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 levels below 3 ppm are stressful to most aquatic organisms. Levels below 2 ppm will not support fish at all. Low dissolved oxygen levels can be the result of elevated temperature and thus the inability of the water to hold the available oxygen.Low 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.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.