This will depend largely on the individual. A man who is not in good shape may be able to lift a load that is heavy for him, and do it unsafely. A man who is stronger and well-trained, would not be bothered by the same load and be able to safely lift it and much more.
The dangers of heavy loads include control of the load, physical limitations of the person, and health effects. Losing control of a weight can lead to injury by losing balance, dropping the weight, or using poor body mechanics. Physical limitations could include grip strength, whether the person has a strong enough core, or any old injuries that could recur. And, then there are health effects. A person may suffer hernias, burst blood vessels, particularly aneurysms, torn muscles, torn ligaments, and even fractured bones. They may have the muscle to life the weight, but the rest of the body may not be able to handle the strain.
The world record weight is a bit over 1000 lbs, which very few people in the world are capable of attempting safely or unsafely.