Moisture and Humidity Risk Assessment Calculator

ANA›Life Services Authority›National Calculator Authority›Moisture and Humidity Risk Assessment Calculator

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Moisture and Humidity Risk Assessment Calculator

Evaluate moisture and humidity risk for buildings, materials, and environments using temperature, relative humidity, dew point analysis, and mold growth potential indices.

Air Temperature (°C)

Relative Humidity (%)

Surface / Wall Temperature (°C)

Exposure Duration (hours)

Material Type

Wood / Timber Concrete / Masonry Drywall / Gypsum Metal / Steel Insulation (Fibreglass/Mineral Wool)

Calculate Risk Results will appear here.

function moiCalc() { var T = parseFloat(document.getElementById('moi-temp').value); var RH = parseFloat(document.getElementById('moi-rh').value); var Ts = parseFloat(document.getElementById('moi-surface-temp').value); var dur = parseFloat(document.getElementById('moi-duration').value); var mat = document.getElementById('moi-material').value;

// --- Input validation --- if (isNaN(T) || isNaN(RH) || isNaN(Ts) || isNaN(dur)) { document.getElementById('moi-result').innerHTML = 'Please fill in all fields with valid numbers.'; return; } if (RH 100) { document.getElementById('moi-result').innerHTML = 'Relative Humidity must be between 0 and 100%.'; return; } if (T 60 || Ts 60) { document.getElementById('moi-result').innerHTML = 'Temperatures must be between -40°C and 60°C.'; return; } if (dur 8760) { document.getElementById('moi-result').innerHTML = 'Exposure duration must be between 0 and 8760 hours (1 year).'; return; }

// ----------------------------------------------------------------------- // 1. Dew Point Temperature (Magnus formula — Lawrence 2005) // Td = (243.04 * [ln(RH/100) + (17.625T)/(243.04+T)]) // / (17.625 - [ln(RH/100) + (17.625T)/(243.04+T)]) // ----------------------------------------------------------------------- var a = 17.625; var b = 243.04; // °C var lnRH = Math.log(RH / 100.0); var gamma = lnRH + (a * T) / (b + T); var Td = (b * gamma) / (a - gamma);

// ----------------------------------------------------------------------- // 2. Saturation Vapour Pressure (Buck equation, kPa) // es(T) = 0.61121 * exp((18.678 - T/234.5) * T / (257.14 + T)) // ----------------------------------------------------------------------- function es(temp) { return 0.61121 * Math.exp((18.678 - temp / 234.5) * temp / (257.14 + temp)); } var esAir = es(T); var esSurface = es(Ts); var eActual = (RH / 100.0) * esAir; // actual vapour pressure (kPa)

// ----------------------------------------------------------------------- // 3. Surface Relative Humidity (RH_s) // RH_s = (e_actual / es(Ts)) * 100 // ----------------------------------------------------------------------- var RH_s = (eActual / esSurface) * 100.0; if (RH_s > 100) RH_s = 100.0; // cap at 100% (condensation occurring)

// ----------------------------------------------------------------------- // 4. Condensation Risk // Condensation occurs when surface temp = 80% sustained // MGRI = RH_s_factor * duration_factor * material_factor // Scale 0–10 // ----------------------------------------------------------------------- var matFactor = { wood: 1.0, drywall: 0.95, insulation: 0.85, concrete: 0.60, metal: 0.30 }; var mf = matFactor[mat];

// RH_s factor: 0 below 70%, linear 70–80%, accelerated above 80% var rhsFactor; if (RH_s 1) rhsFactor = 1;

// Duration factor: log scale, 24 h = 0.3, 168 h = 0.6, 720 h = 1.0 var durMold = dur 100) ORS = 100;

// ----------------------------------------------------------------------- // 9. Risk Classification // ----------------------------------------------------------------------- function classify(score) { if (score 70) recs.push('Reduce indoor relative humidity below 60% using dehumidification or improved ventilation.'); if (RH_s >= 80) recs.push('Surface relative humidity exceeds 80% — mold growth conditions are present. Inspect and treat surfaces.'); if (MGRI >= 5) recs.push('High mold growth risk index detected. Consider anti-mold coatings and moisture barriers for ' + mat + '.'); if (CRI >= 5 && mat === 'metal') recs.push('Significant corrosion risk for metal surfaces. Apply protective coatings or galvanisation.'); if (dur > 168) recs.push('Prolonged exposure (>' + dur.toFixed(0) + ' h) significantly amplifies damage risk. Address moisture source promptly.'); if (recs.length === 0) recs.push('Conditions are within acceptable limits. Continue routine monitoring.');

// ----------------------------------------------------------------------- // Output // ----------------------------------------------------------------------- var html = '### Moisture & Humidity Risk Assessment Results '; html += ''; html += 'ParameterValue';

function row(label, val, unit, highlight) { var bg = highlight ? 'background:' + highlight + '22;' : ''; return '' + label + '' + val + ' ' + unit + ''; }

html += row('Air Temperature', T.toFixed(1), '°C'); html += row('Relative Humidity (Air)', RH.toFixed(1), '%'); html += row('Surface Temperature', Ts.toFixed(1), '°C'); html += row('Dew Point Temperature', Td.toFixed(2), '°C', condensationRisk ? '#c0392b' : null); html += row('Condensation Margin (Ts − Td)', condensationMargin.toFixed(2), '°C', condensationRisk ? '#c0392b' : (condensationMargin = 80 ? '#c0392b' : (RH_s >= 70 ? '#e67e22' : null)); html += row('Humidity Index (HI)', HI.toFixed(1), '/ 100'); html += row('Mold Growth Risk Index', MGRI.toFixed(2), '/ 10'); html += row('Corrosion Risk Index', CRI.toFixed(2), '/ 10'); html += '';

html += ''; html += 'Overall Risk Score: ' + ORS.toFixed(1) + ' / 100'; html += 'Risk Level: ' + orsClass.label + ''; html += '';

html += ''; html += 'Mold Risk' + moldClass.label + '' + (MGRI * 10).toFixed(1) + ' / 100'; html += 'Corrosion Risk' + corrClass.label + '' + (CRI * 10).toFixed(1) + ' / 100'; html += 'Condensation' + (condensationRisk ? 'Active' : 'None') + ''; html += '';

html += ''; html += 'Recommendations:'; recs.forEach(function(r) { html += '' + r + ''; }); html += '';

document.getElementById('moi-result').innerHTML = html; }

#### Formulas Used

1. Dew Point (Magnus / Lawrence 2005): γ(T, RH) = ln(RH/100) + (17.625 × T) / (243.04 + T) Td = 243.04 × γ / (17.625 − γ) [°C]

2. Saturation Vapour Pressure (Buck equation): es(T) = 0.61121 × exp[(18.678 − T/234.5) × T / (257.14 + T)] [kPa]

3. Actual Vapour Pressure: e = (RH/100) × es(Tair)

4. Surface Relative Humidity: RHs = (e / es(Tsurface)) × 100 [%]

5. Humidity Index (HI): HI = 0.5 × RH + 0.3 × RHs + 0.2 × min(duration/720, 1) × 100

6. Mold Growth Risk Index (MGRI, 0–10): MGRI = RHs-factor × duration-factor × material-factor × 10 (Based on ASHRAE 160 / ISO 13788 mold growth thresholds; RHs ≥ 80% critical)

7. Corrosion Risk Index (CRI, 0–10): CRI = (RHs/100)² × min(duration/720, 1) × 10 × material-factor (Based on ISO 9223 atmospheric corrosion classification)

8. Overall Risk Score (ORS, 0–100): ORS = 0.40 × HI + 0.40 × (MGRI × 10) + 0.20 × (CRI × 10)

#### Assumptions & References

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