Section 02 · The Chamber E-09
Loading and air change
The two numbers that decide what a chamber result means in a real building.
The two ratios that make a chamber result transferable
A chamber measurement tells you how much a material emits under defined conditions. Two of those conditions — loading factor and air-change rate — are not incidental; they are the reason the number can be used anywhere outside the test room.
Loading factor (L, units: m²/m³) is the ratio of specimen surface area to chamber volume. If you test a one-square-metre tile in a ten-litre chamber, the loading is high; scale the same tile up to a large room with the same tile area and the loading drops. The concentration the chamber measures scales with L, so the result is only meaningful if you know — and report — what L was used.
Air-change rate (n, units: h⁻¹) describes how many times per hour the chamber volume is exchanged with clean supply air. A rate of 1 h⁻¹ means one full volume replacement every hour. Higher air change dilutes the steady-state concentration; lower air change lets it build. Again: the concentration the detector sees is inseparable from this number.
At equilibrium, the steady-state concentration C in the chamber is governed by the simple relation C = (E × L) / n, where E is the area-specific rate in mg·m⁻²·h⁻¹. Knowing L and n, you can back-calculate E from C, or forward-calculate the expected concentration in a room with a different L and n — which is precisely what a product evaluation does.
Standard protocols fix both numbers to represent a reference room scenario. ISO 16000-9, the main chamber test method for building products, specifies a loading factor of 0.4 m²/m³ and an air-change rate of 0.5 h⁻¹, modelling a typical furnished space with moderate ventilation. Other standards, including AgBB and the French VOC regulation, adopt the same reference values so that results from different laboratories remain comparable.
If either number drifts — a chamber seal leaks, a flow controller miscalibrates — the concentration shifts and the back-calculated emission rate moves with it. The measurement report must therefore state the achieved L and n, not merely the target values. A reader who does not check those figures against protocol tolerances is reading the headline without reading the method.
Filed inSection 02 — The Chamber