Dilution Ventilation Flow
Calculate the airflow needed to dilute a contaminant, Q = (G × K) ÷ C, from the contaminant generation rate G, a safety/mixing factor K and the allowable limit concentration C. The result, in the consistent flow unit, is the volume of clean air that must be supplied/exhausted to keep the contaminant concentration below the tolerance limit in the breathing zone. General dilution ventilation suits low-toxicity, diffusely generated contaminants; the K factor corrects for imperfect air mixing. Enter the generation rate, the safety factor and the limit concentration.
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Dilution ventilation flow
A general dilution ventilation system controls airborne contaminants by mixing the contaminated air with large volumes of clean air, lowering the concentration to safe levels. The required airflow is Q = (G × K) ÷ C, where G is the contaminant generation rate (mass per time), C is the allowable limit concentration (the exposure limit below which exposure is safe), and K is a safety and mixing factor (typically 3 to 10) correcting for the fact that air never mixes perfectly — there are dead zones, and the worker may be near the source, where the concentration is higher than the average. The logic is direct: the more contaminant generated, the larger the airflow; the lower the tolerable limit (a more toxic substance), the larger the airflow. Dilution suits contaminants of low toxicity, generated in a diffuse manner (not concentrated at one point) and at a uniform rate — such as low-concentration solvent vapors or heat. For toxic contaminants or those generated at well-defined points, it is inadequate (it would demand enormous airflows and still expose whoever stands near the source): those cases call for local exhaust ventilation, which captures the contaminant at the origin. Enter the generation rate, the safety factor, and the limit concentration.
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Noise Dose
Calculate the occupational noise dose, D = (C ÷ T) × 100%, dividing the effective exposure time C by the maximum allowed time T for the measured noise level and multiplying by 100. The result, in %, shows how much of the maximum daily exposure the worker accumulated: 100% is the tolerance limit (85 dB(A) for 8 hours, with a 5 dB exchange rate in Brazil). Doses above 100% require controls and indicate risk of noise-induced hearing loss. For several levels, the C/T terms are summed. Enter the exposure time and the maximum allowed time.
Maximum Noise Exposure Time
Calculate the maximum daily allowed noise exposure time, T = 8 ÷ 2^((SPL − 85) ÷ 5), from the sound pressure level SPL (dB(A)). The result, in hours, is the maximum exposure duration before reaching a 100% dose under the Brazilian NR-15 (85 dB(A) limit for 8 h, with a 5 dB dose-doubling rate). Every 5 dB above 85 halves the allowed time: 90 dB(A) allows 4 h, 95 dB(A) only 2 h. It is the basis for dose calculation and the planning of rotation and breaks. Enter the sound pressure level.
Normalized Exposure Level (NEN)
Calculate the 8-hour normalized exposure level (NEN), NEN = NE + 10·log₁₀(t ÷ 480), from the measured exposure level NE (dB(A)) and the actual exposure time t (minutes). The result, in dB(A), converts an exposure of any duration into the equivalent level that would produce the same dose over a standard 8-hour (480 min) shift, allowing direct comparison with the tolerance limit and action level. It is the quantity used by occupational hygiene standards to assess continuous or intermittent noise. Enter the measured level and the exposure time.
Capture Flow (Local Exhaust)
Calculate the capture flow of an unflanged local exhaust hood, Q = V·(10·X² + A), from the capture velocity V (m/s), the source-to-hood distance X (m) and the hood face area A (m²). The result, in m³/s, is the flow needed for contaminated air to be drawn into the hood with enough velocity to overcome air currents and the contaminant's inertia. The Della Valle/ACGIH equation shows the flow grows with the square of distance — hoods should be as close to the source as possible. It is the basis of local exhaust ventilation design. Enter the capture velocity, the distance and the hood area.
Mold Fill Time
Calculate the fill time of a casting mold, t = V ÷ Q, dividing the cavity volume V by the metal flow rate Q of the gating system. The result, in seconds, is the time to completely fill the mold with molten metal. It is a critical parameter: filling too slowly lets the metal cool and solidify before filling everything (cold shut, misrun defects), while too fast causes turbulence, gas entrapment, mold erosion and inclusions. The optimal time depends on the part's weight and thickness and the metal. Sizing the gating system for the right time is central to casting design. Enter the cavity volume and the flow rate.
Weld Dilution
Compute a weld's dilution, D = (melted base-metal area / total bead area)·100%, the proportion of the bead that came from the base metal rather than the filler. It is crucial in cladding and dissimilar-metal joints: high dilution mixes in more base metal, altering the bead's composition and properties (anti-corrosion cladding aims for low dilution). Enter the melted base-metal area and the total bead area.
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