Section 02 · The Chamber E-10
The Decay Curve
Which day you sample is as decisive as what you sample for.
The Shape of the Curve
Open a freshly manufactured panel, fabric or flooring and the emission rate is at its highest. Load it into a test chamber, run it for a day, sample the air — and you record a large number. Run it for twenty-eight days and sample again — the number is smaller, often by an order of magnitude. Both measurements are technically correct. What makes them comparable is the protocol that fixes the clock.
Emission from most solid materials follows a characteristic decay: fast at first, slowing as the reservoir of mobile compounds is depleted, then levelling toward a near-constant background. The mathematics is often approximated as a first-order exponential, though real materials rarely behave so cleanly. Multi-phase emission — surface flash-off followed by slower diffusion out of the bulk — produces curves with shoulders and inflections that a single exponential cannot capture. What matters for the reader of a test report is that the curve is steep early on, which means small differences in sampling day produce large differences in the reported concentration.
Why the Protocol Fixes the Day
Standards that govern chamber testing — ISO 16000-9 for room-sized chambers, ISO 16000-10 for small cells — specify conditioning periods before the sample is taken. The intent is not to wait until emission has stopped; it is to move past the most volatile surface fraction and land on a section of the curve that is reproducible between laboratories. A sample taken at day three will differ from one taken at day twenty-eight, and both will differ from one taken at day one. The protocol anchors the result to a defined point on the curve so that a figure from one laboratory can sit beside a figure from another.
Where a declaration scheme sets a threshold — an area-specific rate expressed in micrograms per square metre per hour — the day of sampling is effectively part of the specification. A result reported without the sampling day, or compared against a limit set for a different day, is only superficially a measurement. The curve it sits on is unidentified.
Reading the Number
When you receive a chamber report, the first thing to locate is not the concentration figure but the conditioning time: hours in the chamber before sampling began. If the protocol is unnamed, that information may be absent entirely. A figure pulled from an early time-point on a steep part of the curve will always look worse than one from a stabilised point — and a figure presented without its position on the curve cannot be placed anywhere meaningful at all.
Filed inSection 02 — The Chamber