S.A. Industrial Services (Qld) Pty Ltd

How often should your ducts be cleaned?

HVAC system hygiene is an important part of the operation of any building and depending on the building use it can be absolutely critical.

The awareness of indoor air quality (IAQ) is increasing every day.

Regular visual inspections are the best way to realise when HVAC cleaning and decontamination should be conducted.

Research concludes that new ducting should be cleaned before occupancy begins.
NADCA standard "ACR 2002 Assessment, Cleaning & Restoration of HVAC Systems" (which is an industry standard) also calls for newly installed HVAC systems and the ducting to be cleaned before being operated.
After post construction decontamination and cleaning of all components and the ducting, the emphasis should be placed on regular scheduled inspections to determine the need for future cleaning and decontamination.

Factors to consider:
  • Varying operating hours
  • Adjacent site interferences
    • Local construction activities
    • Poor maintenance
    • Poor filtration etc.
The only real way to know is regular inspection.


It is not uncommon to find debri left over from construction with no explainable reason for their presence and no possibility of these items entering the ducting in the normal course of operation. Such items include old newspapers, HVAC drawings, hard hats, torches, tools, bird nests, lunch boxes, takeaway wrappers and an array of other items.

Depending on usage and history of the building and the materials used to constuct it, HVAC systems may become contaminated with hazardous materials.
Older facilities in which asbestos was used in the initial construction may have collected asbestos dust within their HVAC systems.

Leaking water pipes above ducting will eventually corode the ducting and allow water to enter the ducting. The presence of of high humidity or water damage in ductwork can lead to significant microbiological contamination.

Biological contaminants, caused by the accumulation of dust and debri combined with appropriate moisture levels that are present in HVAC systems, that can be potentially distributed to occupied spaces include:
  • Bacteria
  • Fungi (Mold & Mildew)
  • Viruses
  • Dead vermin
  • Mites
  • Insects
  • Pollen
Microbiological contamination in a HVAC system may cause allergic reactions amongst sensitised building occupants, and pathogenic or toxic species may lead to more serious illnesses such as Hypersensitivity Pneumonitis.

Musty odours from supply diffusers may indicate fungal growth within the HVAC system, but there could be other sources also.
The location and concentration of nuisance dusts, microbial growth sites and other debris indicate the need for system cleaning and decontamination procedures.


Visual Inspection Program

ACR 2002 Assessment, Cleaning & Restoration of HVAC systems, sets out a visual inspection program that should form part of all facilities Indoor Air Quality Management Plans and Procedures.

The table below indicates HVAC cleanliness inspection schedules for different building use classifications.

  Air Handling Unit Supply Ductwork Return Ductwork & Exhaust
Industrial 1 year 1 year 1 year
Residential 1 year 2 years 2 years
Light Commercial 1 year 2 years 2 years
Commercial 1 year 2 years 2 years
Healthcare 1 year 1 year 1 year
Marine 1 year 2 years 2 years

Kitchen exhaust ducts

Table 11: Frequency of Cleaning
Heavy Use 12-16 hours per day 3 monthly
Moderate Use 6-12 hours per day 6 monthly
Light Use 2-6 hours per day 12 monthly

Legal Issues


Australian lawyers have predicted an increase in claims for "Sick Building Syndrome" and "Building Related Illnesses" as Australian building occupants become more likely to seek remedy to complaints in the courts.
Their predictions for the increase are based on:
  • An increase in "Sick Building Syndrome" litigation in the United States;
  • Reported legal cases in Australia;
  • Changes to Australian law which make it easier for groups of people to mount class actions; and
  • Australia's move towards contingency fees - a system where lawyers essentially take a percentage of the damages awarded to their clients as their fee.
Legal issues regarding indoor air quality are generally concerned with the legal obligations and duties of property owners and managers. However all people who are associated with buildings and services also have responsibilities.
In broad terms we can divide the issues into two categories:
  • Building owners and occupiers
  • Employers

Building Owners and Occupiers - Duties of Care

At common law, occupiers of land and premises owe a duty of care to persons entering their premises and may be liable for illness (injury) suffered by them. This liability is governed by the general principles of negligence.
To determine an occupier's liability all the relevant circumstances are considered; in particular:
  • the nature of the occupier's occupation of premises; and
  • the manner of the entrant's entry.

There must be a reasonable foreseeability of a real risk of injury to the entrant or to the class of person of which the entrant is a member.

A risk of injury which is unlikely may be foreseeable so long as the risk is not farfetched or fanciful.

An occupier's obligation is measured by the standard of reasonable care.

A building owner may be liable for injury suffered by entrants caused by faulty air conditioning where the building owner has been warned of the defect in the air conditioning by an expert.

Similarly, if a manufacturer warns a building owner of a risk involved in the use of a faulty air conditioning unit and injury is suffered by people entering the building as a result of the defect, the manufacturer has fulfilled the common law duty of care it owes to the building owner. However, the building owner will be liable as an occupier for the injury suffered by the entrant.

Australian standards, particularly AS 1668 Part 2 and AS/NZS 3666, are relevant to duty of care and it could be argued that the risks associated with the failure to meet these standards would probably be reasonably foreseeable.

A defendant in an indoor air quality case whose building failed to comply with any relevant requirement of these standards would be hard-pressed to escape liability.

Occupiers and owners each have responsibilities. Control is the primary factor in assessing liability. It is not necessary that a person should have the entire control over premises in order to be an occupier. Nor is it necessary to show exclusive occupation. It is sufficient if a person has some degree of control such as that given by a legal right to invite the Plaintiff to enter the premises.

It is not necessary to be in actual physical possession of premises in order to be an occupier of them. In addition, there may be more than one occupier of the same premises. Two or more persons may be occupiers. Wherever there are two or more occupiers each is under a duty to use care towards persons coming onto the premises. This duty depends on the occupier's degree of control.

Note that when a danger exists next to the area controlled by an occupier, it may owe a duty of care to persons injured by the danger whether or not it is in control or occupation of that area. When a Plaintiff has been forced to use adjacent land because of conditions on the occupier's land, liability is usually attributed to the first occupier, not to the occupier of the adjacent land.

There are a number of legal defences to negligence, for example the voluntary assumption of risk. For a Defendant to have the benefit of the defence that the Plaintiff voluntarily assumed the risk of injury, the Defendant must prove on the balance of probabilities that the Plaintiff consented, expressly or impliedly, to the risk.

Employers' Duties of Care

Property owners and managers also have obligations as employers.

At common law, a worker injured in the course of employment could sue the employer in negligence. Common law negligence is established by proving the existence of a duty of care, the breach of that duty and a causal relationship between the breach of duty and the original injury complained of.

At common law an employer owes a duty to take reasonable care for the health and safety of each of its employees.
This duty requires that the employer provide:
  • Safe and healthy premises;
  • safe plant and equipment; and
  • a safe system of work;
for each employee.

The standard of care is reasonable care, and what is reasonable will depend upon:
  • the probability of foreseeable harm;
  • the gravity of the harm that was foreseeable; and
  • the practicability of adopting measures to prevent foreseeable harm.

It is important to stress that the duty is owed to each employee as an individual. If the risk is greater to one employee than to another - for example, because of an allergy or peculiar susceptibility - then the duty owed will be greater. Likewise, if the consequences of injury are greater.

This duty cannot be passed to another by contract although, should an employer engage a contractor to maintain safe premises for the employer's employees, the employer may be able to recover from the contractor either in contract or in negligence in the event that the employer was found liable to an employee for failing to provide safe premises.

Thus, it may be that the employer would be required to do all that is practicable to be satisfied that the HVAC system was safe and without risks to health. If the building owner refused to co-operate and there was evidence of a foreseeable risk that the building was contaminated, the employer may be required to remove its employees. This would be akin to shutting the factory should the risk warrant it.


Duty of Care Consequences

Where a person sustains an injury caused by poor air quality due to a faulty HVAC system that person may have a claim against the building owner, employer tenant, manufacturer, and/or the designer or installer, of the system.

Indeed all of these parties may be liable as follows:
  • The building owner may be liable as an occupier at common law, under the relevant Occupational Health and Safety Act, and the relevant Public Health Act;
  • The employer may be liable at common law and under the Occupational Health and Safety Act and Worker's Compensation Act;
  • The manufacturer may be liable at common law and under the Occupational Health and Safety Act and Trade Practices Act; and
  • The installer may be liable at common law and under the Occupational Health and Safety Act.
It may eventuate in a case that all these parties are liable but that there is an apportionment of liability between the parties.

Other Legal Issues Other legal issues include

  • Occupational health and safety legislation
  • Requirements for Legionella control
  • Workers compensation liabilities for injury.

Liabilities under these headings can be very strict. Once a causal connection is made between a plaintiff's illness and, for example, the air conditioning system serving a building then liability accrues regardless of the measures taken by the employer.

A special case in point concerns passive smoking, i.e. inhalation of tobacco smoke by non-smokers.

The Full Court of the Australian Federal Court found that there is considerable evidence of a connection between passive smoking and lung cancer, asthma and respiratory diseases.

In the context of compensation available to employees for diseases attributable to or aggravated by their employment, the inhalation of cigarette smoke by non-smoking employees in the workplace has resulted in successful compensation claims for illness caused by passive smoking.


Steps to Minimise Litigation Risk

Protection from litigation is not just the realm of the building owner, occupier or the employer. In the event of a claim the plaintiff will often make a claim against multiple parties and in turn these parties will look to identify other defendants to whom they might, in turn, direct the liability.

Apart from legal obligations and duties of care, relevant parties should exercise vigilance in additional areas including:
  • Insurance;
  • Document retention - ensure that adequate records are kept in relation to HVAC maintenance and records of suppliers of products that may contribute to poor indoor air quality. Refer AS/NZS 3666 Part 2.

With reference to potential breaches of environmental statutes, corporate officers should take steps and develop a compliance system to enable them to demonstrate that they use "all due diligence" to prevent breaches of legislation. Such a compliance system must be supervised and reviewed to ensure its effective operation.

In relation to risks, the best defence is to manage risks before claims are made. This involves an ongoing program of monitoring relevant environmental conditions in a workplace or building. The programs need to be well documented and any remedial action identified under the program should be addressed as failure to do so may provide incriminating evidence that proves no action was taken.

Some programs adopted go further than ensuring environmental and OHS laws and standards are complied with and it is desirable that they do to minimise legal risks. In areas where scientific knowledge is evolving such as indoor air quality such a program should also monitor the state of the evolving knowledge and assess the implications of that knowledge. If scientific knowledge progresses in such a way as to indicate a particular risk in circumstances that are manageable, it will be wise to react to that knowledge. Any industry or commercial undertaking that does not take these steps will ultimately be more vulnerable to prosecution and civil liability.


The Right To Healthy Air

In 2000, a WHO working group prepared nine statements on rights to healthy indoor air. These statements have been endorsed by other recognised bodies such as the International Society for Indoor Air Quality and Climate, have already entered the curricula of tertiary educational courses and have been used in lawsuits.

The statements, without interpretation or comment, are:
  • P1: Under the principle of the human right to health, everyone has the right to breathe healthy indoor air.
  • P2: Under the principle of respect for autonomy (self-determination), everyone has the right to adequate information about potentially harmful exposures, and to be provided with effective means for controlling at least part of their indoor exposures.
  • P3: Under the principle of non-maleficence (doing no harm), no agent at a concentration that exposes any occupant to an unnecessary health risk should be introduced into indoor air.
  • P4: Under the principle of beneficence (doing good), all individuals, groups and organisations associated with a building, whether private, public or governmental, bear responsibility to advocate or work for acceptable air quality for the occupants.
  • P5: Under the principle of social justice, the socioeconomic status of occupants should have no bearing on their access to healthy indoor air, but health status may determine special needs for some groups.
  • P6: Under the principle of accountability, all relevant organisations should establish explicit criteria for evaluating and assessing building air quality and its impacts on the health of the population and on the environment.
  • P7: Under the precautionary principle, where there is a risk of harmful indoor air exposure, the presence of uncertainty shall not be used as a reason for postponing cost-effective measures to prevent such exposure.
  • P8: Under the `polluter pays principle', the polluter is accountable for any harm to health and for welfare resulting from unhealthy indoor air exposures). In addition, the polluter is responsible for mitigation and remediation.
  • P9: Under the principle of sustainability, health and environmental concerns cannot be separated, and the provision of healthy indoor air should not compromise global or local ecologic integrity, or the rights of future generations.