Are you assuming most Bitcoin mining is on Chinese coal electricity? Other forms of electricity are 5-10x safer.
Luckily trends show that this will happen soon, but other challenges posed in Africa is political stability (e.g. government decides BitCoin mining is illegal or imposes unreasonable taxes due to lack of understanding), lack of competency, and other types of infrastructure.
The only countries I can see that are suitable are South Africa and Namibia.