Re: How Fast does an average Human Being exhale?

Hi Rachel!

This is one of those questions that looks easy and then turns out to be much more difficult to answer than you first imagine - so thanks for asking a REALLY difficult question!

The problem starts with the definition of 'average human being'! Not only do we all have different sized nostrils, but we also breathe at different rates at different times - slowly and shallowly when asleep, for instance, but fast and deep when trying to catch the bus! We also change our breathing pattern during our lives, with babies and yound children breathing faster than adults.

My research ALSO found that EACH BREATH is also different - it starts slowly, reaches a peak and then falls away as we get to the end of wach breathing cycle.

So...... How fast does the average human being exhale'? Each lung has a tree-like network of branched tubes inside it - beginning with the single wide traches, through the main branches of the bronchi (1 for each lung) and then down through the many bronchioles, before ending in the 6 million of so tiny air sacs (or alveoli) in each lung. It is when the bronchi get inflamed that we get a bad cough - called BRONCHITIS - and when the alveoli get damaged that we slowly become short of breath - EMPHYSEMIA - whilst someone with ASTHMA has a narrowed trachea during an attack.

A reasonable average for the volume of air we breathe when resting would be 1.8 litres/min - or about 3 pints/min. This translates into a speed that varies from the wide diameter of the single trachea, through the 2 bronchi down to the many bronchioles inside each lung. The speeds seem to be:
Trachea : 8.8 miles/hour or 3.93 m/s (about 13 ft/sec)
Bronchi : 11.1 miles/hour or 4.97 m/s (about 17 ft/sec)
Bronchioles (large) : 0.56 miles/hour or 25 cm/s (about 10 inches/sec)
Bronchioles (small) : 0.022 miles/hour or 1.0 cm/s (about 0.5 inches/sec)
Alveoli : 0.0022 miles/hour or 0.1 cm/s or about 1/25th inch/sec

That took me a LOT of researching - so it seems that your Snapple cap was not far out (the figures I have given were just what ONE researcher found!).
Thanks again for asking one of the most tricky questions I have had! Keep on breathing well - life is SO much better with it! :)
Ian