HSE LEV Calculations – Useful Online Calculator for LEV Assessors

LEVCentral Expert Commentary

Every LEV engineer performs calculations on a regular basis. Whether determining duct volume flow, calculating air changes, converting pressure units or averaging face velocity readings, these calculations are fundamental to commissioning, troubleshooting and Thorough Examination & Testing (TExT).

To assist practitioners, HSE provides a free online LEV Calculator containing a range of simple engineering calculators commonly used during LEV surveys. Rather than replacing engineering knowledge or design calculations, the tool provides a quick and convenient way of checking measurements and carrying out routine calculations in the field.

The calculator includes functions for:

Unit conversions
Averaging multiple velocity readings
Volume flow calculations
Air change rate calculations
Air density calculations
Air velocity calculations using Pitot tube measurements
Conversion between ppm, mg/m³ and vapour pressure for gases and vapours.

For LEV engineers carrying out commissioning or statutory Thorough Examination & Testing, these are among the calculations performed most frequently. Having them available within a single web page makes the calculator a useful reference during site work.

It is important, however, to recognise the calculator’s limitations. It performs individual engineering calculations but does not design LEV systems. Successful ventilation design still requires an understanding of contaminant behaviour, hood design, duct sizing, transport velocities, pressure losses, fan performance and system balancing—subjects covered in publications such as HSG258 and the ACGIH Industrial Ventilation Manual.

View HSE LEV Calculator

Open the HSE LEV Calculator

What the Calculator Includes

The HSE calculator provides quick access to:

Engineering unit conversions
- Inches and metres
- Pascals, mm water gauge and inches water gauge
- Cubic feet and cubic metres
- Feet/minute and metres/second
Average velocity calculator
- Average multiple face velocity readings
- Display acceptable ±20% range
- Identify variation across hoods
Volume flow calculator
- Circular ducts
- Rectangular ducts
- Booth openings and fume cupboard faces
Air change rate calculator
- Room volume
- Extract rate
- Air changes per hour (ACH)
Air density calculator
- Temperature correction
- Atmospheric pressure correction
Pitot tube air velocity calculator
- Velocity from total and static pressure measurements
Gas concentration conversions
- ppm
- mg/m³
- Vapour pressure conversions.

Source Information

Organisation: Health and Safety Executive (HSE)

Resource: LEV Calculations – Useful Calculator for LEV Assessors

Resource Type: Free Online Engineering Calculator

Primary Topics: Airflow Calculations, Volume Flow, Air Velocity, Pitot Tubes, Air Changes, LEV Commissioning

Audience: LEV Designers, Commissioning Engineers, LEV Test Engineers, Occupational Hygienists, Mechanical Engineers and Students.

LEVCentral Perspective

This calculator is an excellent field aid, particularly for engineers carrying out commissioning or TExT work. It reduces the need for manual calculations and provides a quick way of checking measurements while working on site.

However, it should not be viewed as a ventilation design package. It answers questions such as:

“What is the volume flow through this duct?”
“What is the average of these face velocity readings?”
“What air velocity does this Pitot pressure represent?”

It does not answer more fundamental engineering questions such as:

Is this the correct hood design?
Is the capture velocity adequate?
Is the duct correctly sized?
Will the fan operate on the correct part of its performance curve?
Will this system provide adequate contaminant control?

These decisions still depend upon engineering judgement and a sound understanding of LEV design principles.

Further Resources

Recommended Learning

Thought Leadership

Engineering calculators are valuable tools because they reduce the time spent performing repetitive calculations and minimise the risk of arithmetic errors. However, they should never replace engineering understanding.

A calculator can determine the airflow through a duct in seconds, but it cannot determine whether that airflow is sufficient to capture a hazardous contaminant. Likewise, it can calculate air changes per hour, but it cannot judge whether general ventilation is an appropriate control measure in place of Local Exhaust Ventilation.

Competent LEV practitioners use calculators to support their work—not to make engineering decisions for them. The HSE LEV Calculator is therefore best viewed as a practical companion for field measurements, sitting alongside the knowledge contained in HSG258 and the ACGIH Industrial Ventilation Manual, rather than replacing either of them.