Introduction to IAQ and Mould: Understanding Airborne Spread and Containment

You will encounter mould on almost every water damage job that has sat for more than a day or two, and the first thing you need to understand is what it is actually doing to the air inside that building. Mould does not just sit there looking unpleasant. It actively releases microscopic spores into the surrounding air, and those spores travel. They move through HVAC systems, they drift through doorways, they hitch a ride on your clothing and your equipment. Once they are airborne, the occupants are breathing them in whether they can see the mould or not. The health effects range from mild, sneezing, itchy eyes, a scratchy throat, through to serious respiratory reactions including asthma attacks and skin rashes. People with pre-existing conditions like asthma or COPD are particularly vulnerable, and prolonged exposure can lead to mould sensitivity, a condition that causes ongoing problems like chronic fatigue, headaches, and difficulty concentrating. That is not a conversation you want to be having with a homeowner six months after you finished the job.

Here is a scenario that plays out regularly. You are called to a residential property where a slow leak behind a bathroom wall has gone undetected for several weeks. The owner has finally noticed a musty odour and some discolouration on the skirting board. As you open the wall cavity, you find significant mould growth across the framing and the back of the plasterboard. The homeowner is standing right behind you and says, "It's just a bit of mould, mate, I've been living here the whole time, I feel fine." That is your cue to have a calm, factual conversation. Explain that airborne spore concentrations are highest during disturbance, meaning the moment you start cutting or pulling material out, you are releasing a concentrated burst of spores into the living space. The fact that they feel fine now does not mean ongoing or increased exposure is safe, especially if anyone in the household has a respiratory condition or a compromised immune system.

Mycotoxins add another layer of concern that you need to be across. Certain mould types, Stachybotrys chartarum being the one most people have heard of, produce toxic substances that become airborne along with the spores. These mycotoxins can affect the immune system and contribute to respiratory illness, particularly with prolonged exposure. You do not need to diagnose anyone or make medical claims on site, but you do need to understand that the contamination you are dealing with may carry risks beyond simple allergic reactions. This is part of why your containment and PPE decisions matter so much, not just for the occupants, but for you and your crew working in that environment every day.

Practically, what this means on the job is that your first priority before any disturbance is to limit the spread of airborne spores. Before you touch a single piece of contaminated material, you should have your containment in place and your PPE on. Negative air pressure inside the work zone, physical barriers between the affected area and the rest of the building, and proper respiratory protection for your crew are not optional extras. They are the baseline. If an assessor or loss adjuster asks why you have set up containment before starting demo, the answer is straightforward: "Once we start disturbing this material, spore counts in the air spike significantly. Containment protects the rest of the property and the people in it." That is a response that demonstrates competence and protects you professionally. Understanding how mould affects IAQ is not just background knowledge. It directly shapes every practical decision you make from the moment you walk onto a contaminated site.