Isolating a Confined Space: Lockout/Tagout, Blanking, Double Block and Bleed

Ventilation handles the air already in the space. Isolation stops new hazards from getting in: product flowing back through a line, steam, a mixer starting up, or an upstream flow filling a sewer. Under 1910.146(d)(3), the permit program must include procedures for isolating the permit space.

What isolation means

OSHA defines isolation as the process by which a permit space is removed from service and completely protected against the release of energy and material into the space by such means as:

• Blanking or blinding
• Misaligning or removing sections of lines, pipes or ducts
• A double block and bleed system
• Lockout or tagout of all sources of energy
• Blocking or disconnecting all mechanical linkages

Blanking and blinding

Blanking or blinding is the absolute closure of a pipe, line or duct by fastening a solid plate (a spectacle blind or skillet blind) that completely covers the bore and can withstand the maximum pressure of the line with no leakage. The blank goes at the flange closest to the space, and it must be rated for the pressure.

Double block and bleed

Double block and bleed closes a line by closing and locking or tagging two in-line valves and opening and locking or tagging a drain or vent valve between them. If the upstream valve leaks, the material drains or vents out instead of reaching the second valve and the space.

Removing or misaligning sections of line

Disconnecting a spool piece or misaligning a line creates a physical gap. Cap or plug open ends where needed, and make sure nothing can flow onto the floor outside or into the space.

Lockout/tagout of energy

Mixers, agitators, augers, conveyors, pumps, fans and electrical equipment inside or connected to the space must be de-energized and locked out under the employer's energy control procedures (29 CFR 1910.147 in general industry):

1. Notify affected employees.
2. Shut down the equipment by the normal stopping procedure.
3. Isolate all energy sources: electrical, mechanical, hydraulic, pneumatic, chemical, thermal and gravity.
4. Apply locks and tags. Each entrant can apply a personal lock, often with a group lockout box.
5. Release or restrain stored energy: bleed pressure, block parts that could fall or rotate, discharge capacitors.
6. Verify isolation: try to start the equipment, test for zero energy, then return controls to off.

Also block or disconnect mechanical linkages, such as removing a coupling or drive belt, when a motor could be energized another way.

Engulfment and flow hazards

• Lock out feed conveyors and gates that could add grain, sand or other material.
• In sewers and storm drains, plan for upstream flows from storms or discharges. The construction standard requires an early-warning system that gives entrants time to exit when engulfment is possible from upstream (1926.1204).
• Don't walk on bridged or crusted material. Use body harnesses and lifelines where engulfment is possible.

Line breaking

Line breaking is intentionally opening a pipe, line or duct that is or has been carrying flammable, corrosive or toxic material, an inert gas, or any fluid at a volume, pressure or temperature capable of causing injury. Treat it as a hazardous job in its own right: drain, depressurize, flush and verify before opening, and wear PPE for the contents.

Verifying isolation

Before the entry supervisor signs the permit:

• Walk the isolation points and confirm blanks, blinds, open drains and locks match the isolation list.
• Confirm equipment won't start (try the start button or local control).
• Confirm the space is drained, depressurized and cleaned as needed.
• Record the isolation measures on the permit, as required by 1910.146(f)(8).

Key takeaways

• Isolation protects the space from energy and material entering it.
• Accepted methods: blanking or blinding, double block and bleed, removing or misaligning lines, lockout/tagout, and disconnecting linkages.
• A single closed valve isn't isolation.
• Lock out all energy, release stored energy, and verify zero energy before entry.
• Plan for engulfment and upstream flows, and record isolation on the permit.

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1910.146 and 29 CFR 1926 Subpart AA. It does not replace the site-specific training, written program and hands-on evaluation your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.