Confined Space Entry

Overview

Most confined-space deaths are unprotected rescuers — never enter to rescue without equipment.

Atmospheric acceptance criteria (typical)

Oxygen: 19.5–23.5%.
Flammable gas: below 10% LEL.
Toxic gases: below exposure limits.

Step-by-step procedure

Isolate the space (LOTO, line blinding).
Ventilate to clear and refresh the atmosphere.
Test the atmosphere (top, middle, bottom).
Issue the entry permit only when readings pass.
Post a trained standby attendant with an entry log.
Monitor the atmosphere continuously.
Have rescue equipment ready.
On exit, account for everyone and close the permit.

Roles & responsibilities

Role	Responsibility
Entrant	Works inside; exits on alarm.
Standby attendant	Stays at entry; raises alarm, starts rescue.
Entry supervisor	Authorizes entry; verifies tests and rescue plan.

Common mistakes to avoid

Entering to rescue without breathing apparatus.
One test then entry — monitor continuously.
Ventilating with oxygen instead of air.

Legal requirements (Thailand)

Occupational Safety, Health and Environment Act B.E. 2554 (2011) — the governing workplace-safety law in Thailand.
Ministerial Regulation on OSH for work in confined spaces B.E. 2562 (2019).

Frequently asked questions

What is Confined Space Entry?

A confined space is large enough to enter but not designed for continuous occupancy and has limited entry/exit — tanks, vessels, sumps, pits and ducts. The danger is the atmosphere: it can be oxygen-deficient, toxic or flammable, and often gives no warning. Most confined-space fatalities are would-be rescuers who rushed in unprotected.

Who is responsible?

Entrant: Works inside, wears the gas detector, exits on alarm.; Standby attendant: Stays at the entry, never enters, raises the alarm and starts rescue.; Entry supervisor: Authorizes entry, verifies tests and the rescue plan.

What are the most common mistakes to avoid?

Entering to rescue without breathing apparatus — the most common cause of multiple fatalities. Single test then entry — atmospheres change; monitor continuously. Using oxygen (not air) to ventilate — raises fire/explosion risk.

References — Company procedure; Thai confined-space regulation; OSH Act B.E. 2554.