Can my boss make me work all day and night without any sleep?

The company I work for is an industrial consultant. We inspect pipeline welds using non-destructive methods to insure their integrity. It is a VERY physically demanding job. Recently, I have been working 7 days a week, which isn't too much fun but isn't the real problem I have. My boss has recently decided to send my brother (who I work with) and myself to do another job at night after our first job is over. Consequently, in the course of 3 days we got 4 hours of sleep. We don't work every night, but we do this a lot during the week. Not having enough sleep in this profession can be very dangerous as we work with radioactive material. If we're too tired, we might start cutting corners resulting in serious injury or possibly death. My boss doesn't seem to think this is a problem as he receives a share of the profits at the end of the year so he is monetarily motivated to make others do the work. I live in Kansas and I don't think there's a labor law against this. What should I do?