Below are some freely adapted excerpts from ACR, The NADCA Standard (National Air Duct Cleaners Association) for the assessment, cleaning and restoration of HVAC systems (heating, ventilation and air conditioning).
The latest edition of the standard can be accessed at the following web address: http://acrstandard.nadca.com/
This standard should be regarded as a technical reference and minimum guideline for the maintenance of HVAC systems and is intended both for industry professionals and building owners.
The primary premise for using this standard is the determination of the need to clean and/or restore an HVAC system.
It is recommended that an HVAC system be cleaned when a thorough inspection shows that one or more of the following conditions exist:
- there is an accumulation of particulate debris within the system;
- system performance is compromised by the presence of contaminants;
- the system has been identified as a source of objectionable odours;
- the system is discharging visible dirt or debris into the occupied space;
- the system has been contaminated as a result of fire, smoke and/or water damage;
- the system has been infested by birds, rodents, insects or their droppings;
- the system has been identified as a potential fire hazard;
- the system has been contaminated by dust or debris resulting from building construction and/or renovation work;
- mould contamination falls within the conditions covered by points 2 and 3 above (i.e. it compromises performance and/or causes odours);
- deterioration of fibreglass components, duct liners or other porous materials is evident;
- cleaning is required as part of the regular preventive maintenance programme recommended by the system manufacturer.
Chapter 1 – Inspections
[…] Inspections should be carried out both before (to determine the need for cleaning) and after (to verify the effectiveness of the cleaning) any maintenance project. It is also recommended that scheduled inspections be included as part of an indoor air quality (IAQ) management plan.
It is recommended that system inspections be performed by experienced, qualified personnel, preferably holding appropriate certifications. Before beginning the inspection, the inspector should carry out a suitable risk assessment in order to determine any potential impact (for example, dust releases from the system) that the inspection and cleaning process could have on the indoor environment and its occupants.
[…] It is recommended that scheduled visual inspections be performed. As a minimum, components for air movement and treatment (fans, filters, heat exchangers, dampers, etc.) should be inspected at least once a year for systems installed in residential, commercial and industrial buildings. Supply and return ducts should be inspected at least every 2 years for residential systems and every year for commercial and industrial systems.
At the end of any construction or renovation work in a building, the HVAC system should be inspected to identify any dust or debris residues inside.
[…] A preliminary, specific inspection should also be carried out to check for the presence of mould and/or other biological growth. If such contamination is found, it is recommended that a more detailed qualitative and quantitative assessment be performed by specialised laboratories or competent authorities.
[…] The information collected during the inspection must be documented and evaluated to determine the condition of the system at the time of inspection. The assessment of the data must include a recommendation on the need for cleaning, a clearly defined maintenance plan including the recommended cleaning techniques, and a definition of the environmental and engineering controls required for the workspace.
Chapter 2 – Work plans
A written work plan is a document that communicates responsibilities and specific tasks associated with an HVAC cleaning project.
The main purpose of such a document is to enable the client, the cleaning contractor and all parties involved in the project to have a clear understanding of the objectives and procedures to be implemented.
The document must clearly state which system components are to be cleaned and which components are NOT to be cleaned.
[…] The work plan must clearly identify all chemical products and specific coatings to be used, including the relevant technical data sheets and instructions for use.
Where applicable, the work plan must also specify any environmental monitoring to be performed to verify worker and occupant exposure to chemical vapours and odours.
If safety and control devices in the HVAC system need to be disabled during the work, the plan must specify alternative safety measures and controls. […]
Chapter 3 – Engineering controls
Appropriate engineering controls must be implemented to ensure worker health and safety. These must include, among others: isolation barriers, dust suppression methods, HEPA vacuuming and filtration, detailed cleaning, and control of humidity and temperature.
[…] Before being brought into the work area, all equipment must be cleaned and inspected to ensure that it will not introduce contaminants into the indoor environment or the HVAC system.
[…] If vacuum equipment is used, it must be equipped with HEPA filters with a minimum efficiency of 99.97% for 0.3 micron particles.
[…] It is recommended that HEPA-filtered ambient air scrubbers be used as a supplemental control both during and immediately after HVAC cleaning and restoration work. It is recommended that such air-cleaning devices provide at least 4 air changes per hour.
[…] During cleaning operations, the HVAC system components being worked on must be kept under negative pressure to prevent particulate from escaping and contaminating indoor spaces. This negative pressure must be continuously monitored using appropriate instruments.