The vessel has been properly prepared and the temperature should be as near ambient as possible.
Vessel should be isolated of blinds installed close to the vessel.
The vessel has been satisfactorily gas freed and tested.
Provide adequate ventilation. Keep all possible man heads open.
Limit the number of men working inside.
Wear safety hats while working inside vessel.
Ensure that no material can fall down from people working above.
Only approved reduced voltage extension lights (24 volts) will be allowed for use inside vessel.
A standby should be located outside the vessel at the man head.
Provide one flashlight for men working inside each location.
Prepare a specific permit for buttoning up of vessel after work is completed. This is to ensure that no one is to ensure that no one is left inside vessel and no material is left behind. One responsible person must inspect vessel prior to buttoning up and stay at the man head till the man head is buttoned up at least on four bolts.
Important points to be conserved for correct gas testing in confined space:
Meter Check – Check voltage, No leak on connection, daily checking standardization (calibration).
Handling & storage – Not to be left outside – No contact with water, dropping etc.
Gas Testing – Not to be done with steam, N2 or hot – should be near ambient temperature.
Gas Testing Safety – Long drums, tanks, etc. – use fresh air nose mask & standby.
Look for other hazards- Deposits, heavy oils shall not give reading in meter.
If the sample is to rich to explode, the meter hand will first swing sharply to the red end of the scale and will than fall to zero or below, giving no further indication.
For hot work meter should read Zero.
No entry is permitted inside vessels beyond 20 % (reading of 0.2 in the meter lower flammable (Explosive) limit.
Use multi gas detector.
For entry inside vessels oxygen content should be not less than 19.5% (19.5 to 23.5%).
A) Hydrogen – Gives 25% lower than actual amount of gas present- use combustible Gas indicator especially calibrated for Hydrogen. B) Hydrogen Sulphide – H2S mixed with other flammable gasses – No material calibration change but H2S by itself gives an indication of 10% lower than actual amount of gas present.
Safety precautions for hot work in confined space:
Conditions must be free from combustible flammable gases, liquids or solids.
Conditions must be free from asphyxiating and toxic gases and vapours and corrosive chemicals.
All lines to the vessel must be blinded, if the lines cannot be blinded they should be disconnected and the open are to be made safe by installing blond flanges.
Where exposed flame work or electric welding under hot work & safety permit is in progress, no other hazardous work will be permitted (e.g. cold work of opening lines/equipment that have contained hydrocarbons).
All blinds shall be inserted as close to the container as possible.
In the event a line cannot be blinded, the equipment with which that line connects must also comply with the standards limiting the work that may be permitted.
If changes are made on lines and valve that would in any manner change the conditions that were existing at the time of issuing the Permit, the Permit shall be null and void and another must be obtained before the work for which the permit was issued is resumed.
In some cases, especially vessels that might have contained lighter products, it might be necessary to call for follow-up gas testes after work has commenced. Such tests should be arranged by the authorized personnel and when necessary.
Take adequate precautions while doing hot work. Follow conditions stipulated in hot work and safety permit.
Keep sewer openings and sewer vents properly covered.
Have running water so that sparks will get extinguished.
In certain locations it may be necessary to cover with asbestos cloth or asbestos/aluminium sheets to arrest sparks.
Ensure fire protection equipment is nearby.
If any unusual conditions such as oil/gas leak is noticed or fire alarm is sounded, stop hot work immediately any report to process personnel.