, James Dewar (1842-1923).
More information:





Main properties of liquid oxygen:

Oxygen liquefies at -184 gr.C, and is bluish in colour. This gas in its liquid form is strongly magnetic. Density 1.43


If you have any information to add this sheet please mail it to References to source and names will always be added!  

Info found:



Description of the breathing and oxygen addition system:

  • The exhaled warm saturated air passes from the mouthpiece through the exhalation valve housed in it, along the exhale breathing tube into the purifying canister.
  • When the air in the cicuit reaches a pressure of 0.8 in (2,0 mbar) water gauge, any further exhaled air is discharged to atmosphere via the automatic relief valve.
  • The exhaled air passes through the radial flow purifying canister where carbon dioxide is absorbed.
  • The purified air passes over one end of the liquid oxygen pack into the breathing bag.
  • This cools the air and condenses the moisture which collects in the breathing bag.
  • The heat from the purified air surrounding the liquid oxygen pack stimulates the evaporation of oxygen. The oxygen gas passes from the innermost container to and fro through the outer cases, and, by so doing, slows down heat input to liquid oxygen. As the cool gaseous oxygen flows out of the evaporating tube, it mixes with the purified air in the breathing bag, further reducing the air temperature and condensing more of the moisture. The condensate falls into the breathing bag where is remains trapped.
  • Oxygen enriched air from the breathing back passes over the liquid oxygen pack between baffles to increase its path, and, in the process, is further cooled.
  • The now cool, fresh, dry air passes along the inhale breathing tube and through the inspiratory valve into the mouthpiece.


Description of the evaporator on the Aerorlox apparatus:

This consists of a perforated tinned brass inner case packed with calcined asbestos wool. This case is surrounded by four further tinned brass cases, the inner three of these taking the flow of evaporated oxygen from the centre case through suitably placed apertures into the fourth section, through which regenerated air from the purifier also flows. A plug screws into a filling orifice on the outside of the evaporator and this orifice connects with the inner canister containing the calcined asbestos wool. The calcined asbestos wool serves to soak up the liquid oxygen charge thus preventing the liquid from swilling about inside the evaporator.


What advantages does the Aerorlox possess over compressed oxygen types of self contained breathing apparatus?

  • Cooler to wear
  • Less resistance to breathing
  • Dryer inspired air
  • Carried completely on the back
  • Lighter in weight
  • Full automatic use
  • No high pressure parts
  • Gets lighter in weight as it is used
  • Plentiful supply
    of oxygen

What disadvantages does the Aerorlox possess over compressed oxygen types of self contained breathing apparatus?

  • Extra equipment to carry to Fresh Air Base
  • Not immediately ready for use
  • Intermittent use not possible
  • No pressure gauge and thus no indication of time worn
  • Entrapped procedure is not possible
  • Air sampling may not be truly representative due to automatic relief valve blowing off.


A special thanks to the Grampian Speleological group for providing me with this information.
and special thanks to A.L. Jeffreys who provided the Aerorlox manual ans maintenance instructions!
There great site is to be found here:


Mr Wilf Robinson (died in 2013), father of Brian Robinson, filling an oxygen flask



I have not seen  mention of the Aerorlox Mk2, I use to work at Siebe Gorman and worked on this unit plus also admiralty stuff. It was an upgrade to 6 Hours duration.

Hi Jan

 Unfortunately I don't have much info on the unit, what I can tell you is that there was no difference externally as we used the same case. The major changes were inside, from what I can remember (some 30 years ago) was it had a larger cylinder and from this came a long thin coil, it was about 50+ turns and approx 100mm diameter, this was a new approach to stop liquid oxygen getting though to the user and to save space the cylinder went through the middle of the coil enabling the use of a larger one, so the time span was increased from 2 to 6 hours.

 I'm afraid this is all I can remember.

I can tell you a little story regarding this unit and the USA.

This unit was for deep mine rescue for the the likes of Canada, South Africa, Australia etc, now the US BofM (which used to be the abbreviation for the US Board of Mines) would not let this unit be used in the USA as there was no audible warning as to when the cylinder was running out.

There was a major disaster in one of the mines in the USA (it was in the 70's, can't remember where) now the problem was well deep and it was going to take approx 2 hours to get to the incident !!!.This Mk2 was the only unit that could do it, the owner of the mine went against the US BofM and contacted a mine in Canada asking if they could lend them some units, they could only let them have a few as they obviously needed to keep some incase they had a problem and suggested they contact Siebe Gorman to see if they could help. Now at the time I was working in the tool room and we had our managing director come into the tool room with staff of the light assembly department and explained the situation to us.

We could help, as we had 40+units assembled and ready to go out, the problem was that we had no bottles for these units, USA had plenty, but as usual  the USA they had different bottle theads so we had a mad session doing mods.So, light assembly were stripping the units down, the bottle valve was brought to me in the tool room, I was remachining the threads to suit the USA bottles, from me the valves were taken to the plating shop and then a full circle back to the light assemble to rebuild and test.

It was quite late at night when we finished, the police were waiting outside to escort the units to Heathrow (I think) and off they went.

I can't remember the outcome with the mine. After this the US Bof M allowed the unit to be used.


Just in passing, do you know what the 2 metal strip that run from top to bottom on the lid are for? They are not there to give strength to the case, they are skids, so rescuers don't have to crawl through small gaps, they could lie on their backs and slide along using the feet to push them along.

Best regards 


Update aug 2014;

There is a part about Aerorlox Mk2. The information is slightly incorrect

First, the Mk2 was to 3 hours not 6, simply by retesting to that time, it worked. 

Of course it mentions "cylinder", the Aerorlox had liquid oxygen not a cylinder, so no thread changes,,,,. The mine he mentioned in the US was Sunshine Silver mine in 1972 where 100 men died. There are photos of teams using the Aerorlox there

Thanks Brian!


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