ToolsAsbestosAir Sampling

Number of Pumps Calculator (Stage 3)

Calculate how many air sampling pumps you need for Stage 3 of a 4-stage asbestos clearance. HSG248 formula based on enclosure size.

Last updated 3 March 2026

About this tool

Calculate the number of air sampling pumps required for Stage 3 of a 4-stage asbestos clearance procedure. The number of samples is calculated using the clearance pump indicator formula from HSG248. Simply enter the enclosure dimensions and get your answer — no more looking up tables on site.

How to use

Enter the enclosure length, width, and height in metres. For enclosures under 10 m³, only 1 air test is required. For larger enclosures, the tool calculates the number of pumps using the formula ³√A - 1 (always rounded down), where A is the floor area for enclosures ≤3m high, or the volume divided by 3 for enclosures >3m high.

Pass criteria

For the Stage 3 clearance to pass, at least 80% of air sample results must be below 0.010 f/ml, and ALL results must be below 0.015 f/ml. If any single result exceeds 0.015 f/ml, or more than 20% exceed 0.010 f/ml, the clearance fails and the enclosure must be re-cleaned before re-testing.

Reference

HSG248 — Asbestos: The analysts' guide for sampling, analysis and clearance procedures (HSE, 2021). The number of air tests is calculated using the clearance pump indicator formula: Pumps = ³√A - 1 (always rounded down). For enclosures <3m high, A is the floor area in m². For enclosures >3m high, A is the volume in m³ divided by 3. Enclosures under 10 m³ require 1 air test.

Revision history

3 March 2026: Initial release.

Disclaimer

This tool is provided for educational and general information purposes only. It is not a substitute for professional engineering advice, design or verification.

Diggy and its contributors are not licensed engineering consultants and no results generated by this tool should be used directly for construction, design or safety-critical decisions.

All values and outputs are based on published empirical correlations and should be independently checked and confirmed by a qualified geotechnical engineer before use.

By using this tool, you accept full responsibility for how you interpret and apply the information provided.

Spotted an error? Let us know.

Enclosure length (m)

Enclosure width (m)

Enclosure height (m)