Because the canal under the manhole cover is a sealed site, the concentration of methane, carbon dioxide and other gases is often too high. Cleaning workers, canal repairers, telephone line technicians, firefighters and other personnel need to use ventilators to introduce fresh air on the ground before entering the work to avoid hypoxia or gas explosion, resulting in occupational disasters.
Extended data;
The reason why CMC is round
1. The manhole is located on the main road, and people come and go every day. Attention should be paid to the safety of pedestrians when designing, and the manhole cover should not fall into the manhole. If the design is triangular or square, although the cover is larger than the parallel opening, it may still fall off. And if it is round, because the diameter of the circle is equal, the cover will not fall off as long as it is slightly larger.
2. Due to sound reasons, it is sometimes necessary to comb or thread manually. At this time, the larger the area of Baojing, the better. In these figures, when the perimeters are equal, the area of the circle is the largest. At the same time, the circle conforms to our body shape, which is convenient for staff to go in and out.
3. The sides of a triangle or a square are composed of straight lines with sharp corners? If it is encountered during maintenance, it is easy to get hurt. ? And the edge of the circle is an arc, so this problem will not appear.