Can boss make you work in unsafe place?

Today at work a lot of the workers were complaining about headaches,burning eyes and sore throats. There was a foul oder that no one could say what it was. Some thought it was a gas oder. The one boss said he could smell it but the big boss said he could not smell anything. After about a half hour (workers were out side most of the time)most of the workers refused to return to work until the gas company was called. The boss said no because he didn't think it was gas. He order everyone back to work, but most wanted to go home because of head aches and such plus they felt unsafe working. So the big boss said if we leave we would be written up as unexcused. All left but about 5 people.
Can he (boss) do this?? ED in PA.

Contact OSHA.