The expansion of oil and gas drilling in the United States has turned the world's energy economy upside down. For the first time in 20 years, the country is producing more oil than it imports. The rapid increase in production, driven by hydraulic fracturing or "fracking," has also started a passionate argument about safety and environmental protection. But the drilling industry's status as one of the most dangerous in the country for workers is often overlooked. It's rarely mentioned, even though many of the threats to workers, such as explosions and toxic gases, also present a threat to the general public.