CDC names the main problem at altitude as hypoxia, caused by the fall in the partial pressure of oxygen. The operator's own pages state that the standard routes need no ropes, crampons or ice axes.

How high it actually is

The park authority states that the park holds Kibo at 5,895 m, Mawenzi at 5,149 m and Shira at 3,962 m. The route hub lists four summit base camps, from Barafu Camp at 4,670 m to Kosovo Camp at 4,870 m, and the operator's own pages give Barafu four different altitudes.

Fitness does not reduce the altitude risk

CDC is blunt: "Training and physical fitness do not affect risk." It states that any unacclimatised traveller going to a sleeping altitude of 2,450 m or more, and sometimes lower, is at risk of altitude illness. The NHS puts the threshold at usually more than 2,500 m, names Mount Kilimanjaro as one of the places it happens, and says you are more likely to get it if you ascend quickly. CDC adds that at around 3,050 m the inspired oxygen pressure is only 69% of the sea-level value, and that the body can adjust to moderate hypoxia at altitudes of roughly 5,200 m or less but requires time to do it, with the acute part of that process occurring over the first 3 to 5 days after ascent.

The three illnesses, by name

CDC divides altitude illness into AMS, high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE). For AMS, headache is the cardinal symptom, usually with loss of appetite, dizziness, fatigue or nausea, and onset is usually 2 to 12 hours after arriving high. HACE is described as end-stage AMS, presenting with altered mental status, ataxia, confusion and drowsiness, and CDC states that "Coma can ensue within 24 hours of onset". The UIAA notes that with HACE "there is loss of insight, by the patient, who may insist that they are all right", and offers the heel-to-toe walking test as a field check. Of HAPE, CDC states "Early diagnosis is key; HAPE can be more rapidly fatal than HACE".

The ascent rules the authorities publish

CDC, reporting the Wilderness Medical Society, says that once above 3,000 m you move sleeping altitude by no more than 500 m per day and add an extra acclimatisation day for every further 1,000 m of sleeping-altitude gain. The UIAA sets 300 to 500 m per night above 2,500 to 3,000 m, and two nights at the same altitude after every 2 to 4 days of ascent. The NHS says a rest day at the same altitude every 3 to 4 days above 3,000 m, so the three sets of numbers differ and each is given here as its own authority states it. The UIAA aims one line squarely at the booking decision: "prevention starts before booking! Check carefully the profile of your tour!" The park authority states the relationship in words: "The more days, the higher the possibility to conquer the summit." The operator recommends 7 to 9 days for almost every climber.

Going down is the treatment

CDC states that AMS improves rapidly with a descent of 300 m or more, and that if symptoms worsen at the same altitude despite treatment, descent is mandatory. For HAPE it states that descent is urgent and mandatory, and that descent and oxygen work better than medication. The NHS says go 300 to 1,000 metres lower; the UIAA says descend at least about 500 m, to the last camp where you were well. The rule underneath all of it is CDC's: "Never ascend to sleep at a higher altitude when experiencing symptoms of altitude illness, no matter how minor the symptoms seem."

What the days demand, and who calls it

The operator gives the daily load as 5 to 8 hours of moderate-grade hiking for 6 to 10 days with a 6 to 8 kg daypack, and summit day as 14 to 16 hours of total movement. Its training page is straight about the limit: "Altitude tolerance: This you can't train at sea level." Its safety page describes health assessments of every client every two hours, with pulse oximetry and stethoscope evaluation of lung sounds, and states that "the guide's decision is final and supersedes any summit ambition". Ask any company you are considering what its guides assess every two hours, who records it, and who has the authority to turn a client around.

Where to go next

For the six-hour benchmark hike, read the operator's own fitness guide: https://gokilimanjarotreks.com/blog/how-fit-do-you-need-to-be

Sources