Indoor Air Quality at Work: An Employer's Guide

What does the law actually require?

Employers' obligations for workplace ventilation come from Regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992, which requires that every enclosed workplace is ventilated by a sufficient quantity of fresh or purified air. The Approved Code of Practice (ACOP) accompanying the Regulations expands on this, noting that ventilation should be sufficient to remove and dilute warm, stale air and replace it with fresh air, and that any mechanical ventilation system should be regularly maintained and kept in good working order.

Notably, the law does not set a single numerical standard, such as a fixed carbon dioxide level or a required number of air changes per hour, that every workplace must meet. Instead, the duty is framed around the general requirement that the air is adequate for the number of people and the nature of the work being carried out. This makes the regulation easy to satisfy on paper and surprisingly easy to fail in practice, since "sufficient" ventilation in a half-empty office looks very different from "sufficient" ventilation in the same room at full occupancy.

Employers also carry a broader duty under the Health and Safety at Work etc. Act 1974 and the Management of Health and Safety at Work Regulations 1999 to assess and control workplace risks generally, which includes air quality where it could reasonably affect employee health.

Why ventilation gets overlooked

Ventilation rarely fails all at once. It degrades gradually, as HVAC filters clog, as buildings are repartitioned without adjusting airflow, as more desks are added to a room designed for fewer occupants, or as windows that once opened are sealed for security or energy efficiency reasons. None of these changes typically trigger a formal review, because there is no equivalent of a fire alarm test or a PAT testing schedule that forces the issue back onto someone's desk.

It also tends to sit in a grey area of responsibility. Facilities teams may assume building services contractors are monitoring air quality as part of routine HVAC maintenance, while HR and health and safety leads may assume that if there were a real problem, staff would say so clearly enough to prompt action. In practice, both assumptions often turn out to be wrong, and ventilation ends up being one of the more common gaps found when reviewing a client's wider compliance position.

Common signs of poor indoor air quality

Some warning signs are physical and easy to spot: persistent stuffiness or stale odours, condensation on windows in cold weather, visible mould growth around windows or in poorly ventilated corners, or dust accumulating unusually quickly around vents and desks.

Others show up in how people feel and perform rather than in the building itself. Headaches, drowsiness and difficulty concentrating later in the day, particularly in meeting rooms or densely occupied areas, are classic symptoms of elevated carbon dioxide from insufficient fresh air exchange. Complaints of dry eyes, irritated throats, or a general sense that a particular room "feels heavy" are also common, and are worth taking seriously even when they seem minor individually. A noticeable rise in short-term sickness absence concentrated in one part of a building, rather than spread evenly, can likewise point back to an air quality issue rather than coincidence.

How to monitor and improve air quality

The starting point for most employers is simple monitoring rather than a major capital project. Portable or desktop carbon dioxide monitors are inexpensive and give a reasonable proxy for ventilation adequacy, since CO2 concentration rises predictably as fresh air supply falls behind occupancy. CIBSE and other industry guidance commonly treat concentrations climbing well above outdoor background levels as a signal to investigate further, though this is a practical benchmark rather than a legal limit in most office settings.

Beyond monitoring, the improvements available generally fall into three categories. Building-level changes include servicing and rebalancing HVAC systems, replacing filters on schedule, and checking that ductwork hasn't been blocked or reconfigured by unrelated works. Behavioural changes include making better use of openable windows where available, and reviewing whether meeting rooms are being booked for more people than their ventilation was designed to support. Source control means reducing what is being emitted into the air in the first place, from printer and copier placement to the choice of cleaning products used overnight.

For any of these steps to be worthwhile, they need to be based on an actual assessment of the building rather than assumptions carried over from when it was first fitted out.

Building air quality into your wider compliance picture

Indoor air quality is easiest to manage well when it isn't treated as an isolated concern that only gets attention after a complaint. It sits alongside the same building fabric, plant and maintenance regimes that govern legionella and water hygiene risk, asbestos management, and general workplace health and safety, and a weakness in one area is often a useful early indicator that others deserve a closer look too. Employers who fold air quality checks into their existing risk assessment and compliance review cycle, rather than running them as a standalone exercise, tend to catch problems earlier and spend less resolving them. If it has been some time since your building's ventilation was properly assessed as part of that wider picture, that is usually the most cost-effective place to start.