Hello, welcome to the forum. If a person has lung cancer, they would need to not live in the house while the floors are refinished. That's the usual recommendation. If they could move out during the process and stay somewhere else, that is best. What was the outcome of the situation? https://www.verywellhealth.com/wood-dust-and-lung-cancer-whos-at-risk-3971878 After the job is finished, it should be thoroughly cleaned. So, they do need to take precautions and that you are a good citizen and ethical to be aware of this for them.