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.
One unit of measure of dissolved oxygen in water is parts per million (ppm), which is the number of oxygen (O2) molecules per million total molecules in a sample.ow dissolved oxygen levels can also indicate an excessive demand on the oxygen in the system. Some pollutants such as acid mine drainage produce direct chemical demands on oxygen in the water for certain oxidation-reduction reactions.