Two homes give the same reading on an air quality monitor.
The same number of fine particles, the same figure on the screen. By every ordinary measure they are identical.
I am fairly certain one of them is harming the people inside it and the other is not.
That belief is the reason for everything I am about to describe, and I want to set out the reasoning honestly, including the parts we have not finished.
Think of the particles in your air as trucks on a road. Every air quality test in ordinary use counts the trucks. More trucks, worse score. Fewer trucks, better score. It is a reasonable start, and for a long time it was the best anyone could do.
But a truck is only as dangerous as what it carries. One may be loaded with sand. Another with something that burns. From the roadside they look identical, and a count scores them identically. Anyone who actually cared what reaches you would want to know the cargo, not the traffic.
Indoor air behaves exactly like this. Particles of the same size and number can carry completely different loads. Some are close to inert. Others are chemically reactive, coated with metals, combustion residues, and a class of long-lived reactive compounds that keep working long after the particle itself has settled.
Same count. Different cargo. Different effect on the person breathing it.
The ordinary chemistry inside your cells produces reactive molecules, and your body neutralises them as it goes. Health, at the cellular level, is that balance holding.
Some of what you breathe tips it. The material arrives already reactive, or it provokes reactive chemistry once it is inside you, and your defences are spent faster than they can be replaced. The strain this creates is called oxidative stress. The capacity of a given material to generate that strain is called its oxidative potential.
Oxidative load is the sum of that burden in a particular space. Not how much material is present, but how much oxidative strain the air, dust and surfaces of that room are capable of producing.
It is the difference between the sand truck and the one that burns.
Almost all indoor air assessment measures concentrations and compares them against a threshold. So many micrograms of this, so many parts per billion of that. That work matters and I am not dismissing it.
But a concentration is a count of trucks. A space can sit comfortably beneath every published limit and still carry a high oxidative load, because what is present, though modest in quantity, is highly reactive. The reverse holds too. A higher concentration of largely inert material may matter considerably less than a low concentration of something aggressive.
If that is right, then a building can pass every test we currently run and still be doing something to the people inside it. That possibility is what I find difficult to put down.
There is a particular reason this is easy to miss indoors.
Some of the most reactive material does not disperse the way a gas or a smell does. A class of these compounds, known as environmentally persistent free radicals, is unusually stable. They bind to dust and to particles and stay reactive for a long time, sitting in the settled dust on a ledge or in the fibres of a carpet, continuing to generate strain day after day.
So a room can look immaculate, smell of nothing, pass a conventional test, and still carry a burden that no count will reveal. The cargo has been unloaded and left in the room.
Air is the clearest way to see the principle, and it is what people worry about first. But the same logic runs through everything indoors.
Water carries its own load between the tank and the tap, and what is dissolved or growing in it matters far more than whether it looks clear. Surfaces are never neutral either. The most persistent material does not stay airborne at all. It settles, and it works from there.
The cargo arrives by more than one road, which is why I do not think air can sensibly be assessed on its own.
If the burden is what matters, then it should be possible to measure it and express it as a single figure. That is what we are building with the Oxidative Load Index®.
The idea is a number from 0 to 100 that describes the oxidative burden of a space. It works in the spirit of a credit score, which takes a great many separate facts and resolves them into one figure a person can read at a glance and act on. Ours is not drawn from the air alone. It integrates the reactive chemistry of the air, the composition of the particles and what they carry, the load in the water from the tank to the tap, the reactive material settled on surfaces and in dust, the biological load from damp and microbes, and the conditions that let all of it thrive or fade. Air, water and surfaces, read as one environment rather than three separate tests, because that is how a building actually acts on the people inside it.
Some of what it measures is ordinary and some of it is not. Counting particles is routine. Measuring what those particles are capable of doing, their oxidative potential, and detecting the environmentally persistent free radicals that lodge in household dust and go on generating strain for months, is not. That is frontier chemistry, and it is the part almost no one applies to a home. It is also the reason the index exists at all: the hard measurement is the whole point.
Two things make it ours rather than anyone's, and only one of them can be seen. The first is the method, the particular way we combine those readings into a single score, and that stays in our laboratory. The second matters more and cannot be copied at all: every audit we run adds to a reference database of real readings from real buildings in this climate, built over years. A score means something only when it is measured against that accumulated body of local data. The concept is open science, and anyone may have it. The database is not, and it is what the number is read against.
Now the part most companies would leave out.
The science underneath the index is well established. That the reactive capacity of a contaminant matters, and not merely its quantity, is not controversial in environmental research; it has been studied for years. What is new is applying it to indoor spaces, at this breadth, as a single usable measure.
The particular way we resolve our readings into one score is ours, and it is still in validation. It has not been externally validated or peer-reviewed, and I will not describe it as either until it is. We are standing up the laboratory methods now, in our own microbiology laboratory, and we are seeking independent validation of the approach from research institutions that specialise in this chemistry, rather than rely on our own word for it.
There are things I cannot yet tell you, and I would rather say so than pretend otherwise. I cannot tell you our thresholds are the final thresholds, because thresholds are the hardest part of any index to prove, and ours are working figures drawn from our own sampling and sharpening as the database grows. I cannot tell you our weightings are settled, and we deliberately weight no part above another yet, because we will not claim that one matters more than the rest until we can show it.
A number that arrives fully formed, with no account of how it was built or how far it has been tested, is asking for faith. I have spent seventeen years arguing that this industry asks for too much faith and offers too little proof, and I am not going to make the same move myself the moment it becomes convenient.
So this is where we are. A theory I believe is correct, an instrument built to test it, and an honest account of what remains unproven. If the validation goes against us, I will say so here.
What I am confident of is the underlying question. We have spent decades measuring how much is in our air, and almost no time measuring what it does. In a region where we spend nearly all our lives indoors, in sealed buildings, breathing air that has been recirculated many times over, that seems to me the wrong way round.
We have spent decades measuring how much is in our air, and almost no time measuring what it does.
Oxidative Load Index® is a registered mark of Saniservice.
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