Safety Planning for Confined Space Entry During Tank Cleaning
A 50,000-gallon API 650 tank that previously stored gasoline is scheduled for internal inspection and cleaning. The tank is 30 feet diameter and 20 feet high, with a single manway at the bottom. The cleaning will involve removing sludge and scale using high-pressure water jets and hand tools. The tank has been drained and ventilated for 24 hours with a blower. Initial gas readings: LEL 15%, O2 19.5%, H2S 5 ppm, benzene 0.5 ppm. The confined space entry will last 8 hours per day for 3 days. Two workers and one attendant will be involved. The company has a written confined space program but no specific rescue plan for this tank.
1. Identify the hazards and determine if the space is safe for entry. What additional controls are necessary before entry?
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Hazards: (1) Flammable atmosphere: LEL 15% exceeds the 10% threshold for entry; must be reduced to <10% LEL. (2) Oxygen deficiency: 19.5% is at the lower limit; should be 19.5-23.5%, but with ventilation it may be acceptable; however, continuous monitoring required. (3) H2S at 5 ppm is below the 10 ppm TWA but above the 5 ppm ceiling? Actually, ACGIH TLV is 1 ppm TWA, so 5 ppm is above TLV; need respiratory protection. (4) Benzene at 0.5 ppm is below the 1 ppm TWA but still requires monitoring; benzene is a carcinogen. (5) Physical hazards: high-pressure water jets, slips, falls, electrical. The space is not safe for entry as is. Controls: (1) Continue ventilation until LEL <10% and H2S <1 ppm; use continuous gas monitoring with alarms. (2) Implement a written rescue plan with retrieval systems (tripod, winch) and trained rescue personnel on site. (3) Use appropriate PPE: supplied-air respirators if benzene or H2S present, chemical-resistant clothing. (4) Lockout/tagout of all energy sources. (5) Ensure communication equipment. (6) Atmospheric testing before and during entry. (7) Permit-required confined space entry permit with all signatures.
2. Develop a rescue plan outline and specify the required equipment and training for the rescue team.
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Rescue plan outline: (1) Pre-entry briefing with all personnel. (2) Designate a rescue team (at least two trained rescuers) on standby outside the tank. (3) Retrieval system: tripod with winch and full-body harness for each entrant. (4) Communication: radios or voice. (5) Emergency procedures: attendant initiates rescue, calls for help, and if safe, performs non-entry rescue. (6) Medical response: call 911 and provide first aid. Equipment: (1) Tripod/winch rated for confined space rescue. (2) Full-body harnesses with retrieval lines. (3) Supplied-air respirators (SAR) with escape bottles for rescuers. (4) Gas detectors for rescuers. (5) First aid kit and AED. (6) Lighting. Training: rescuers must be trained in confined space rescue, first aid/CPR, and use of retrieval equipment. Also, conduct a practice drill before entry. Ensure the rescue plan is reviewed by a safety professional.