Many people are still being exposed to secondhand smoke while at work.
Cdc researchers studied data from a 2015 national health survey And nearly 20-percent of nonsmoking employees were exposed to secondhand smoke at the workplace.
Ten-percent said they were exposed at least twice a week.
Those working in industries that have outdoor workplaces such as construction had the highest rate of exposure.
Employees who lived in states with comprehensive smoke-free laws were least likely to report exposure.
Previous studies have shown that exposure to secondhand smoke could increase the risk for developing heart disease, lung cancer and stroke.
The data came from the 2015 National Health Interview survey occupational health supplement.