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).
For airborne exposures, there are three types of limits in common use: 1  the time-weighted average (TWA) exposure limit-the maximum average concentration of a chemical in air for a normal 8-hour working day and 40-hour week;he legal basis for the preparation of occupational exposure limits and biological limits in the European Union is contained in Directive 98/24/EC on chemical agents and Directive 2004/37/EC on carcinogens and mutagens.