Mould outdoors is not much of a problem, however mould growth indoors can have harmful effects on both property and the health of the people inside.  As well as posing health risks to people in the building it invades, mould can gradually damage building materials and furnishings and even cause structural damage.

What can be done about mould?

While in our normal environment it is impossible to eliminate mould entirely, it is possible to prevent mould growing - but this takes awareness and effort, and is easier than mould remediation projects. Moulds can grow almost everywhere and on any surface as long as moisture is present. Reducing indoor moisture as much as possible will reduce the possibility of indoor mould.

Moisture, however, is a fact of life in almost all buildings. Changes in construction since the 1970s have resulted in tightly sealed buildings with diminished ventilation. In addition to this, a second and common source of moisture is water leaks and spills, which occur regardless of the age of the building. However, a thorough drying and/or removal of water-damaged material will prevent or limit mould growth.

Advice for Reps

As reps, you should include looking for mould as part of your regular workplace inspections, and following heavy rain or spills. The employer/occupier of the workplace should ensure timely maintenance and the prompt repair of all plumbing and building structure leaks.

Mould prevention tips include:

  • Maintaining indoor relative humidity between 30 and 50 per cent
  • Identifying condensation and wet spots
  • Preventing condensation by increasing surface temperature, through insulation or increased air circulation, or by reducing humidity through repair of leaks and - depending on the outside air - ventilating or dehumidifying
  • Insulating cold surfaces to prevent condensation on piping, windows, exterior walls, roofs and floors where possible
  • Keeping HVAC (Heating Ventilation and Air Conditioning) drip pans clean, flowing properly, and unobstructed
  • Performing regularly scheduled building/ HVAC inspections and maintenance, including filter changes (see Australian Standard AS 3666.2)
  • Venting moisture-generating appliances, such as dryers, to the outside where possible
  • Venting kitchens (cooking areas) and bathrooms (there may be local requirements)
  • Using exhaust fans when cooking, dishwashing, or laundering (especially in the food service or laundry areas) or when cleaning large areas
  • For floors and carpets, removing spots or stains immediately. Reduce the amount of water used when cleaning carpets as much as possible.
  • Providing adequate drainage around buildings and sloping the ground away from building foundations

Remediation includes identifying and correcting the conditions that permitted the mould to grow and taking steps to properly remove mould-damaged materials. The highest priority must be to protect the health and safety of the building occupants and remediators. This is particularly true if it is known or suspected that the HVAC system is contaminated, as it could spread contamination throughout the building. If the water or mould damage was caused by sewage or other contaminated water, it is extremely important that a qualified professional be consulted.

Remediation plans may vary greatly depending on the size and complexity of the job. As a general rule, simply killing mould, for example, with biocide is not enough. It must be removed, as the possible chemical byproducts (toxins) could be present even in dead mould. 

The specific method(s) used will depend on the type of material affected and the scope of the contamination. Trained clean-up personnel should use appropriate protective equipment such as respirators and gloves during cleaning activities.

Approaches include:

  1. Wet Vacuum
    These can be used to remove water from floors, carpets, and hard surfaces where water has accumulated but should not be used on porous materials, such as gypsum board. If there is insufficient liquid present, spores may be exhausted indoors. Cleaning equipment is also important because mould spores may adhere to equipment surfaces.
  2. Damp Wipe
    Mould can generally be removed from nonporous, contaminated surfaces by wiping or scrubbing with water and household bleach and then drying the surface thoroughly to discourage further mould growth. Proper personal protective equipment (P2 respirators) must be worn to avoid inhaling the mould spores.  A  half-face respirator with cartridge may not stop inhalation of chemical vapours, however.  (Note that bleach may damage some surfaces - if unsure, contact the manufacturer.)
  3. HEPA Vacuum
    HEPA (High-Efficiency Particulate Air) vacuums are recommended for final cleanup of remediation areas and for dust that has settled outside the affected area. Ensure that the filter is properly seated so all the air passes through it. Use protective equipment to change the vacuum filter and to dispose of the filter and contents in impermeable bags or containers.
  4. Use of Biocides
    The use of a biocide, such as chlorine bleach, is not recommended as a routine practice during mould remediation. In most cases, the areas cannot be truly sterilized - although this is not the main aim of the use of biocides; a level of mould spores will persist in the air similar to the level in the outside air. The good news is that the spores circulating will not cause further problems once the moisture level in the building has been corrected.

    Do not use fungicides indoors if they were developed for outdoor use, such as hexachlorobenzene, organomercurials, pentachlorophenol, phthalimides, and dithiocarbamates, as they can be extremely toxic to animals and humans in an enclosed environment.

Bottom line: mould has no place indoors and must be prevented at the source - eliminate excessive moisture and dampness!

This information is only a summary of basic procedures and is not a detailed guide to mould remediation. It is highly recommended that experts be consulted and trained clean-up personnel be engaged to handle mould contamination. Remember: the employer/occupier of the workplace has a duty under section 21 of the OHS Act to provide and maintain a safe and healthy workplace.

Legal Standards

Employers have a duty under the Victorian Occupational Health and Safety Act (2004) to provide and maintain for employees, as far as practicable, a working environment that is safe and without risks to health (Section 21). This includes providing a safe system of work, information, training, supervision, and where appropriate personal protective equipment. The employer must identify hazards in the workplace and, if practicable, eliminate these hazards. If this is not practicable, then the employer must take measures to control the hazard and reduce the risk to workers.

Further, under Section 22, the employer must monitor the health of employees [22(1)(a)] and monitor the conditions at the workplace [22(1)(b)].  In addition to this, under Section 22(2)(b), the employer must 'employ or engage persons who are suitably qualified in relation to occupational health and safety to provide advice to the employer' if necessary.

Persons who manage or control workplaces also have a duty (under Section 26) to take 'measures as are practicable to ensure that the workplace is safe and without risks to health'.

International standards:
Health Canada guidelines state that acceptable readings of airborne mould can be up to a maximum total of 150 colony forming units per cubic metre of air.

The World Health Organisation (WHO), however, states:

"As the relationships between dampness, microbial exposure and health effects cannot be quantified precisely, no quantitative, health-based guideline values or thresholds can be recommended for acceptable levels of contamination by microorganisms.

Instead, it is recommended that dampness and mould-related problems be prevented. When they occur, they should be remediated because they increase the risk of hazardous exposure to microbes and chemicals."

Where can mould grow?

A key characteristic of mould is its ability to grow without sunlight. All it needs is a viable mould spore, a nutrient source, some humidity and moisture to thrive. Mould is often found in damp, dark and hidden spaces. Mould spores can be released into the air when mouldy material becomes disturbed. Mould also 'sporulates' when humidity and temperature fluctuate outside of ideal growing conditions. Exposure occurs when the spores are inhaled - or land in an open wound.

How much of a problem is mould?

Generally, limited exposure to most types of moulds does not cause symptoms in healthy people. However, some moulds may be hazardous for those with allergies or other health issues, or when people are exposed to certain moulds for prolonged periods. Some clinical studies have also suggested that mould allergy is connected to severe asthma. 

People who have asthma, bronchitis, hay fever, other allergies, uncontrolled diabetes or have weakened immune systems, are more likely to react to mould.

Of more concern, however, is that many of these moulds make "mycotoxins", by-products that are toxic to humans. These toxins can slowly wear down the immune system and can lead to allergic or respiratory problems.  Some are documented carcinogens.

The most common symptoms reported are runny nose, eye irritation, skin rash, cough, congestion and aggravation of asthma. People with serious allergies to moulds may have stronger reactions that include fever and shortness of breath. People with chronic illnesses, such as obstructive lung disease, may develop mould infections in their lungs.

Over the past few years, there have been repeated floods in Eastern Australia, and this has exacerbated the problems associated with mould. For more information: Floods herald creeping problem of mould and growing health risks  a March 2012 article by Monash academics Tom Jeavons and Michael Abramsoney in The Conversation.


A water-damaged workplace may lead to a dramatic increase in the rate of asthma and other breathing problems in employees, and could be a substantial source of sick days, recent research suggests.

In a study of workers at one leaky, mould-contaminated office building, scientists from the US government's workplace safety research body NIOSH found that the rate of adult-onset asthma among employees was more than three times that for the general population. Two-thirds of these cases were diagnosed after the employees had started working in the building. The researchers estimate that up to 12 per cent of employee sick days in a year could be attributed to the health effects of the building. 'We feel our study adds to the evidence that asthma can develop in damp indoor environments,' said NIOSH researcher Dr Jean M Cox-Ganser.

The exact triggers of the workers' breathing problems were not clear, however. Allergic reaction to mould is one possibility, Cox-Ganser said, but damp environments can create a number of exposures potentially irritating to the airways. Writing in the journal Environmental Health Perspectives, the researchers conclude: 'This investigation documents the considerable respiratory illness, adverse effects on quality of life, and absenteeism that have placed personal, social, and economic burdens on many employees and their employers. Building-related respiratory disease warrants increased public health, medical research, and policy attention.'

(Jean M. Cox-Ganser and others. Respiratory morbidity in office workers in a water-damaged building. Environmental Health Perspectives volume 113, number 4, pages 485-490, April 2005 [Abstract]) 

And more recently: M. Cox-Ganser, Indoor dampness and mould health effects – ongoing questions on microbial exposures and allergic versus nonallergic mechanisms NCBI. This article provides an overview of a number of more recent studies, and meta analyses of studies, looking into a number of questions on health effects of mould. 

See Also:

Last amended August, 2021