Lack of attention to observance of safety tips on working inside manholes causes unfortunate incidents. While incidents could be prevented by having the appropriate equipment and being cautious. For instance, in two similar incidents in Azar and Dey of 1396 in Isfahan, 8 workers in total who were resolving congestion in the sewer network, due to lack of attention to these tips and not having the appropriate equipment, got involved in incidents, in which unfortunately 5 lost their lives.
Such incidents make the necessity of observance of safety tips and attention to hazards related to manholes more manifest.
Manhole related hazards:
Hazards Caused by The Surrounding Environment (Car Traffics & etc)
Falling into The Manhole
In order for the worker to go inside the manhole, the following methods can be employed:
Using a Ladder
Using a Safety Harness and Rope with Safety Tripod or Crane
Also, to prevent the fall of pedestrians into an open manhole, the following methods can be employed:
Using a Secondary Reticulated Cover
Applying Portable Guardrail on the Entrance of the Manhole
Placing Danger Signs Around the Manhole
Using a Secondary Reticulated Cover on the Manhole
Using a Safety Tripod with Special Strap for Entering Manholes
Atmospheric hazards include the following attentions:
Lack of Oxygen Inside the Manhole
Accumulation of Toxic Gases Inside the Manhole
Accumulation of Flammable Gases Inside the Manhole
Since the sewer network is the place of flammable and toxic gases accumulation, it’s necessary to put a hole in the manhole cover before entering. so that the gas density inside the manhole is examined by an electro-gas machine and if needed, the worker go inside the manhole with an oxygen tank.
The Hole Put on the Manhole for Checking the Gas Density Inside the Manhole
Hazards Caused by Lifting the Manhole Cover
In case of lifting the manhole cover by hand, the following hazards threaten the worker:
The Cover Falling on the Leg – Having Fingers Stuck Under the Cover
High Pressure Applied to Back Due to the Heaviness of the Cover
For such purpose, using special equipment for lifting the cover is essential.
Lifting the Manhole Cover by Appropriate Equipment
Drowning Inside the Manhole
To resolve the congestion of the sewer network, the worker should have access to the sewer pipe through the manhole.
Hazards caused by the flooding of the water accumulated behind the place of sewer blockage may cause the worker to drown inside the manhole.
For this purpose, cylindrical pipe plugs can be used on the upper side of the place of blockage.
An Example of a Cylindrical Pipe Plug
Hazards Caused by The Surrounding Environment (Traffic)
In case of working inside manholes installed in the course of traffic, the following tips should be considered:
Closing the Area Around the Manhole by Traffic Signs
The Working Schedule not Interfering with the Peak Hours
If Needed, Placing Heavy Vehicles Dangerous Signs Around the Manhole
Manhole Falling Risk Sign