There are 3 lakes in Africa (Monoun and Nyos in Cameroon, and Kivu in the limit of Rwanda and Congo) that concentrate in its depth large quantities of CO2 and Methane. These gases, highly mortal and harmful for our skin, are emitted due to volcanic activity, earthquakes or detachments of land. The gas comes from the lake and moving up to 2 meters of height from the level of the soil it can manage to cover approximately 30 kilometers to the semibreve of the affected lake.
The presence of this gas can extend for near 24 hours. The last disaster of this type happened in 1986 had near 2000 mortal victims. The great danger is more than 2 million persons live in the surroundings of these 3 lakes. When one of these events happens (and since the gases are invisible) alarms that alert the population are activated, but its exodus becomes impossible by the great existing volume of people and animals, and for the lack of effective means of transport.
In these areas life depends of the coexistence of man and animal. The solution consists of a refuge of double skin (leather), capable of sheltering an average family and its cattle separately (in average 5 heads of cattle or 15 heads of sheep). This refuge is totally hermetic in a height of 5 meters and has in its higher part a mouth that allows the entrance of pure and breathable air.