The capacity of mould to linger in the air and to spread between indoor spaces has perplexed many poor souls who suffer breathing difficulties and mucosal tissue irritation
So how does mould linger so much longer in the air than ordinary dust does? Also, what can be done about it?
Spores are the seeds of mould. Moulds are fungi. So moulds are tiny, mushroom-like organisms, living things which grow rather like bacteria, eating nearly anything they come across, and they are kept at bay by dryness, sunlight, and cleanliness.
The reasons why spores hang around are profound. It has to do with the shape and surface characteristics of spores, especially chains of spores. Mould spore aerodynamics and spore detection are growing fields of research, and the capacity of mould spores to form chains forms the core of the research.
Under the microscope, mould spores can look beautiful due to their chain-forming habit, like pearls on a necklace. Why they produce these chains at all, rather than only individual spores, evaded our understanding throughout much of the history of microscopy, but the answer is now coming to light. One would have naturally thought the function of the chains was merely to break apart, so producing individual spores, like seed heads do on plants.
In fact, the nature of spore chains is tactical, like pollen in flowers, which seeks a carrier. While bees carry pollen from flower to flower, the carriers for mould spore chains are the air currents.
If a parachutist is asked to stay in the air for very long periods, and they have a choice of a large or a small parachute which would you suppose they’d like to choose? If the parachutist is also asked to perform these long stays in the air by catching thermal updrafts, which shape of parachute should they choose? If you’ve seen the elongated rectangular parachutes in documentaries or those that land at the footy grand-final, you might ask the experts whether that rectangular and performance-shaped parachute may be the obvious choice. They’ll tell you that an ability to spread out across the thermal turns out to be a factor, as does an ability to generate turbulence. Square, rectangular and lenticular shapes do all this.
A chain of mould spores is an elongated shape, a shape which catches air currents more readily than a sphere does. Individual spores, each a rough sphere, can break off at any point, and settle relatively quickly into a location distant from their point of origin. Germinating at the new site, they have then achieved their fate. More likely though, the chain stays intact, and they all land and germinate together.
The other characteristic of mould spores that keeps them afloat is their ability to repel water. This ability is not complete, as they also need to absorb water to germinate, but they prioritise spreading over germinating as there is little point germinating right where their parents raised them. They need new pastures. By repelling humidity droplets and other damp particles, they stay firmly in the dry fraction of dust, and so can avoid being dropped out onto the ground or the floor by gravity, at least for some considerable time.
Before getting into what can be done about this to control breathable air for hygiene, it’s worth dwelling on what the characteristics of spore propagation mean for air management in the built environment. Inside a building, we generally regard each room as being separate. We can often control variables like temperature by opening or closing doors, and so allowing or preventing the mixing of air. However, this ability is rather overhyped in our minds since no matter how hard we try to keep a room isolated, the room remains part of the airflow inside the building. We can only speed up or slow down the mixing.
The same that holds true for temperature and humidity, also holds true for particles like mould spores and pollution; they can travel from room to room, it’s only a question of amount. Since mould spores can be harmful in relatively small quantities, this really matters. The potential harm lies not so much in being breathed in in small quantities, but rather in being propagules for germination and subsequent amplification wherever the spores find a damp spot to colonise.
A commendable practice which is entrenched, is to seal off the infested area, to prevent spread during remediation. But spores may have already spread – has the horse already bolted before the area was isolated and remediation begun? It would be useful to take spore counts in the air in adjoining rooms before assuming they are already clear prior to treatment. In some cases, the area needing to be sealed off may be an entire floor of the affected building. Heating, ventilation and air conditioning (HVAC) ducts are another means of spread for spores. Basically, a lot of doors are open to newly graduated spores; the world is their oyster.
Once sealed off, an affected area needs to be treated in two ways. Both the visible infestation and the air itself need cleaning to eliminate the mould. Traditionally, air scrubbers have been used, as well as ventilating directly to the outside air. Dampness is dried out, and mouldy surfaces are either replaced or cleaned.
Counting the number of spores in the air comes in handy again after the restoration, or renovation and remediation work is complete, just to show a clearance. The mobility of spores means that it may be advisable to take a wider area of sampling for clearance testing, rather than just monitoring the rooms that had been visibly affected by mould.
New findings seem to indicate that spores can be inactivated and disabled in situ, both in the air and on surfaces. They may be hardy organisms but they cannot survive everything that’s thrown at them. Like us, they’re clever but opportunistic, and they invest or gamble on a particular strategy. That pays off well when the strategy is fit for purpose, but not at all well when their strategy doesn’t match the ambient conditions.
Surfactants are among the classes of compounds that moulds do not like or tolerate well. Use of rigorously researched surfactant combinations can prevent spores germinating by interfering with both their ability to be airborne and also their ability to absorb pure water. Hence, once settled out of the air, the treated spores cannot grow. Of course, use of such products requires the right training in order to even contemplate using them or touching them at all. If the products are employed, those residues must be cleared from the air before occupants move back in.
The existing processes of renovation as currently and formerly practiced are the most appropriate in many cases. However, the number of cases being deemed fit for rapid remediation rather than slow renovation may be gaining gradually in frequency, because the new approach takes into account the presence of spores across a wide number of rooms, and because the air treatment and particle monitoring processes are relatively cheap. It goes without saying that both the visible mould and the airborne moulds must be inactivated, and also then removed.
Any decision to renovate or remediate a surface must be made on a case by case basis, with respect to what proven technology is at hand, and is trusted, precedented and documented, as well as meeting the guidelines of the building owner or operator and best practice. For instance, often air scrubbing is the warranted procedure. Drying equipment is sometimes used, and on the other hand sometimes is not required. All such procedures are like a set of tools; you choose the right ones for the job facing you.
The restoration industry probably does not expect the norms of building design and construction to change suddenly, to minimise moisture entry and to minimise dewpoint occurring. The mould problem is not going away expediently on a society-wide level. Just like achieving the right heating or cooling or light and humidity, constant maintenance is also in order for airborne particle concentrations.
Whether a building is “sick” itself or there is building related illness, even Monday Fever, there are approaches which can resolve these issues. HVAC ducts can be cleaned as well as air and visible surfaces can. Why wouldn’t that be done if the ducts are clearly places where moulds grow, and if there is a known mould emission from the ducts? Cost considerations, and a tendency to act as if what can’t be seen may be overlooked, can all be put into better perspective when avoidance of potential occupant downtime through sickness is factored in.
The building owner, operator or leaseholder has an asset which retains value best by being protected. Furbishing materials don’t last forever, or remain unsoiled for long. Like a car, regular servicing can pay off, to ensure that the furbishing materials last as long as possible.