Malaria and Yellow Fever killed most workers.
I will take a guess but it is not a wild one. I believe the answer is disease and more specifically, malaria.
There were normal dangers of construction. They had heavy machinery moving about, the danger of large mud and dirt slides caving in on them. One big difficulty was malaria. Many workers died of yellow fever.
Malaria, yellow fever
malaria and yellow fever
Malaria and Yellow Fever.
Yellow fever & malaria.
false
Malaria and Yellow Fever.
Malaria Dengue Filariasis Yellow Fever Chikungunya
Malaria denge fever or yellow fever rabies depends on the animal
If you mean long ago, they didn't have antibiotics or vaccines so they had to treat the symptoms. This means to give something to bring down the fever, etc. Both malaria and yellow fever are carried by mosquitoes. That meant protecting people from them by draining standing water and using mosquito nets. Now there are vaccines for yellow fever and malaria.