Inspecting the inside of a manhole may not be something that you have to do every day, but a situation may occasionally arise where you would need to do so. With this in mind we thought that it would be good idea to go over some of the key points that must be adhered to in order to carry out an inspection safely.
Before entering the confined space of a manhole one should carry out some atmospheric tests in order to establish the conditions below ground.
There are three main tests to complete, these are:
• Oxygen content – A safe working oxygen level is between 19.5% and 21% and one should only enter into a confined space if the level underground is reading between these two figures. Constant monitoring of the oxygen levels is vital as suffocation in confined spaces is a very real threat if the level should drop. Conversely, should the oxygen level rise, there is a risk of explosion or the accelerated burning of flammable materials.
• Flammable or explosive gas check – The confined space should be checked for these gasses as the tiniest amount could cause an explosion should it come into contact with a spark or a flame.
• Toxicity – The toxicity level should be monitored in order to assess whether it is safe to enter the manhole or not. Any concentration of vapours can cause harm to the person entering the confined space.
All of the atmospheric tests must be carried out at all three levels of the manhole (top, middle and bottom) and for a minimum of 60 seconds each. With the help of manhole lifters, open the access point slightly and lower the detector or aspirator pump into the shaft to the desired level.
Ventilation systems should be in place and in operation both before and during any confined space inspection. A fresh air blower will help keep the flow of fresh air moving through the area, essential whenever diesel-fuelled machinery or gas cylinders are in operation.
Never, under any circumstances, use petrol-fuelled engines underground as the carbon monoxide from the exhaust is extremely dangerous.
Manhole cover lifting
The removal of the cover to the access point of the confined space should only be attempted with the correct manhole lifters for that particular cover.
Using the wrong type of hook or pick can result in injury and should be avoided. Before any manhole cover lifting takes place the assigned employee should have received adequate manual handling training.
General confined space good practices
Once the manhole has been tested and the cover has been removed you are now free to inspect the space as required. However, there is still great risk in entering a confined space so the following good practises should be closely adhered to at all times:
1. Ensure that the opening to the manhole is properly protected by erecting a temporary barrier around the entrance to prevent accidental falling by fellow workers or passers-by. This will also lower the risk of objects being dropped down the manhole onto the workers below.
2. Have a minimum of two people present at all times whilst working on a manhole. One should be the observer who can assess any potential hazards from ground level while the other works underground. Never enter an unattended manhole.
3. Never smoke, produce sparks or light open flames in or around an open manhole.
4. Wear protective clothing including non-sparking, non-slip footwear.
5. Be aware of the structural soundness of the steps/ladder inside the manhole. For vertical descents a safety harness should be used unless there is a threat of entanglement.
6. Lower tools down with a rope prior to entering the space. Do not carry tools or equipment down by hand. The same applies for removing them from the manhole.
7. If portable lighting is required use only explosion proof rigs and ensure that all tools are non-sparking.
8. Be aware of the emergency procedure for each particular confined space. Know your contingency plans and emergency arrangements before entering.
9. Follow the Confined Spaces Regulations Act 1997 and check to see if any other legislation applies to the task at hand.