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Sick Building Syndrome (SBS)
24 May 2004

John Herbert, hong kong energy saving expert, BEAM expert
John Herbert

SBS a working definition

Sick Building Syndrome (SBS) is a health condition caused by the poor Indoor Air Quality (IAQ) or sub standard ambient conditions found within a specific building.

A number of other terms have emerged over the years, problems have been described as Building Related Illness (BRI), Tight Building Syndrome (TBS), Sick Buildings, etc. However, SBS is probably most widely excepted terminology.

Occupants suffer from a variety of ailments including, but not limited too, mild respiratory distress, coughs, dry throat, headaches, eye strain, sleepiness, dizziness and general discomfort. SBS may even manifest itself differently, within occupants of the same building.

If symptoms apparently disappear after leaving the workplace SBS maybe the reason.

Buildings found with excessive carbon dioxide (> 1000ppm) are prime candidates for causing SBS.


Independent survey's in Hong Kong have revealed that more than thirty percent (30%) of office buildings suffer from poor IAQ. Therefore, it is no surprise to discover a correlation with excessive or prolonged employee absence.

However, we must consider that the survey's were somewhat biased towards blue-chip organisations and government buildings, therefore based on my experience of Hong Kong buildings, a realistic estimate of fifty percent (50%) or more would be more accurate characterisation.

SBS most often discovered where buildings have a sealed envelope, designed to prevent infiltration/exfiltration (sealed windows) requiring complete reliance on the mechanical ventilation system. And older buildings where equipment maintenance is lacking.


Solving SBS and related IAQ problems is not a black art, solutions for buildings suffering Sick Building Syndrome usually include the following strategies:

  • Fresh Air Assessment / Improvement
  • Contaminant Removal at Source
  • Planned Preventive Maintenance (PPM)
  • Communication

Fresh Air

Provide adequate fresh air. Now that might sound simple, it is, however fresh air is not free. Providing or increasing fresh air allowances dramatically increases energy consumption, and hence the cost of ownership.

Also one must consider that the “fresh air” in urban environments can hardly be described as healthy. Hong Kong's Air Pollution Index (API) frequently exceeds the danger threshold (API exceeding 100), Causeway Bay and Mong Kok districts being the worst offenders.

Increasing fresh air, or providing 7-10 litres/sec/person dilutes pollutants generated by occupation. However, depending on the external environment (source for the fresh air) adequate filtration and air cleaning is required.  Presently, most buildings in Hong Kong have inadequate filtration (due to the existing fire regulations) therefore polluted, contaminated outside air is drawn into buildings and circulated through the occupied space.

Air Cleaning

Filtration is an vital element of every ventilation system.  However, economic pressure on the maintenance budget, especially in older buildings, can lead to neglected maintenance and filters.  Air filtration is the first line of defence, particulate matter bypassing filters may settle in other parts of the system, e.g. ductwork, dampers, fittings or physically distributed in the occupied area. Once past the filter, it is an expensive and disruptive operation to remove.  Have sufficient access panels been installed? they are need to inspect the ductwork and provide access for duct cleaning equipment.

Mechanical type filters such as the typical panel and bag type filters are relatively inexpensive but do not effectively capture and retain small particles. Higher performance air filters such as HEPA filters (used in hospitals and clean rooms) capture these smaller particles but are expensive.  Maintenance is the key, look at your filters today, you may be shocked, look through microscope and you would be horrified.

These mechanical type filters do not remove odour or gaseous pollutants (for example VOC). Certain specific gaseous pollutants can be removed by charcoal filters, but these are expensive and require frequent replacement.

Contaminant Removal at Source

One of the first tasks is identification and remove the contaminant source. Removing the pollutant at its source is the most effective approach for resolution of indoor air quality (IAQ) problems, when the source can be identified and control is economically feasible. Examples include:

  • routine maintenance of HVAC systems, e.g. periodic cleaning or fitting new filters (common);
  • replace water damaged material (common);
  • diverting contaminant emissions before they can circulate in the work place;
  • storage and use of paints, adhesives, solvents, pesticides and other volatile in well ventilated areas;
  • allow time for new materials to “gas off” pollutants before occupancy;

Building renovation work using a variety of glues, varnish, paints, etc. generates large quantities of Volatile Organic Compounds (VOC). Unmanaged these VOC's can circulate through ventilation systems, stairwells, etc. effecting the occupants several floors away from the source.

All pollutant generators must be managed, and directly connected to a properly designed exhaust ventilation system, if possible, capturing the pollutant directly at source discharging the vitiated air in a safe location.  Subject to the local code, suitable air scrubbers, filtration and air cleaners can be to provided to ensure that pollutants are adequately treated, not transferred elsewhere.

Some Building management companies now require ventilation of the workplace during fitting out work to help remediate the risk of VOC's circulating in the building.

Planned Preventive Maintenance (PPM)

In many buildings IAQ can be improved by operating your existing HVAC system at its designed capacity and properly maintaining the system in accordance the manufacturers recommendations.

SBS also known as Sick buildings in Hong Kong, lack of maintenance is a problem

Frequently damaged dirty air filters, and water leakage (refer photo above) are noted creating opportunities for damp and the growth of mould - Planned Preventive Maintenance (PPM) solve IAQ problems.

The relationship between window type unitary air conditioning units and SBS is pretty common. These units don't provide filtered fresh air, therefore when used, they draw small quantities of polluted “fresh air” directly into the occupied area. If window type unitary units are the only choice, a separate filtered fresh air system is required.

E&M Design

HVAC systems must be designed, at a minimum, to meet ventilation standard defined in the local building code. However, many systems are not operated or maintained to ensure that these design ventilation rates are maintained.

Also some building codes do not actually specify a ventilation IAQ standard, therefore you will need to rely on your E&M consultant to advise during the design stage. If possible follow the ASHRAE Standard 62-1989 (with amendments) or the local equivalent.

At the time of writing, there is no regulation in Hong Kong setting the minimum fresh air requirement for commercial buildings. The exception that proves the rule, is licensed premises such as restaurants, where a miniscule 4.7 litres/sec/person is defined (50% lower than CIBSE recommended). Seven (7) litres/sec/person is the real minimum (ASHRAE states 7.5 litres/sec/person), with ten (10) litres/sec/person being optimum (noting Smoking is prohibited in Hong Kong commercial buildings). Areas with temporary or transient occupancy need careful consideration.


Although communication is the last on the list its importance cannot be underestimated. Occupants have stated, when asked, that the inability to control their work environment is a source of additional stress and tension, these in turn, may cause further problems.

If management, occupants, and maintenance freely communicate each will begin to understand the consequences of air quality complaints. Fortunately, technology has provided new solutions to these complex problems, employing web-based building interface allows more control over the local environment, reducing employee complaints, and increase workplace satisfaction.


Countless books, papers and studies have been written and performed over the past ten years yet SBS is still a widespread problem in Hong Kong, and continues to cost millions of dollars every year in lost productivity.

The problem is not insurmountable, it is not exactly rocket science, SBS problems can be solved.  In addition to improved IAQ, regular cleaning and maintenance improves plant efficiency, lowering the energy and operating costs.

Rigorous standards for building ventilation will prevent problems in the future problems.

About the author

Mr John Herbert is Managing Director at Kelcroft Consulting Engineers. He has designed, managed and engineered solutions for more than twenty years, across three continents, whilst holding a litigation free track record.


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