Smoke Haze

Effect of Smoke Haze

 

The main pollutant of concern to health during a smoke haze is the fine particulate matter or PM10 (particulate of size 10 micron and below). The health effect depends on the severity of the smoke haze as described by the PSI (Pollutant Standards Index) reading. At a PSI of 101 and above, the air quality is deemed unhealthy.

During a smoke haze, the fine particulates enter an air-conditioned building through the fresh air intake and by infiltration through openings and gaps. The particulate levels indoor can thus build up to unacceptable levels. This could have undesirable health effect on the occupants of the building and adversely affect the efficiency of the air-conditioning system.

 1) What is PSI?

How is the index measured?

PSI stands for 'Pollutant Standards Index'. It is an index developed by the United States Environmental Protection Agency (USEPA) to provide accurate, timely and easily understandable information about daily levels of air pollution.

The ambient air in Singapore is monitored through a telemetric network of  air monitoring stations strategically located in different parts of Singapore.

Air pollutants such as sulphur dioxide, nitrogen dioxide, ozone, carbon monoxide and particulate matter called PM10 (particulate matter of 10 microns or smaller in size) are used in the determination of the index.

The PSI value gives an indication of the air quality as shown:

PSI Value	PSI Descriptor
0 to 50	Good
51 - 100	Moderate
101 - 200	Unhealthy
201 - 300	Very unhealthy
Above 300	Hazardous

 

2) How will NEA issue health advisories during times of poor air quality?

Health advisories pegged to PSI and PM2.5 are tabulated below. NEA will issue advisories based on either the PSI or PM2.5, whichever is more stringent.

Health Advisories Pegged to PSI

PSI Value	Health Advisory
0 to 50 (Good)	None for the general population
51 to 100 (Moderate)	None for the general population
101 to 200 (Unhealthy)	Persons with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. The general population should reduce vigorous outdoor activity.
201 to 300 (Very unhealthy)	Elderly and persons with existing heart or lung disease should stay indoors and reduce physical exertion and outdoor activity. The general population should avoid vigorous outdoor activity.
301 to 400 (Hazardous)	Children, elderly and persons with existing diseases should stay indoors and avoid outdoor activity. The general population should avoid unnecessary outdoor activity.
> 400 (Hazardous)	Children, elderly and persons with existing diseases should stay indoors, keeping the windows and doors closed and avoiding physical exertion as far as possible   Outdoor activity should be avoided. The general population should keep physical exertion and outdoor activity to as low a level as possible.

 

Health Advisories Pegged to PM_2.5

24-hr PM2.5 concentration (µg/m3)	Health Advisory
0 to 15	None
>15 to 40	None for the general population. Unusually sensitive people should consider reducing prolonged or heavy exertion.
> 40 to 65	Following groups should reduce prolonged or heavy outdoor exertion: People with heart or lung disease Children and older adults Everyone else should limit prolonged or heavy exertion.
> 65 to 150	Following groups should avoid all physical activity outdoors: People with heart or lung disease Children and older adults Everyone else should avoid prolonged or heavy exertion.
3) Under what circumstances do we need to wear mask and what are the advisories on the use of mask? When the 24-h PSI level exceeds 150 in the 'Unhealthy' range, people with existing heart or respiratory ailments or those who are more susceptible to smoke haze are advised to wear a respiratory mask when they go outdoor. People with respiratory ailments are however, advised to consult their doctors on the use of respirator masks. Respiratory masks, such as N95 masks, are designed to keep out fine particulate matter and hence, protect the wearers from breathing in the smoke haze particles in the air. The mask should be changed when it gets soiled or distorted in shape. Surgical masks and paper masks do not provide adequate protection from the haze particles.
Air Cleaning Devices for Buildings (with Central Air-Conditioning System) For buildings with central air conditioning systems, air cleaning devices can be fitted so that the particulate level in the indoor air can be kept within acceptable levels during a prolonged smoke haze period. The devices include electrostatic precipitators and media filters. Electrostatic precipitators operate by electrically charging dust particles as they pass a set of electrodes. The charged particles are subsequently collected by charged collector plates (with an opposite charge) downstream of the charging electrodes. They have minimal effect on airflow. Media Filters are mats of fine fibres oriented perpendicular to the direction of airflow. Particulates are intercepted and trapped in the fibres. They are available in a wide range of capture efficiencies. For smoke haze, filters manufactured for more efficient removal of fine particulate should be used. The conventional medium to high efficiency media filters that can trap fine particulate are typically dense and may hinder air flow if the fans are not designed to match them. There is another type of medium efficiency filter that is less dense and therefore exerts a lower resistance to air flow. This type of filter contains electrostatically charged fibres that attract and retain fine particles. The capital and operating costs vary depending on the particular type of air cleaning devices selected and the design of the air-conditioning system. Based on NEA's assessment, the overall annual cost range from $2,000 to $10,000 for a floor area of 1,300 sq.m. The costs are for an assumed haze period of three months per year. The actual costs of the options will need to be ascertained with system suppliers.

Portable Air Cleaners

Portable air cleaners are compact, stand-alone appliances designed to keep the particulate levels of an enclosed space low.

Several models of air cleaners have been found to be able to reduce the level of fine particles in a typical bedroom to an acceptable level during a smoke haze.

In general, there are three main types of air cleaners available in the market. They are:

a) Ionisers which impart negative charge to the particles that subsequently stick to surrounding surfaces or are filtered out;

b) Electronic air cleaners which removes particles by electrostatic precipitation; and

c) High Efficiency Particulate Absolute or HEPA air cleaners which removes particles by mechanical filtration and diffusion.