Occupational hygienists, industrial hygienists, OHS consultants, safety officers, and environmental health professionals. The tools assume baseline familiarity with occupational health concepts and the relevant standards; they are not designed for untrained lay use.

Students and practitioners learning a new domain will find the tools useful for checking their manual calculations, but should work through the underlying standard alongside the tool rather than treating the output as a substitute for understanding the methodology.

All tools are currently free to use. Registration with a valid email address is required. A freemium model is planned — a core set of tools will remain free, with additional tools and features available on paid plans. Pricing details will be announced before any changes take effect.

No. All calculations run in your browser. Data you enter is not transmitted to any server and is not stored or logged. If you close or refresh the page, the data is gone. This applies to all tools.

Exactus Labs is a specialist tools project built by an occupational health and hygiene professional with a background in industrial hygiene practice. The goal is to reduce the time practitioners spend rebuilding the same spreadsheets and reduce the quiet errors that accumulate when those spreadsheets are copied between jobs.

A few common reasons:

Different standards. Many calculations exist in multiple versions (OSHA, NIOSH, ACGIH, Safe Work Australia), and they use different exchange rates, criterion levels, or reference periods. Check which standard your spreadsheet implements.

Rounding. Rounding differences accumulate across multi-step calculations, particularly for logarithmic noise calculations. Exactus Labs tools carry full precision throughout and round only at the final output stage.

Standard revision. The tool may implement a more recent version of a standard than your spreadsheet. Each tool page states the exact standard and revision it implements.

If none of these explain the discrepancy, email [email protected] with the inputs, your result, and the standard you are using.

These tools are calculation aids. Outputs can support your professional assessment but are not a substitute for it. Whether a result is appropriate for regulatory purposes depends on your jurisdiction, the standard your regulator requires, and your professional judgement.

Validate outputs against your measurements and site conditions before relying on them in formal documentation. Each tool states the validity limits of the calculation; work within those limits.

Where standards disagree on a material point (exchange rates, criterion levels, threshold values), the tool reports all of them rather than choosing silently. This is deliberate. Picking one without disclosure is how spreadsheet errors go unnoticed for years.

The displayed results make the disagreement visible. If your jurisdiction or client requires a specific standard, use that column; but seeing the others lets you understand the margin.

IDLH (Immediately Dangerous to Life or Health) is a NIOSH concentration above which immediate escape becomes impaired or irreversible health effects occur. It is an emergency ceiling used for respirator selection and rescue planning — not a daily exposure standard. An OEL (TWA) is the concentration considered safe for routine 8-hour exposure. IDLH values are typically 10–100× higher than the corresponding OEL.

When the odour detection threshold of a substance is higher than its OEL, a worker may be overexposed before they can smell anything. The warning flag appears when this condition applies. It does not mean the substance is odourless — it means the nose cannot be trusted as an exposure alarm for that substance at relevant concentrations.

Skin notation indicates that the substance can be absorbed through intact skin in quantities that contribute meaningfully to total body burden. For these substances, controlling airborne exposure alone is insufficient — glove selection, skin contact prevention, and hygiene practices are also required. The notation appears in standards such as ACGIH TLV, NIOSH REL, and EH40.

Dilution ventilation is appropriate for substances with OELs above approximately 50 ppm (low to moderate toxicity), where the generation rate is low and relatively uniform, and where workers are not close to the source. Local exhaust ventilation (LEV) is preferred for highly toxic substances, carcinogens, sensitisers, or whenever contaminants are generated at a concentrated point source. LEV is more energy-efficient because it removes contaminants before they disperse.

The mixing factor k (range 1-10) accounts for the fact that real rooms do not mix air perfectly. A value of 1 assumes perfect uniform mixing — a theoretical ideal. In practice, factors of 3-5 are used for reasonably well-designed ventilation systems, and 7-10 for rooms with poor air distribution, strong cross-draughts, or where the substance is highly hazardous. Higher k values result in higher required airflow to achieve the same target concentration.

Use the Mixture Assessment tab when workers are simultaneously exposed to two or more substances that act on the same target organ or by the same biological mechanism — for example, a mixture of organic solvents that all cause central nervous system depression (toluene, xylene, ethylbenzene). In that case, the additive model applies: the Hazard Index (HI = sum of Ci/OELi) tells you whether the combined exposure exceeds the mixture equivalent OEL. If substances have completely different targets (e.g. one causes liver toxicity and another causes skin sensitisation), assess them independently on the Single Chemical tab.

Dose is a dimensionless percentage: 100% means the worker has received the full permissible daily exposure. TWA (time-weighted average) is the equivalent continuous sound level over an 8-hour reference period, expressed in dB(A). They represent the same exposure in different units: dose is better for compliance checks (is it over 100%?), TWA is better for comparison to OELs expressed in dB(A).

The mathematical relationship between them depends on the criterion level and exchange rate used by the relevant standard.

These bodies use different exchange rates and criterion levels, which produce genuinely different numbers from identical inputs.

OSHA uses a 5 dB exchange rate (a doubling of dose for every 5 dB increase) and a 90 dB(A) criterion level. NIOSH and ACGIH both use a 3 dB exchange rate and an 85 dB(A) criterion level. The 3 dB rate is based on equal energy principles and is considered more protective. The 5 dB rate reflects a regulatory compromise from 1971 that has not been revised.

The difference is not a calculation error; it reflects a genuine and long-standing regulatory disagreement. The tool reports all three so you can see which is most stringent for your scenario.

The tool uses the SNR (Single Number Rating) or SLC80 method depending on the standard selected. It calculates the protected exposure level by subtracting an adjusted attenuation value from the measured A-weighted or C-weighted level, then compares that to the relevant OEL.

The adequacy result tells you whether the protector provides sufficient attenuation for the measured environment, not whether it is being worn correctly or achieving rated attenuation in practice. Real-world attenuation is typically lower than rated values due to fit, hygiene, and compliance factors.

The tool implements ISO 9613-2, which calculates the attenuation of outdoor sound propagation from a source to a receiver. The calculation starts with the source sound power level (L_W) and applies a series of corrections: geometric spreading (inverse square law for point sources, cylindrical spreading for line sources), atmospheric absorption, ground effect, and optional barrier insertion loss.

Point sources are modelled as omnidirectional emitters (e.g. a piece of plant or machinery). Line sources (e.g. a road, pipeline, or conveyor) are modelled as a continuous series of point sources, producing 3 dB of attenuation per doubling of distance rather than the 6 dB from a point source.

The result is the estimated A-weighted sound pressure level at the receiver. All inputs are approximate engineering estimates; the output is a planning tool, not a substitute for receptor-point measurement.

A single dB(A) reading is adequate for most routine compliance checks. Octave band analysis (OBA) is needed when you want to understand the frequency content of the noise, which matters in three common situations.

First, hearing protector selection using the H/M/L method requires the C-minus-A difference: if C minus A is less than 2 dB the noise is high-frequency (H-type), 2 to 7 dB is medium (M-type), and greater than 7 dB is low-frequency (L-type). The appropriate H, M, or L attenuation value from the HPD datasheet is then applied. This gives more accurate protection estimates than the single-number NRR or SNR approach.

Second, engineering noise control design requires knowing which frequency bands dominate the source so that control measures (enclosures, damping, silencers) can be tuned to the right frequencies.

Third, low-frequency noise complaints (below 250 Hz) are poorly described by dB(A) and often require the raw or C-weighted octave band data to assess properly.

Enter WBGT directly if you have an instrument that measures and reports WBGT directly. The instrument's globe thermometer captures the solar radiation load, so no further correction is needed.

Measured temperatures (Tnwb + Tg + Tdb) if you have a psychrometric wet bulb, globe, and dry bulb thermometer separately. The tool applies the ACGIH formula to compute WBGT from those components, using the indoor/shade or outdoor/sun formula as selected.

Estimate from met data if you have no on-site instruments and only standard meteorological data (dry bulb temperature, relative humidity, wind speed). The tool estimates the psychrometric wet bulb and, for outdoor sun conditions, computes globe temperature using a sphere energy balance model (Liljegren 2008) with clear-sky solar irradiance. Measured instruments are always preferred; this mode is for planning or retrospective assessment.

They should not differ — the tool uses ACGIH Table 3 as the primary TLV source for both acclimatised and unacclimatised workers. The TLV card shows the Table 3 threshold for the selected work allocation, metabolic rate, and acclimatisation status. The Action Limit is derived separately from the ACGIH formula (AL = 60.0 − 14.1 × log₁₀M) and capped at the TLV.

If you see a discrepancy, check that the work allocation and metabolic rate dropdowns match what you intended. The highlighted cell in the Table 3 grid shows your current selection.

A Similar Exposure Group is a group of workers whose exposures are similar enough in source, path, and duration that a sample from part of the group can be used to characterise the whole group's exposure distribution. The concept is central to the AIHA exposure assessment framework.

Defining SEGs correctly, before sampling, is the most important step in any exposure assessment program. The Exposure Profiler analyses data at the SEG level and assumes the data you enter represents a valid SEG.

Both methods estimate the same underlying lognormal exposure distribution, but they handle uncertainty differently.

The frequentist method (maximum likelihood estimation) gives point estimates of the geometric mean and geometric standard deviation. It is straightforward but provides no direct measure of uncertainty in those estimates.

The Bayesian method incorporates prior information about plausible industrial hygiene exposure distributions and produces full credible intervals on the parameters. This is particularly useful when sample sizes are small (fewer than six samples), where frequentist point estimates can be highly unstable.

The AIHA IHSTAT methodology recommends the Bayesian approach as default, especially for small datasets. The Exposure Profiler runs both and presents both sets of results.

The exceedance fraction is the estimated proportion of the SEG's daily exposures that exceed the OEL, expressed as a percentage. A result of 5% means an estimated 5 in 100 working days would produce an exposure above the limit.

The AIHA risk band classification uses the 95th percentile credible interval of the exceedance fraction (not the point estimate) to assign the SEG to a risk band from 0 (clearly acceptable) to 4 (clearly unacceptable). Using the upper confidence bound rather than the point estimate makes the classification conservative, which is appropriate given the consequences of under-estimating exposure risk.

The tool implements the simple health risk assessment framework from IOGP Report 384 (Occupational Health Management in the Oil and Gas Industry). It combines two independent ratings for each workplace hazard to produce a risk level that determines the urgency of control action.

The first rating is the exposure band (E1 to E4), which describes how large the exposure is relative to the applicable occupational exposure limit or reference level. You can set this quantitatively — by entering a measured or estimated concentration and the reference level, from which the tool calculates the ratio — or qualitatively, by selecting the band that best describes the exposure scenario. E1 is rarely exposed (estimated below 10% of the reference level) through to E4, where exposure is at or above the reference level.

The second rating is the health consequence severity (S1 to S4), which describes how serious the potential health outcome is if the hazard is realised. S1 is negligible (transient, self-limiting effects) through to S4 (potentially fatal or permanently disabling).

The risk level is the product of the two numeric scores: 1–2 is Low, 3–6 is Medium, 8–12 is High, and 16 is Very High. Each level carries a required action and a target timeframe — from routine monitoring at Low through to immediate work stoppage at Very High. The tool plots all rated hazards on the 4x4 risk matrix and produces a prioritised action plan sorted by risk level.

The tool is designed for use by occupational hygienists and health and safety practitioners. It is a screening and prioritisation aid, not a substitute for quantitative exposure measurement or full health risk assessment by a qualified professional.

Control Banding is a qualitative risk assessment method used when quantitative exposure data is unavailable or impractical to obtain. The tool classifies a substance into a hazard band based on its health hazard classification and volatility or dustiness, then assigns a control approach (ranging from general ventilation to engineering containment or specialist advice) based on the estimated exposure potential.

The output is a recommended control category, not a measured or modelled concentration. It is appropriate for prioritising controls or screening substances before quantitative assessment, not as a substitute for measurement-based compliance assessment.

The tool combines individual uncertainty components (sampling pump flow rate, sampling volume, analytical recovery, method precision, and others) using the ISO GUM (Guide to the Expression of Uncertainty in Measurement) framework. Each component is expressed as a standard uncertainty, then combined in quadrature to give the combined standard uncertainty. Multiplying by a coverage factor k gives the expanded uncertainty at the chosen confidence level.

The result is expressed as a percentage of the measured value. This can be used to assess whether the uncertainty band around a measurement crosses a regulatory limit, which affects the compliance decision.

The classifier uses the WHO Laboratory Biosafety Manual (4th edition, 2020) risk group framework, which categorises microorganisms into four risk groups based on pathogenicity, transmissibility, host range, availability of effective prophylaxis or treatment, and route of exposure. The tool maps risk group to containment level and flags relevant precautions.

Classification outputs are for planning and guidance purposes. Formal biological risk assessment requires a qualified biosafety professional and must account for site-specific factors not captured by the risk group alone.

The tool estimates the per-pathogen seroconversion probability (per 1,000 exposures) for HIV, HBV, and HCV following an occupational exposure incident, then provides post-exposure prophylaxis (PEP) guidance based on the inputs entered. Inputs include the exposure route (percutaneous hollow needle, solid sharp, mucosal splash, or non-intact skin), the source material type, the elapsed time since exposure, the source patient's known or suspected status for each pathogen, and the healthcare worker's HBV vaccination and antibody status.

Transmission probabilities are derived from CDC surveillance data (2005 Updated US Public Health Service Guidelines) and are modified by route, source status, and vaccination status. The tool outputs a per-pathogen risk estimate, an urgency classification, and specific PEP recommendations — including standard regimens for HIV PEP, HBIG and vaccination protocols for HBV, and monitoring guidance for HCV (for which no effective PEP exists).

The tool does not replace clinical assessment. Any occupational exposure to blood or potentially infectious material requires immediate medical review regardless of the estimated risk level.

The tool implements the IICRC S520 Standard and Reference Guide for Professional Mold Remediation (3rd edition) for contamination condition classification (Conditions 1, 2, and 3) and worker protection levels (Levels I–IV). EPA remediation scope thresholds are drawn from EPA 402-K-01-001 (Mold Remediation in Schools and Commercial Buildings), which defines area-based scope categories (small: under 1 ft², small-medium: 1–10 ft², medium: 10–100 ft², and large: over 100 ft²).

The tool classifies visible contamination extent, material porosity, moisture source status, spatial distribution, and optional air sampling data (indoor-to-outdoor Aspergillus/Penicillium ratio and presence of atypical indoor species) to determine contamination condition, required containment, and appropriate remediation scope. Outputs are guidance-level determinations; formal mould assessments require a qualified assessor and site-specific professional judgment.

A PID (photoionization detector) is a direct-reading instrument that measures volatile organic compound (VOC) concentrations in air by ionising gas molecules with a UV lamp and measuring the resulting ion current. PIDs are fast, sensitive, and widely used for screening, leak detection, and short-term exposure assessment.

PIDs are calibrated to a reference gas — almost universally isobutylene — at a defined concentration, giving isobutylene a correction factor (CF) of 1.00. Every other compound responds differently depending on its ionization energy (IE) and molecular structure, so a CF is required to convert the raw PID reading to the true concentration of the target compound: true concentration = PID reading × CF. A CF greater than 1.00 means the instrument over-reads for that compound relative to isobutylene; a CF less than 1.00 means it under-reads.

Some manufacturers use the term response factor (RF) for the same concept — the PID Correction Factor tool covers both, and the lookup confirms which convention each manufacturer uses.

NR (No Response) means the compound's ionization energy (IE) equals or exceeds the UV lamp energy, so the lamp cannot ionise the compound and the instrument produces no meaningful signal. For example, methane has an IE of 12.6 eV and does not respond on a standard 10.6 eV lamp.

IE values and lamp energies are both expressed in electron volts (eV). The three common lamp energies are 9.8 eV, 10.6 eV (most common), and 11.7 eV. A compound that shows NR on a 10.6 eV lamp may respond on an 11.7 eV lamp if its IE falls between the two values. The PID Correction Factor tool shows CF values per lamp energy and flags NR where applicable.

CF values are determined empirically by each manufacturer using their specific instrument design, lamp, detector geometry, and calibration procedure. Differences in lamp output stability, ionisation chamber volume, and signal processing all contribute to inter-instrument variation. CFs for the same compound can legitimately differ by 10–30% between manufacturers; larger discrepancies usually indicate a data entry error in one of the source documents or a measurement at a different lamp energy.

Always use the CF from the manufacturer's datasheet for your specific instrument and lamp. Do not substitute another manufacturer's CF without verification.

Ototoxic chemicals are substances — including certain organic solvents (toluene, styrene, xylene), heavy metals (lead, mercury), and asphyxiants (carbon monoxide) — that can independently damage the cochlea and auditory nerve. Research shows that combined noise and ototoxic chemical exposure causes greater hearing damage than either alone. When the Noise Assessment Suite detects ototoxic co-exposure, it flags this so users know that normal noise action levels may be insufficient and that lower intervention thresholds or enhanced hearing protection should be considered.

WBGT (Wet Bulb Globe Temperature) is a simple environmental index used for initial screening. It accounts for radiant heat, humidity, and air temperature but not individual physiology or actual work demands. TWL (Thermal Work Limit) is a rational index that calculates the maximum sustainable work rate for a given set of environmental conditions — factoring in air temperature, humidity, radiant heat, and wind speed. The AIOH (2025) recommends WBGT for initial screening and TWL or PHS (ISO 7933:2023) when screening thresholds are exceeded or for ongoing site management.

Tool 2: Dilution Ventilation shows the time it takes for airborne concentration to build up from a clean room start to 90% and 99% of the steady-state target concentration (which equals the OEL or target you entered), assuming constant generation rate G and the required ventilation flow Q.

The formula is derived from the first-order differential equation for a well-mixed room: C(t) = C_ss × (1 − e^−Qt/V), where V is the room volume, Q is the required flow rate, and C_ss is the steady-state concentration. Time to 90% of steady state is 2.30 × V/Q; time to 99% is 4.61 × V/Q. The room volume must be entered for this output to appear.

This is useful for understanding how quickly an empty room reaches a hazardous concentration after a process starts — for instance, how long workers have before returning to a space where a solvent process is running.

Tool 3: Local Exhaust Ventilation uses the standard ACGIH equations from Industrial Ventilation: A Manual of Recommended Practice. For plain (unflanged) hoods: Q = Vc x (10X2 + A). For flanged hoods: Q = 0.75 x Vc x (10X2 + A) — the flange reduces required airflow by approximately 25% by blocking the rear hemisphere of induced air. For slot hoods: Q = 3.7 x Vc x L x X (plain) or 2.8 x Vc x L x X (flanged). For canopy hoods above a buoyant source: Q = 1.4 x P x H x Vc.

Use Tool 1: Generation Rate in the Ventilation Suite. Enter how much liquid is consumed or evaporated during the process (in mL, L, g, or kg) and over what duration. The tool converts this to a generation rate in mg/s using the substance's specific gravity and the fraction that evaporates. For spray operations, assume 100% evaporation. For dip tanks or immersion processes, a smaller fraction typically becomes airborne.

The two-zone near-field/far-field (NF/FF) model is for indoor workplaces. It divides the room into two zones: a near-field zone (small volume directly around the source or worker) and a far-field zone (the remainder of the room). The near-field concentration is always higher than the far-field because contaminant transport between zones is limited by turbulent mixing, captured by the inter-zone mixing rate (β). This model is appropriate for estimating worker exposure close to a source — for example, a solvent cleaning operation in a ventilated room.

The Gaussian plume model is for outdoor releases from stacks or fugitive sources. It models how a plume spreads downwind in two dimensions (horizontal and vertical) under defined meteorological conditions, and estimates the ground-level concentration at specified distances. The key inputs are the emission rate, effective stack height, wind speed, and atmospheric stability class.

The two models are suited to completely different scenarios and should not be confused. For indoor near-source exposures, use NF/FF. For stack or fugitive outdoor releases, use the Gaussian plume.

Stability class describes how turbulent the atmosphere is, which determines how rapidly the plume disperses. Class A (very unstable) produces wide, rapidly dispersing plumes and is associated with strong solar radiation and light winds — typically a clear, hot afternoon. Class F (stable) produces narrow, slowly dispersing plumes and is associated with clear nights with light winds, when the ground cools rapidly and surface-layer turbulence is suppressed.

The stability class guide table in the tool shows the Pasquill (1961) classification matrix, which cross-references surface wind speed with solar radiation intensity and cloud cover. Class D (neutral) applies under overcast skies at any wind speed, or for wind speeds above about 6 m/s regardless of sky condition.

For worst-case occupational or community exposure assessments, Class F (or occasionally E) with low wind speed typically produces the highest ground-level concentrations at intermediate distances. Class A produces the highest concentrations very close to a ground-level source, because plume rise is less effective but dispersion is rapid. Always check the model across several stability classes when assessing receptor impact.

β (m³/s) represents the turbulent air exchange rate between the near-field and far-field zones. It is not the same as the room ventilation rate Q, which is the supply of fresh air from the ventilation system. β captures how quickly contaminant mixes across the boundary between the near-source zone and the rest of the room.

A default of 0.1 m³/s is commonly used for light industrial indoor environments with minimal air movement. For processes that generate significant air movement (grinding, spray operations, strong convective currents from heat sources), values of 0.3 to 0.5 m³/s are more appropriate. A very low β (e.g. 0.02 m³/s) represents stagnant air close to the source, which produces very high near-field concentrations. The model is most sensitive to β when β is small relative to Q.

The Gaussian plume model assumes flat terrain, steady-state meteorological conditions, a uniform wind field, and a continuous point source. It is not valid for calm wind conditions (wind speed below about 1 m/s), complex terrain (hills, valleys, buildings causing significant flow distortion), building downwash, time-varying emissions, or very short distances from the source (less than 50 m).

The model also represents a single meteorological snapshot. In practice, meteorological conditions vary continuously, so Gaussian plume results represent conditions at a specific moment — not a time-averaged or worst-case annual estimate. For regulatory air quality impact assessment, sector-averaged or annual meteorological data and a regulatory-grade model (such as AERMOD or AUSPLUME) are required. The Exactus Labs Dispersion Model is appropriate for rapid screening, occupational exposure estimation, and understanding the order-of-magnitude impact of changes to source parameters.

Uncertainty in Gaussian plume predictions is typically a factor of 2 to 5 under real conditions, which is inherent to the model and the variability of atmospheric turbulence. This uncertainty should be considered when comparing model outputs to regulatory limits.

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The suite currently covers 20 tools across Physical Agents, Chemical Agents, Biological Agents, and Risk Assessment & Analytics. Future additions are evaluated based on practitioner demand and whether the underlying methodology is sufficiently well-defined to implement reliably.

The tools directory shows everything currently available.

Yes. Email [email protected] with a description of the calculation you need, the standard it should implement, and why existing solutions fall short. Priority is based on breadth of practitioner need and whether the calculation is well-defined enough to implement without ambiguity.

Email [email protected] with the tool name, the inputs you used, the result you got, what you expected, and the standard clause you are referencing. Accuracy reports are treated seriously and investigated promptly. If the tool is wrong, it gets corrected and the change is noted.