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).
OSHA sets limits for the amount of chemicals workers can be exposed to during their work shift. OSHA has the power to enforce these limits. The Permissible Exposure Limit for ammonia set by OSHA is 50 parts per million (ppm) averaged over an eight hour work day. This is the standard that must be met in every work place. For example, this means you can be exposed to 100 ppm for 4 hours of your shift as long as you are not exposed to any ammonia for the other 4 hours of your work day.