Gas concentration conversion
Convert ppm, vol% and %LEL. NIST SP 330. This does not establish safety.
Reference table
These are basic criteria. Check scope, exceptions, qualifications and the original wording. Korean text in parentheses is authoritative.
Expand / collapse reference table
| Input | Relationship | Converted value |
|---|---|---|
| 1 vol% | vol% × 10,000 | 10000 ppm |
| 500 ppm | ppm ÷ 10,000 | 0.05 vol% |
| Example LEL 5 vol%, concentration 0.5 vol% | vol% ÷ LEL(vol%) × 100 | 10 %LEL |
Worked examples
500 ppm → 0.05 vol%
1 vol% → 10,000 ppm
Frequently asked questions
How many ppm is 1 vol%?
For volume fractions, it is 10,000 ppm. This follows the percent and ppm definitions in NIST SP 330.
Are %LEL and vol% the same?
No. %LEL is a fraction of the gas-specific lower explosive limit. Verify the LEL before using the relationship.
Does the conversion establish safe entry?
No. Check sensors, calibration, target gas, oxygen deficiency and toxicity separately, as discussed in OSHA instrumentation guidance.
Does it apply detector correction factors?
No; it changes units only. Follow the manufacturer’s instructions for the sensor and calibration gas.
Technical principle and management judgement
- ppm ÷ 10,000 → vol%
- vol% ÷ LEL(vol%) × 100 → %LEL
Percent means parts per hundred; ppm means parts per million. Thus 1 vol% is 10,000 ppm by definition. %LEL expresses a fraction of the lower explosive limit, not the gas volume fraction itself. No preset substance values are supplied.
Check gas identity, calibration gas, sensor response and the source of the LEL. Mixed gases, oxygen deficiency, toxicity and instrument cross-sensitivity cannot be judged from this conversion.
Reference only. Check original sources and the responsible authority for final decisions.
NIST SP 330 · Percentage and parts per million
For volume fractions, 1 vol% = 10,000 ppm. %LEL = vol% / LEL(vol%) × 100; the inverse is vol% = %LEL × LEL(vol%) / 100. Use the same gas and a supported LEL value. These equations convert units; they do not correct a detector reading.
Calibration and correction factors
A conversion is meaningful only when the measured concentration is valid. A bump test checks sensor response and alarms; it is not an adjustment of measurement accuracy. Follow the instrument manufacturer’s procedure for calibration checks and adjustment using the specified test gas.
OSHA · Calibrating and Testing Direct-Reading Portable Gas Monitors
When the measured gas differs from the calibration gas, the sensor response may differ. Use only the manufacturer’s correction chart for that instrument, sensor and calibration gas. This converter does not apply correction factors. It does not assess toxicity, oxygen deficiency, mixtures or safe entry.
OSHA Technical Manual · Direct-reading instrumentation
The OSHA links are US technical guidance, not a statement of Korean legal duties.
Original sources and applicable legislation
Related reading
Checks and records before work
Check what the instrument displays before converting concentration units. For the same substance in the same mixture, one volume percent equals ten thousand parts per million by volume. Match the displayed unit to the calculator field. Do not directly enter a mass-based concentration or a value with no substance identity, even if the number looks the same. Keep the substance, unit, location and time with the result so the calculation can be checked later.
Percent of the lower explosive limit is different from the gas volume percentage in air: it expresses concentration relative to the limit for a particular substance. The conversion therefore requires both the substance identity and its lower explosive limit. The same volume concentration can represent different percentages for different gases. Obtain the substance-specific limit from the safety data sheet or verified technical information, and do not mix values with different units in one entry. For a mixture or an unidentified gas, do not finalize a result by converting it using a single substance's value.
A combustible gas reading can depend on the calibration gas and sensor response. If the field gas differs from the calibration gas, consult the instrument documentation for applicable conditions. Do not insert an arbitrary correction value and present the result as an accurate actual concentration. Do not decide entry into a work area or cancellation of an alarm from the calculated value alone; also check the actual measurement location and time, instrument conditions and site entry procedure. If the source of a number is unclear, retrieve the original display and substance information before repeating the calculation.