Heritage

Oxygen deficit is every pilot’s worry

kq pilot

A Kenya Airways pilot at Jomo Kenyatta International Airport, Nairobi. While there are many systems designed to warn pilots of decompressions, they are still trained to recognise a lack of oxygen. Photo/FILE

As we go about our activities on earth we are immersed in an ocean of air that exerts pressure equal to about a column of mercury 760 millimetres high at sea level. As you go up this pressure decreases.

A variety of gas laws formulated by chemists in the 19th century inform us that the number of gas molecules per unit volume of air decrease as well. So much so that at Nairobi, 5,000 feet above sea level, the amount of oxygen in 17 per cent less than it would be at sea level.

The body generates most of it’s energy through an oxygen dependent processes. Consequently, when the amount of oxygen reduces the body cannot operate efficiently. The nervous system is especially sensitive to oxygen deprivation.

Most of the world lives in low-lying areas and when people travel to higher regions they encounter some challenges. South American countries have complained for years of having to play World Cup qualifying matches in Quito, Ecuador, at 9,000 feet.

The thin air saps the visitors of their energy and has resulted in the home team scoring some famous victories against much fancied opponents.

Mountain climbers are advised to ascend no more than 1,500 feet per day. This allows their bodies to acclimatise and get better at using the lower oxygen concentrations.

Past a certain altitude though, the amount of oxygen is not enough to sustain life, forcing people to use supplementary oxygen. Airliners fly at altitudes of up to 40,000 feet, higher than Mt Everest. For flying to be accessible to the general public, planes are pressurised. This is normally set to make the cabin equivalent to breathing air at about 6,000 to 8,000 feet.

Warn pilots

On occasion though, the pressurisation system fails. Explosive decompressions, while dangerous, have the advantage of being easily detectable by the crew. Much more insidious are slow decompressions.

While there are many systems designed to warn pilots of when this happens, we are still trained to recognise a lack of oxygen also known as hypoxia. The symptoms of hypoxia are many and varied.

They include delayed reaction time, poor judgement and loss of muscle coordination. It is also worth noting that they closely resemble the symptoms of being drunk.

In this state, flight crew might be unable to carry out functions necessary to save themselves. For this reason, emphasis is on recognition of symptoms before the crew run out of time.

Should the cabin altitude go above 14,000 feet, oxygen masks are set to deploy automatically. While the oxygen lasts for only 15 minutes, it is usually more than enough for the crew to descend to a lower altitude where there is more breathable air.

Dr Ondieki is a pilot with an international airline