This article has been written out of personal and institutional experiences and should not be taken as a formal guideline for working in confined spaces. Please refer to relevant safety manuals before undertaking such work.
This is the second part of this series. Part 1 is an introduction to “Confined Spaces”.
Testing the Atmosphere
Never trust your senses to determine the presence or absence of gases in a confined space. Some of the toxic gases and vapours are colourless and odourless, hence you can neither see or smell them. You cannot determine the level of Oxygen present also by your nose.
The prevalent atmosphere should be tested using properly calibrated instruments / miner’s safety lamp etc before “Safe to work Certificates” are issued.
- Some of the gases or vapours are heavier than air and tend to settle to the bottom of a confined space – Example, Hydrogen Sulphide or Steam which do not sustain life.
- Some for the gases are lighter than air and will rise to the top of a confined space – Example, Methane, which does not sustain life.
- Some of the gases may have the same density as air and will occupy the rest of the space – Example, Carbon Monoxide which does not sustain life.
It is essential that all the areas in a confined space are tested for presence of gases and absence of Oxygen. In both the cases, the area is to be ventilated using external air sources (Supply or Exhaust or Supply and Exhaust). The exhaust gases should be let out to well ventilated spaces, preferably open air.
If steam or inert gases have been injected into a confined space, the space needs to be ventilated before effecting personnel entry since both steam and inert gases are non-life sustaining. For example, some of the aviation turbine fuel tanks are automatically filled with Nitrogen as the fuel level falls.
Steam will increase the temperature of the space and the space is to be allowed to cool before allowing people to enter and work.
Care should be taken so that no electrical spark is introduced into the confined space. The motor drive for the supply / exhaust fans and their controls should be outside the confined space.
After ventilating for about 24 hours, the confined space is to be re-tested for presence of hazardous gases and presence of life-sustaining levels of Oxygen. Personnel should be allowed to enter the compartment only when the test results are satisfactory.
Even after the atmospheric tests conducted in a confined space is deemed satisfactory, the condition can reverse due to the nature of work carried out within the space.
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For example, if a metallic tank is chipped and cleaned initially and paint application has been done, the paint fumes are both hazardous and flammable.
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Another example is hot work such as cutting / brazing inside a confined space will reduce the Oxygen level and leave hazardous gases within.
In all cases, periodic monitoring is essential to ensure that confined spaces are safe to work within. This is applicable for carrying out hot work onto the confined space walls from outside as well. For example, if hot work is to be carried out on to the metal sides of a confined fuel tank, the tank needs to be inspected and cleared as “Safe to work” periodically.
Isolation of the Confined Spaces
The confined space where work is to be carried out internally and externally should be isolated from all energy sources through “Lock Out Tag Out “ processes as follows:
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All electric circuits should be switched off and the incoming switch locked.
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All other energy such as hydraulic and pneumatic air supplies should be bled till empty and the supply valves are to be shut and locked.
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All mechanical drives such as belt or chain drives should be disconnected and stowed away.
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All mechanical moving parts within a confined space should be secured safely.
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The entry manhole cover should be opened and secured safely in the open position to avoid accidental closing.
Other Hazards
Confined spaces could also have other hazards such as:
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Low ceiling height causing personnel to crouch and move inside. Chances of banging head onto appendages and the ceiling can exist.
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Low or nil visibility since the space is not lit well.
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Slippery surfaces due to stored chemicals and even water.
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defective or missing ladder rungs in the space
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Falling objects; this could be from people working at higher levels within the space or material being removed / being cut.
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High temperature within the space due to exposure of the external surface to hot sun or low ventilation in the surrounding compartments. Periodic rotation of staff working inside is essential to reduce fatigue and dehydration.
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Noise is another hazard. Sounds may get amplified beyond allowable limits, within the space.
Personal Protection Gear
Though the list is not exhaustive, the following are considered essential:
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Chemical suites in case of entering spaces containing hazardous chemicals
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Industrial safety helmet, preferably with a miner’s torch on it.
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Breathing apparatus (Self contained or with re-circulation depending on the space content and current state) when the Oxygen levels are low or hazardous gases are still present.
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Ear defenders / plugs
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Eye protection
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Non skid safety shoes with rubber soles and steel toe caps
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Work gloves
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Fall arrester or full body harnesses; to be used while entering and leaving the space and if working at a height within the compartment.
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Safety communication and rescue rope lines. If the person working within the space is visible to the support person outside, rope communication lines are not necessary and voice communication can be resorted to.
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Lead lamps from a low voltage DC source
As part of the Hazard assessment, confirm whether the person entering the space can enter through the available opening, wearing all the protective gear and can be evacuated also in the same state. If not possible, alternative strategies will have to be devised.
Support and Emergency Team
No one should be allowed to enter a confined space without at least one person standby, manning the communication rope line, outside the space. The emergency rescue team should be in a quick access position to attend in case of emergencies.
Each person entering the space should have a buddy outside monitoring his progress.
The rescue process should be planned in advance and practiced regularly. An unplanned rescue act could endanger other lives also.
The people entering confined spaces and the support team are to be fully briefed about the hazards, work needed to be done, work process flow, who-is-to-do-what, sequence of entry / exit, tools and other material to be carried etc.
First aid kits with all essential material should be kept handy in the vicinity of work, with the support team.
The communication signals should be mutually agreed and understood by all. These should be practised too to identify the difference between a quick tug and a long pull. A Few examples are given below:
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One quick tug every 5 minutes would mean everything fine
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Two quick tugs could mean that he needs something from top
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Three quick tugs could mean he wants to send something up
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Long pulling on the rope or frantic tugging means he is in trouble and needs help
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No tugs or pulls for more than 10 minutes would mean immediate assisted evacuation of the person from the space.
It is worthwhile developing a “Standard Operating Process” (SOP) for any work related to confined spaces, so that it becomes part of a standard drill by all concerned.
Part 3 of this series will have a check off list that can be consulted and confirmed before undertaking work within confined spaces.
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