Reading the result
A result within the thresholds is not an entry permit. Check other substances, measurement locations and times, ventilation, the attendant and rescue arrangements.
Legal basis
Article 618(3): oxygen ≥18% and <23.5%; carbon dioxide <1.5%; carbon monoxide <30 ppm; hydrogen sulfide <10 ppm. Work-programme, measurement and ventilation duties under Article 619 onwards also apply.
Official Korean legislationExamples
O₂ 20.9%, CO₂ 0.04%, CO 0 ppm, H₂S 0 ppm → Within four thresholds; not an entry permit.
O₂ 23.5%, CO₂ 0.04%, CO 0 ppm, H₂S 0 ppm → Fails the exclusive oxygen upper limit.
Questions
Is oxygen alone enough?
No. All four inputs are required; the work may require measurements of additional hazardous substances.
Are boundary values rounded?
The entered value is compared without rounding. Instrument error and calibration require separate assessment.
The responsible workplace professional should confirm the final assessment against the original legislation.
Gas concentration conversionChecks and records before work
Keep the gas name and unit together with where and when the measurement was taken when entering confined-space readings. A reading at the entrance does not show every condition at the actual working depth or in screened areas. Follow the site’s confined-space procedure and the measurement team’s plan for the required locations and sequence before work. If the input screen shows only one location, do not record the same result as representing other locations. Record the instrument used, the measurement time and any points that could not be measured so the next shift can distinguish older readings from current ones.
A blank field means the result is unavailable. Distinguish a measured value, a reading outside the display range and a substance that was never measured. Ask the work lead to arrange missing measurements. Check units and preserve the individual results for each location. Report a fluctuating display to the person responsible for measuring so the sampling conditions can be checked.
Time, ventilation, nearby tasks or changing contents can make an earlier reading unrepresentative. An in-range result describes the values entered. Sampling locations, ventilation, monitoring, communication and emergency readiness are separate permit checks. At handover, state the location, time, unresolved checks and changed conditions. Follow the site procedure to stop and reassess when conditions may have changed.