Ships of the desert. Camels were domesticated more than 3,000 years ago, and to this day, humans depend on them for transport across arid environments. They can easily carry an extra 200 pounds (90 kilograms) while walking 20 miles (32 kilometers) a day in the harsh desert.
Definition - What does Permissible Exposure Limit (PEL) mean? Permissible exposure limit (PEL) is the legal limit in the U.S. for maximum concentration of any chemical in the air to which a worker may be exposed continuously for eight hours without any danger to health and safety. PEL is established by the Occupational Safety and Health Administration (OSHA).
In the same way, 105 CMR 120.200 establishes a limit for normal occupational exposure of 5 rems (0.05 Sv) a year. Although you will not necessarily get cancer or some other radiation effect at doses above the limit, it does mean that the licensee's safety program has failed in some way.