Confined-Space Hot Work Permit Sign-Off
A maintenance crew is repairing a crack in the shell of a 2.4 m diameter, 3 m long steel tank that last held diesel fuel. The tank has been drained, water-washed, and purged with air for 4 hours. A calibrated four-gas monitor at the entry reads O2 19.0%, LEL 0%, CO 30 ppm, H2S 0 ppm. A single 200 mm flexible duct supplies air at the bottom; the welder is working 2.5 m from the opening. The welder reports a mild headache and dizziness after 20 minutes of tack welding with E7018. The hot work permit is on the clipboard, and the supervisor asks you to sign it so the root pass can be completed before the shift ends. The tank has one 450 mm manhole; no rescue team is on site, but a standby person is at the opening with a radio.
1. Should you sign the hot work permit? Explain the specific readings and symptoms that drive your decision.
Read the worked answer
No. The entry reading of 19.0% O2 is below the common 19.5% minimum for confined-space entry, and the welder's headache and dizziness are consistent with oxygen deficiency or exposure to welding fumes/CO. The CO reading of 30 ppm is below the 50 ppm OSHA PEL, but a single entry reading is not enough: the sample was taken at the manhole, not at the welder's breathing zone 2.5 m inside. The duct at the bottom may short-circuit air along the floor and leave the upper breathing zone poorly ventilated. The LEL of 0% and H2S of 0 ppm do not offset the O2 deficit. Signing would authorize entry under conditions that already show a measurable oxygen deficiency and a symptomatic worker.
2. What immediate actions should be taken before any further welding?
Read the worked answer
Stop work, evacuate the tank, and account for all personnel. Increase ventilation and re-test at the work location, not just the entry, with a calibrated monitor. Do not re-enter until O2 is at least 19.5% and the atmosphere is stable. The symptomatic welder should be evaluated and not sent back in. If ventilation cannot maintain acceptable O2 and fume levels, use supplied-air respiratory protection appropriate for the hazard. The standby person must remain at the opening with a radio, and a rescue plan with trained rescuers must be in place before re-entry. The permit should be reissued only after the space is re-evaluated.
3. What changes to the ventilation and monitoring plan would you require?
Read the worked answer
Move the supply air to sweep the breathing zone rather than the floor, and add exhaust at the opposite side to create cross-flow. Use continuous monitoring with alarms for O2, LEL, CO, and H2S, with the sensor at the welder's location. Test before entry, after any break, and at least hourly or continuously. The 200 mm duct may be too small for the volume; calculate or verify airflow. Keep the manhole unobstructed, post an attendant, and limit entry to essential personnel. If the tank has sludge or scale that can release hydrocarbons, re-test LEL after disturbance.