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.
It is essential for the survival of fish and other aquatic organisms. Oxygen dissolves in surface water due to the aerating action of winds. Oxygen is also introduced into the water as a byproduct of aquatic plant photosynthesis. When dissolved oxygen becomes too low, fish and other aquatic organisms cannot survive.The DO test tells how much oxygen is dissolved in the water.However, it does not tell you how much oxygen the water is capable of dissolving at the temperature at which it was measured. When water dissolves all of the oxygen it is capable of holding at a given temperature it is said to be 100% saturated.xygen is also introduced into the water as a byproduct of aquatic plant photosynthesis. When dissolved oxygen becomes too low, fish and other aquatic organisms cannot survive. The DO test tells how much oxygen is dissolved in the water.