Confined Space Isolation Requirements in Plants

Confined Space Isolation Requirements

1. Prior to entry, the confined space shall be isolated from all hazard sources in accordance with 25-010532.
2. Isolate all lines in and out of the permit-required space by blinding, disconnecting or removing a section of line, or providing a double block and bleed. Special precautions are required when using double block and bleed isolation for confined space entry. See paragraph (Double Block and Bleed) for details on isolation strategies. See paragraph (Controlling Risks Associated With Live Lines Contained In Confined Spaces) for details on evaluating and controlling the hazards associated with live lines in a confined space.
3. Typically, confined spaces can be isolated in a number of ways. Preference must be given to the safest method of isolation based on the space’s construction. In order of decreasing levels of safety, they are:
   • Remove piping spool (physical disconnection) and fit blank(s)/blind(s)
   • Fit blank(s)/blind(s).
   • Double Block Valve and Bleed Valve.
   • Blinds shall have a pressure rating equal to the line source. Blinds must be secured and sealed. Blinds shall be locked and tagged. Blinds may be locked into place by wrapping chain around the blind and flange and locking into place.
   • Physically disconnecting and removing a section of line is acceptable isolation. Disconnected lines must be capped or misaligned so contents of the process side cannot migrate into the confined space. The confined space side of a physical disconnect must have a lock and tag installed (i.e., lock installed through bolt hole of a flange) to prevent inadvertent reconnection.
   • Blind and isolation lists shall be used when preparations are made to enter process equipment.
   • Blinding at the closest flange point is the preferred location for blinds. Blinding can, however, be installed at any point on the line as long as the remaining portion of the line (connected to the confined space) is properly cleaned and purged to make it safe and remove any residual contaminants.
   • Double Block and Bleed may be used as an isolation when design and construction of a confined space precludes the practical implementation of other isolation methods (e.g., blinding, disconnecting of lines). Double block and bleed may only be used as a method of isolation when alternatives have been considered and are not feasible. See paragraph 5.5.4 for details.

4. Double Block and Bleed

   • Only after alternative methods of isolation have been considered (i.e., blinding, disconnecting of lines) may double block and bleed be used for isolation of confined spaces (both permit and non-permit) under the following conditions:
     • The bleed valve shall be initially monitored, upon isolation, for leakage through either of the isolation block valves.
     • Any leakage through the block valves indicates that the block valve is not effectively isolating the space and entry cannot proceed until effective isolation is obtained through the block valves or an alternative method of isolation (i.e., blinding, disconnecting of lines).
     • Bleed valves must be checked to ensure that they can effectively bleed off pressure that may subsequently leak through the block valves. Bleed valves shall be checked for buildup of scale or corrosion.
     • Double block and bleed may not be used for materials that polymerize (or freeze) at ambient temperatures. Materials that polymerize (or freeze) at ambient temperature make the use of double block and bleed an ineffective isolation method because these materials can obstruct the bleed valve.
     • Both block valves and the bleed valve shall be locked in the appropriate isolation position.

5. Controlling Risks Associated With Live Lines Contained In Confined Spaces

   1. Live process lines contained within confined spaces present a unique hazard that must be eliminated or controlled during confined space entries. Even though the actual space being entered has been assessed and determined to be safe for entry, live process lines within a space may contain fluids, that if introduced into the entry space by leak or line failure, can cause serious injury to entrants.
      • Lines must be evaluated considering the material in the line, the condition and number of connections, and the potential for hazardous leaks or releases.
      • Lines that do not contain mechanical joints, flanges, or valves, e.g., all welded construction, are not usually considered a hazard. Consideration must be given to conditions that might exist where as these lines might be considered a hazard (e.g., hot work or excavation adjacent to the lines, lines struck by tools or equipment).
      • Whenever practical, live lines should be isolated and de-energized to eliminate the possibility of leakage or failure.
      • If complete isolation and de-energization is not practical or if the integrity of live lines is known to be compromised (i.e., leak detection or repair operations) and the process is not isolated, controls must be implemented to ensure that the leaking contaminants do not endanger the entrants.
   2. Methods of control to consider include:
      • o  Consider the space an IDLH entry and implement 25-010542.
      • o  Lower the pressure of the process to reduce the leak rate or possibility of line failure.
      • o  Provide adequate ventilation and continuous atmospheric monitoring to assure safe entry conditions.
      • Jacket spaces on jacketed vessels and cooling coils are considered part of a confined space. It is permissible, with special planning, to circulate cold water through a vessel jacket or cooling coils during the vessel entry, in order to reduce the heat stress on the Entrants.
      • Cryogenic equipment enclosures (columns, cans, and boxes) may not be practical for isolation. In most cases, the only obvious method of isolation is to shut off/disconnect the nitrogen purge. Many times air separation plants are operating while personnel try to find leaks, making isolation of the leak impractical. Extra precautions, e.g., opening several panels to get cross ventilation, use of air movers, etc., must be considered when completing the entry permit.

6. Isolation of Nozzles and Dead-Headed Connections

   • Drain nozzles or other dead-headed connections to the equipment being entered may have to be plugged or cut and blinded to ensure adequate isolation from the potential for migrating fluid back into the system.