Working at High Altitude

This issue of High Altitude Medicine & Biology includes a Pro/Con feature on “Hypoxic Cardiopulmonary Exercise Testing Identifies Subjects at Risk for Severe High Altitude Illnesses.” This topic is particularly interesting in the context of selecting workers who can perform well at high altitude. The problems of lowlanders working at high altitude have not received a great deal of attention but it is an increasingly important topic of research. This prompts us to look at three relatively recent challenges: The development of new mines at very high altitudes, the Chinese train to Lhasa that goes through an altitude of over 5000 m, and new telescopes that are being sited at altitudes of up to 5600 m.

One of the most interesting recent challenges is a new mine in Peru called Toromocho. This is close to the old town of Morococha, altitude 4550 m, which itself is the site of a very old copper mine. In addition a silver mine is located nearby. The town of Morococha is situated on a very large copper deposit that, because of improvements in methods of extraction, now means that this is one of the largest accessible deposits in the world. However because the ore is located under the existing village of Morococha, it has been necessary to relocate this a few miles to Toromocho. The mine owners have built a new town with many conveniences such as adequate clean water and modern toilets, and the residents of Morococha are given a financial inducement to move to Toromocho. Naturally there is some reluctance on behalf of some residents who have been there for many years or even generations.

The ore in Toromocho is located at altitudes up to 4900 m. Working at this altitude is a substantial challenge especially as mining operations these days require the operation of very sophisticated equipment including enormous mechanical shovels, loaders, and trucks. Although Morococha has an indigenous population who are used to working at high altitudes, this heavy and expensive machinery requires operators with a degree of training that few of these people have. Therefore most of the workers will necessarily come from low altitudes and the working conditions will be very severe for them.

Not only is the mining by day an enormous challenge but the living quarters will be very high, and this will mean substantial problems. It is not clear at the present time how these will be met. Many lowlanders who go to high altitudes find that their biggest problem is sleep. The new Toromocho mine is an example of how the increasing pressures to obtain commodities such as copper are forcing mines to go higher and higher.

The Chinese train from Golmud to Lhasa that passes through altitudes exceeding 5000 m has been discussed here before but remains a fascinating high altitude challenge. The train begins in Beijing near sea level and for most of its three days and two nights to Lhasa the altitudes are moderate. However the final day's journey from Golmud to Lhasa crosses the Kunlun Mountains at an altitude up to 5072 m. Passengers from Beijing have developed a minimal degree of acclimatization during the previous two days and so the hypoxic insult is substantial.

The ingenious solution has been to equip each passenger car with an oxygen generator that raises the oxygen concentration from the normal value of 21% to about 25%. Although this sounds like a small increase, it is actually very effective. It turns out that every 1% increase in oxygen concentration reduces the equivalent altitude by about 300 m. In other words a passenger traveling through 5000 m actual altitude who is breathing 25% oxygen will have the equivalent altitude reduced by 4×300=1200 m. This equivalent altitude of 3800 m is much less hazardous than 5000 m. Of course an additional advantage is that the passengers are essentially at rest during the whole trip and so the situation is very different from working in a mine. Nevertheless there have been some reports of illnesses in the train resulting from the altitude.

The third example of working at increasingly high altitudes follows the siting of new telescopes. Some of these are in north Chile on the Chajnantor Plateau east of San Pedro de Atacama. The biggest project, indeed the largest astronomical project in the world, is the radio telescope known as the Atacama Large Millimeter Array. This consists of 66 giant antennas in a moveable array at an altitude of 5000 m. While it is true that most of the observers will work at a lower altitude, and the data will be fed down to them through optical fibers, an enormous facility like this requires a certain number of people to be present for maintenance and repairs.

Here oxygen enrichment of room air is very valuable. This was first used in a smaller radio telescope called the Cosmic Background Imager owned by the California Institute of Technology. In this the operators worked in an atmosphere of 27% oxygen, which reduced the effective altitude from 5000 to 3200 m. It is a fact that people at an altitude of 5000 m have impaired cognitive function. They tend to make many errors and have reduced problem-solving abilities. Raising the inspired PO₂ is the only solution. This can either be done in a facility by enriching the room air, or if workers have to go outside to make repairs, they can use portable oxygen with nasal cannulas.

Astonishingly, telescopes are now being placed even higher. An advantage of these great altitudes is that the water vapor pressure is very low and this improves the function of the instruments. As of now the record seems to belong to the Tokyo Atacama Observatory at an altitude of 5640 m. At present this facility only has a small 1.0 m optical infrared telescope but eventually it will house a 6.5 m instrument.

The relentless demand for minerals such as copper, and the clear advantages of very high altitudes for some telescopes makes it inevitable that humans will continue to work at higher and higher altitudes. The resulting medial and physiological problems will become increasingly challenging.