The standard sets a permissible exposure limit (PEL) of 25 parts methylene chloride per million parts of air (ppm) as an eight-hour time-weighted average (TWA). This refers to the average exposure during an eight-hour period. Employers must use engineering and work practice controls to limit employee exposures.
The state of the atmosphere at a particular time and place. Weather is described in terms of variable conditions such as temperature, humidity, wind velocity, precipitation, and barometric pressure. Weather on Earth occurs primarily in the troposphere, or lower atmosphere, and is driven by energy from the Sun and the rotation of the Earth. The average weather conditions of a region over time are used to define a region's climate.
Weather is the state of the atmosphere at any given time and place, determined by such factors as temperature, precipitation, cloud cover, humidity, air pressure, and wind. The study of weather is known as meteorology. No exact date can be given for the beginnings of this science since humans have studied weather conditions for thousands of years. Weather conditions can be regarded as a result of the interaction of four basic physical elements: the Sun, Earth's atmosphere, Earth itself, and natural land-forms on Earth.