Workplace Regulations 1992 regulation 6, UK wide
Indoor Air Quality and Ventilation Assessments
Complaints about stuffy rooms, headaches and afternoon fatigue are usually treated as a facilities grumble rather than a health and safety matter. They are a ventilation question with a legal duty behind them. AL23 Safety measures how your building actually performs against regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992 and sets out what to change, for clients UK wide.
What is an indoor air quality assessment?
Measuring how the building performs when it is full, not when it is empty
An indoor air quality assessment logs the conditions occupants are exposed to across a full occupied cycle, then reads them against the duty in regulation 6, against recognised comfort criteria and against what the ventilation was designed to do. It pairs instrument data with a physical survey of the plant supposed to be delivering the air.
The honest starting point is that most indoor air parameters have no UK workplace limit value. There is no statutory list of what to measure and no legal pass mark for carbon dioxide, particulate or volatile organic compounds in an ordinary office. The output is a comparison against guideline values and against design intent, not a pass or fail against law. Anybody presenting an office air test as a compliance certificate is overselling it.
Where the air contains a substance hazardous to health the position changes. The Control of Substances Hazardous to Health Regulations 2002 take over and general ventilation stops being the relevant control. Process air is dealt with through the COSHH assessment and through extraction rather than through the air handling system.
Who needs one
The triggers that bring us in
- Persistent complaints of stuffiness, headaches, tiredness or eye and throat irritation that improve away from the building
- Sealed or deep plan floorplates where windows do not open and the mechanical system is the only source of fresh air
- Meeting rooms and teaching spaces used at high occupancy for long periods, which is where carbon dioxide climbs fastest
- Recently refurbished space, where new furniture, adhesives and engineered timber are still off-gassing
- Premises next to a loading bay, a car park, a plant room or a busy road, where the intake may be drawing in the problem
- Sites where mechanical ventilation plant has no working device to warn of failure, which regulation 6 requires where health or safety depends on it
- Disputes with a landlord or tenant where somebody needs data rather than competing opinions
The regulations that apply
Your legal framework, in plain terms
The duty sits in regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992, supported by the Approved Code of Practice L24. Above it is the general duty in the Health and Safety at Work etc. Act 1974 and the assessment duty in the Management of Health and Safety at Work Regulations 1999. Below it sit HSE's ventilation guidance and the CIBSE design material, which do most of the real work. Only the first of those is law.
Workplace (Health, Safety and Welfare) Regulations 1992, regulation 6
Every enclosed workplace must be ventilated by a sufficient quantity of fresh or purified air. Regulation 6 also requires mechanical ventilation plant to be fitted with a device giving visible or audible warning of failure where that is necessary for health or safety.
HSE ventilation guidance
The fresh air supply rate should not normally fall below 5 to 8 litres per second per occupant. HSE notes that 10 litres per second per person is recommended in some building guides as suitable for most commercial buildings, attributing that higher figure to those guides rather than adopting it as its own floor.
COSHH 2002
Where the airborne contaminant is a substance hazardous to health, COSHH is the operative duty. General ventilation is not a COSHH control measure.
CIBSE TM40, Health and wellbeing in building services, March 2020
Deliberately non-prescriptive on indoor air quality. Where UK regulation is silent it directs practitioners to internationally recognised health based guidelines, particularly those from the World Health Organization. It rests on source control and the precautionary principle.
CIBSE Guide A, Environmental Design, eighth edition, 2015
The standard UK source for thermal comfort criteria, internal design conditions and outdoor air supply calculation. It remains the current edition as at August 2026.
Schools sit slightly apart. Building Bulletin 101, Guidelines on ventilation, thermal comfort and indoor air quality in schools, last updated by the Department for Education in August 2018, is guidance rather than law. Compliance is contractually required on Department for Education funded projects and it supports Building Regulations Part F compliance for schools.
What we assess
What the instruments read and the plant reveals
Carbon dioxide
, logged continuously through occupied hours with a non-dispersive infrared instrument, recorded alongside actual occupancy so the data can be interpreted
Dry bulb temperature and relative humidity
, against the HSG132 reference figures of around 19 °C in a normal office with a 16 °C minimum, plus relative humidity of 40 to 70 per cent
Air velocity at occupant level
, for draught risk at desks near diffusers and doors, against the HSG132 range of 0.1 to 0.15 m/s normally and up to 0.25 m/s in summer
Particulate matter at PM2.5 and PM10
, against World Health Organization guideline values because no UK workplace figure exists
Total volatile organic compounds
as a screening indicator, with speciation by diffusive sampling to MDHS 88 where the screen flags something
Carbon monoxide
wherever there is combustion plant, a loading bay or an adjacent car park
Fresh air supply rate per occupant
, measured or calculated against the 5 to 8 litres per second floor
The ventilation system itself
, covering intake location, recirculation, filter grade and condition, balance, controls and the plant failure warning device
Job design factors
, covering routine work, poor control over the local environment and prolonged screen use
Our process
Logged across a full occupied week, then interpreted
- 01
Scoping and complaint review
We take the symptom pattern, the floor plan and the occupancy first. Where the complaints cluster tells us where to put the instruments.
- 02
Logging
Monitors sit at head height, at least 50 cm away from people so exhaled breath does not give falsely high readings, well away from windows, doors and air supply openings. Larger spaces get multiple positions and multiple instruments. Logging runs throughout occupied periods rather than as snapshot readings.
- 03
Plant and fabric survey
We inspect the air handling units, intakes, terminals, filters and controls, checking them against the original design intent and commissioning data where that exists.
- 04
Interpretation
Data is read against the regulation 6 duty, HSE's supply rate figures, the HSG132 comfort ranges and the guideline values for each parameter.
- 05
Report and action plan
We separate the changes that cost nothing from those that need a capital scheme. The plan sets out what to fix, in what order and who owns it.
What you get
Logged data plotted against occupancy, not spot readings
- An indoor air quality report plotting logged data against occupancy for each monitored space, not a table of spot readings
- A statement of fresh air supply rate per occupant for each space, compared against the 5 to 8 litres per second figure
- A ventilation condition report covering intake, filtration, recirculation, controls and failure warning provision
- A prioritised action plan splitting operational fixes, maintenance fixes and capital works, with target dates
- Clear labelling of which findings relate to a legal duty and which relate to comfort or guideline values
What we need from you
Plans, plant records and honest occupancy patterns
- Floor plans with room names, design occupancy and actual occupancy patterns
- Any commissioning data, schematics, maintenance records and filter change logs you hold
- A summary of the complaints received, including who reported what and where they sit
- Access to plant rooms, ceiling voids and roof mounted equipment, with permit requirements confirmed in advance
Why AL23 Safety
Honest about what is law and what is comfort
Accountable
If the honest finding is that the building is adequately ventilated and the problem is workload, layout or temperature control, that is what the report will say.
Data over reassurance
We log across occupied periods against recorded occupancy. A single reading taken at nine in the morning in an empty meeting room proves nothing.
Clear about what is law and what is not
Regulation 6 is a duty. Guideline values are not. We label every finding so you know which is which.
UK wide
We assess offices, schools, laboratories, warehouses and healthcare premises for clients across the UK from our Manchester base.
Talk to us about your building
Objective data instead of an argument about the windows
If people are complaining and the facilities team says the system is fine, a week of logged data usually settles it. Describe the building on a call and we will tell you what we would measure.
Common questions
Answers, up front
Cannot see your question? Get in touch and we will answer it directly.
Contact usHSE treats carbon dioxide readings consistently above 1500 ppm in an occupied room as an indicator of poor ventilation requiring action. Readings consistently below around 800 ppm are generally taken to indicate a well ventilated space, a figure that entered wide use through pandemic-era guidance rather than through the current HSE ventilation pages. HSE also gives 1000 ppm as roughly equivalent to 10 litres per second per person, which is the conversion that makes the reading useful.
No. HSE is explicit that carbon dioxide measurements are only a broad guide to ventilation rather than demonstrating safe levels. Carbon dioxide tells you how much of the air people are re-breathing. It says nothing about particulate, solvent vapour or combustion products drawn in from outside.
Cost is driven by the number of spaces, the logging period, how many parameters are measured and whether laboratory analysis is needed for volatile organic compound speciation. A single open plan floor logged for carbon dioxide, temperature and humidity is a modest exercise. A multi-storey building with a full plant survey and speciated sampling is a project. Tell us the building and the symptoms and we will scope it.
Logging normally runs across a full working week so the data captures Monday and Friday occupancy as well as the busy midweek days. The plant survey is usually a single day. The report follows within an agreed period after the loggers come down.
Yes. HSG132 defines it as a phenomenon where symptoms increase with time spent in a building and improve or disappear away from it. That building relatedness is the diagnostic feature. HSG132 dates from 2000 and predates the carbon dioxide proxy approach entirely. It carries no carbon dioxide parameter and its ventilation figures have been overtaken. Its lasting value is the insistence that job factors, routine work and lack of individual control over the environment sit alongside the physical causes. We treat both, which is why we often pair this work with DSE assessments.
Regulation 6 applies to every enclosed workplace, which makes the answer yes. Office air is rarely a substance hazardous to health question, which is why we keep it separate from the COSHH work. The practical issues in office environments are occupancy density, recirculation, temperature control and plant that has drifted from its commissioned settings.
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