Chemical Exposure Limit Calculator
ANA›Life Services Authority›National Calculator Authority›Chemical Exposure Limit Calculator
.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
Chemical Exposure Limit Calculator
Calculate Time-Weighted Average (TWA) exposure, Hazard Quotient (HQ), and determine if workplace chemical exposure is within safe limits based on OSHA/NIOSH/ACGIH standards.
### Exposure Measurement Inputs
Number of Exposure Samples (1–10)
Total Work Shift Duration (hours)
### Occupational Exposure Limit
OEL Standard
Custom / Manual Entry OSHA PEL (8-hr TWA) NIOSH REL (10-hr TWA) ACGIH TLV (8-hr TWA)
OEL Value (ppm or mg/m³)
OEL Unit
ppm (parts per million) mg/m³ (milligrams per cubic meter)
### Extended Shift Adjustment (Optional)
Apply Brief & Scala Model for extended shifts?
No – use standard OEL Yes – adjust OEL for extended shift
Calculate Exposure
#### Formulas Used
Time-Weighted Average (TWA):
TWA = Σ(Cᵢ × Tᵢ) / Tshift
Where Cᵢ = concentration during period i, Tᵢ = duration of period i (hours), Tshift = total shift duration (hours).
Hazard Quotient (HQ):
HQ = TWA / OEL
HQ < 1 → Acceptable exposure; HQ ≥ 1 → Exceeds limit (action required).
Brief & Scala Extended Shift Adjustment:
RF = (8/h) × (24 − h) / 16
Adjusted OEL = OEL × RF
Where h = hours worked per shift. Valid for shifts between 8 and 12 hours.
Percent of OEL:
% OEL = (TWA / OEL) × 100
#### Assumptions & References
(function() { const OEL_REFS = { osha_pel: { label: "OSHA PEL (8-hr TWA)", note: "OSHA Permissible Exposure Limit — legally enforceable 8-hour TWA. Source: 29 CFR 1910.1000 Table Z-1. Enter the specific chemical's PEL value above.", basis: 8 }, niosh_rel: { label: "NIOSH REL (10-hr TWA)", note: "NIOSH Recommended Exposure Limit — 10-hour TWA, 40-hr/week. Source: NIOSH Pocket Guide to Chemical Hazards. Enter the specific chemical's REL value above.", basis: 10 }, acgih_tlv: { label: "ACGIH TLV-TWA (8-hr TWA)", note: "ACGIH Threshold Limit Value — 8-hour TWA, 40-hr/week. Source: ACGIH TLVs and BEIs. Enter the specific chemical's TLV-TWA value above.", basis: 8 }, custom: { label: "Custom OEL", note: "", basis: 8 } };
function cheUpdateSamples() { const n = parseInt(document.getElementById('che-num-samples').value) || 1; const clamped = Math.min(Math.max(n, 1), 10); const container = document.getElementById('che-samples-container'); container.innerHTML = ''; for (let i = 1; i Sample ${i} Concentration (ppm or mg/m³)
Duration (hours)
`; } }
function cheToggleOEL() { const type = document.getElementById('che-oel-type').value; const noteBox = document.getElementById('che-oel-ref-note'); if (type !== 'custom' && OEL_REFS[type]) { noteBox.style.display = 'block'; noteBox.innerHTML = '' + OEL_REFS[type].label + ': ' + OEL_REFS[type].note; } else { noteBox.style.display = 'none'; } }
function cheCalc() { const resultDiv = document.getElementById('che-result'); resultDiv.innerHTML = '';
const n = Math.min(Math.max(parseInt(document.getElementById('che-num-samples').value) || 1, 1), 10); const shiftHours = parseFloat(document.getElementById('che-total-shift').value); const oelValue = parseFloat(document.getElementById('che-oel-value').value); const oelUnit = document.getElementById('che-oel-unit').value; const oelType = document.getElementById('che-oel-type').value; const applyBrief = document.getElementById('che-apply-brief').value === 'yes';
// Validation const errors = []; if (isNaN(shiftHours) || shiftHours 24) errors.push("Total shift duration must be between 0.5 and 24 hours."); if (isNaN(oelValue) || oelValue shiftHours + 0.001) { errors.push("Sum of sample durations (" + sumDurations.toFixed(2) + " hrs) exceeds total shift duration (" + shiftHours.toFixed(2) + " hrs)."); }
if (errors.length) { resultDiv.innerHTML = 'Input Errors:' + errors.map(e => '').join('') + ''; return; }
// TWA Calculation let weightedSum = 0; for (let i = 0; i 12) { briefScalaNote = '⚠️ Brief & Scala model is only validated for shifts between 8 and 12 hours. Adjustment not applied.'; adjustedOEL = oelValue; } else { rfValue = (8 / shiftHours) * ((24 - shiftHours) / 16); adjustedOEL = oelValue * rfValue; briefScalaNote = `Brief & Scala Reduction Factor (RF): (8 / ${shiftHours}) × (24 − ${shiftHours}) / 16 = ${rfValue.toFixed(4)}
Adjusted OEL: ${oelValue} × ${rfValue.toFixed(4)} = ${adjustedOEL.toFixed(4)} ${oelUnit === 'ppm' ? 'ppm' : 'mg/m³'}
`; } }
// Hazard Quotient const hq = twa / adjustedOEL; const pctOEL = hq * 100;
// Risk classification let riskClass, riskLabel, riskAdvice; if (hq Sample ${i+1} ${concentrations[i].toFixed(4)} ${durations[i].toFixed(2)} ${(concentrations[i] * durations[i]).toFixed(4)} ${contrib} `; }
// Unmonitored time
const unmonitoredTime = shiftHours - sumDurations;
let unmonitoredNote = '';
if (unmonitoredTime > 0.01) {
unmonitoredNote = ⚠️ Note: ${unmonitoredTime.toFixed(2)} hours of the shift are unmonitored.
The TWA assumes zero exposure during unmonitored periods, which may underestimate actual exposure.;
}
const unitLabel = oelUnit === 'ppm' ? 'ppm' : 'mg/m³'; const oelTypeLabel = OEL_REFS[oelType] ? OEL_REFS[oelType].label : 'Custom OEL';
resultDiv.innerHTML = `
### ${riskLabel}
${riskAdvice}
${unmonitoredNote}
### Results Summary
ParameterValue Time-Weighted Average (TWA)${twa.toFixed(4)} ${unitLabel} OEL Standard Used${oelTypeLabel} OEL Value (entered)${oelValue.toFixed(4)} ${unitLabel} Adjusted OEL (after B&S, if applied)${adjustedOEL.toFixed(4)} ${unitLabel} Hazard Quotient (HQ = TWA / OEL)${hq.toFixed(4)} % of OEL${pctOEL.toFixed(2)}% Total Shift Duration${shiftHours.toFixed(2)} hours Total Monitored Duration${sumDurations.toFixed(2)} hours Unmonitored Duration${unmonitoredTime.toFixed(2)} hours (assumed 0 exposure)
${briefScalaNote}
### Sample Breakdown
Sample Concentration (${unitLabel}) Duration (hr) C × T TWA Contribution (${unitLabel})
${tableRows}
Total — ${sumDurations.toFixed(2)} ${weightedSum.toFixed(4)} ${twa.toFixed(4)}
### Calculation Steps
Step 1 – Weighted Sum: Σ(Cᵢ × Tᵢ) = ${weightedSum.toFixed(4)} ${unitLabel}·hr
Step 2 – TWA: ${weightedSum.toFixed(4)} / ${shiftHours.toFixed(2)} hr = ${twa.toFixed(4)} ${unitLabel}
${applyBrief && rfValue !== null ? `Step 3 – B&S Adjusted OEL: ${oelValue} × ${rfValue.toFixed(4)} = ${adjustedOEL.toFixed(4)} ${unitLabel}
` : ''} ${applyBrief && rfValue !== null ? 'Step 4' : 'Step 3'} – Hazard Quotient: ${twa.toFixed(4)} / ${adjustedOEL.toFixed(4)} = ${hq.toFixed(4)}
Disclaimer: This tool is for educational and preliminary assessment purposes only. Always consult a Certified Industrial Hygienist (CIH) and refer to current regulatory standards for compliance decisions. `; }
// Initialize window.cheCalc = cheCalc; window.cheUpdateSamples = cheUpdateSamples; window.cheToggleOEL = cheToggleOEL; cheUpdateSamples(); })();
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