The automatic cab signal system shall be arranged so that cab signals will be continuously controlled in accordance with conditions described in Â§ 236.205 that obtain at least stopping distance in advance. Â§ 236.512 Cab signal indication when locomotive enters block where restrictive conditions obtain.
Dissolved oxygen (DO) is a measure of the quantity of free oxygen molecules in water. The concentration of DO is an important indicator of the health of an aquatic ecosystem because oxygen is essential for almost all forms of life. Oxygen is necessary for respiration and for some chemical reactions.
Dissolved oxygen is measured in milligrams per liter (mg/L). One milligram (mg) is 1/1000 (one thousandth) of a gram or 1/1000000 (one millionth) of a kilogram. 1 kilogram of water weighs 1 kilogram and occupies a volume of 1 liter (L).Therefore, expressing dissolved oxygen in mg/L is the same as using units of parts per million (ppm).Twelve parts per million (12 mg/L) is the highest amount of oxygen that can be dissolved in water under standard barometric pressures (sea level); 12 mg/L is known as the saturation point.Zero parts per million (0 mg/L) is the lowest amount of dissolved oxygen in water.ince, the amount of oxygen dissolved in water is small compared to the weight of water, it isn't appropriate to describe the level of dissolved oxygen in terms of a percentage.