Cabin Air Refreshment Rates

[Milt]

Can anyone advise what the current requirements are for the rate of replacement of Cabin Air and how much recirculation is a maximum for a civil airliner?

[Romeo Hotel]

Believe it's a 1lb of air per seat per minute. Roughly 50% is recirculated after going through HEPA filters

[munster]

It used to be 1lb of air per passenger per minute. Who knows what the Europeans did to the figures though!

[ICT_SLB]

This link takes you to a Boeing article. Note that it uses the 767 as its baseline and gives all amounts in cu ft/min. It does however cite multiple sources as well.
http://www.donaldson.com/en/aircraft/cabinairquality/supportDocs/18%20Issues%20Pertaining%20to%20Flight%20Attendant%20Comfort .pdf

[Milt]

Thanks ICT_SLB for the link. A most interesting coverage of the modern airliner's cabin air circulation and recirculation. We TPs rarely get involved in that stuff although I am now left wondering and wanting to know the extent of the thrust which must be lost for a typical engine installation with all of that air being bled from the engine compressor. The article mentions that occasionally pilots may shut down the air bleeds during take off for operational reasons.

During the tests on the Comet 2c before it went into RAF service I was tasked to run one on the ground for an hour or so whilst the boffins over pressurised the cabin to 23.7 psi or +9 on 14.7. They had strain gauges on selected areas of the fuselage.

I expected some physiological effects but didn't detect anything unusual.

[John Farley]

Milt

It is not surpriising that + 9 psi over atmos did not produce symptoms.

When at 33ft scuba diving you are at 2 atmos - and that is no depth of course.

Amateur scuba divers suitably trained by PADI (like the good duchess recently) are cleared to 100ft or 4 atmos total.

[ICT_SLB]

Milt,
When he produced the first dive tables for the Royal Navy around WW1, Haldane found that there will be no bubble formation (the source of the "Bends") if the differential pressure ratio is less than two i.e. you can stay down at 2 ATM (32 feet) indefinitely without any effect. However if you had had an explosive decompression the sudden delta P could have given you problems.

John,
Did your Duchess qualify outside of the UK? When I left in 1980, the British Sub-Aqua Club was the main SCUBA training agency not "Put Another Dollar In".

[John Farley]

ICT_SLB

According to the press she did it in the Caribbean.

I did a PADI OW course in Malta in the 70s and then it was 2 weeks of very hard work, both therory and practical including a final night dive test.

Things may have changed since then though.