Pick the right air-purifier to beat the haze

SINGAPORE - With the threat of more hazy days ahead, many Singaporeans are not just arming themselves with masks but are also in the market for an air purifier.

Doctors recommend the use of such a device to cleanse air by filtering microscopic particles from it during a haze, even for those not suffering from respiratory diseases.

Closing the windows and turning on the air conditioning can help reduce the amount of particles indoors.

But this may not be enough to filter particles in the air, if the air-conditioner is not equipped with filters that can trap microscopic particles.

Dr Philip Eng, a consultant respiratory physician at Mount Elizabeth Hospital, said air purifiers are "useful for all types of individuals, especially when haze levels are very high".

He added: "The best benefit is for those with chronic heart and lung problems."

Tiny particles that get into the bloodstream can trigger potentially fatal heart attacks and strokes, while those that enter the lungs can cause symptoms like those caused by asthma, such as breathlessness, wheezing and coughing, doctors said.

Understanding Filters


Commercial air purifiers boast an array of filters in their product specifications: high efficiency particulate air (Hepa), ultraviolet (UV), photo-catalytic and carbon filters.

Mr HN Feng, senior air treatment specialist at indoor air quality company Air & Odor Management, said the different filters have varying functions, ranging from deodorising to removing bio-contaminants.

A photocatalytic filter is a new form of filtration technology that converts dangerous gases and particles into safer compounds.

Such filters and UV filters mainly target bio-contaminants - bacteria, viruses and mould.

Carbon filters are more effective at clearing odour from the air.

For times when the three-hour Pollutant Standards Index (PSI) hits record highs, as was the case two weeks ago when it hit 401, Mr Feng recommends Hepa filters, as they "can effectively capture particulate matter of 0.3 microns and above - these micro dust particles may be absorbed into a person's bloodstream".

One micron is 0.001mm. The PSI measures air concentration levels of particles that are up to 10 microns in diameter.

When shopping for an air purifier, choose one that is able to clear the most particles in the air that flows through it and has a high level of air flow through the machine. Usually, machines with high air flow contain fans which may result in them being noisier too.

The size of the air purifier is important in determining its overall effectiveness as well.

"You have to pick an air purifier that's right for the room you want to clean. Smaller air purifiers, for example, work best in bedrooms, while larger ones can be used for living rooms or small offices," said Mr Feng.

The manufacturer should specify the area capacity for which the air purifier is effective.

Two air purifiers, each of a smaller capacity, can also be used together to achieve the same effect as that of an air purifier with a larger capacity, as long as there is movement in the air, Mr Feng said.

Mind The Instructions


The air purifier should be placed in an area where air can travel freely through it, unobstructed by walls or furniture.

The air purifier can be placed at the side of a room, but with about 25cm clearance between the product and the wall, said Mr Feng.

This is a general gauge, but consumers should check their air purifier for specific instructions.

When using an air purifier, it is important to shut all doors and windows for it to work effectively, Dr Eng said.

Even then, air purifiers are not guaranteed to cleanse the air completely.

Dr Steve Yang, specialist in respiratory medicine and consultant at Raffles Internal Medicine Centre, said: "Do not assume that the air purifier will cleanse the room of every indoor pollutant.

"There will be some that cannot be removed, such as particulate and gaseous chemical compounds from cigarette smoke.

"And if the air purifier is not maintained, then the efficiency of the air cleaning device would diminish."

Air purifiers should be cleaned by changing the filters and cleaning the electrostatic collection plates every six months to remove particle build-up that might affect their efficiency.

What Tests Show


In an experiment, RazorTV (www.razor.tv), the online television service of The Straits Times, tested four air purifiers from Hitachi, Philips, Sharp and Airion.

The test involved burning two sheets of paper towels in an acrylic box which contained an air purifier and an air particle counter.

The air particle counter measured particles as small as 0.3 microns.

The paper towels were left to burn completely, with the reading on the air particle counter reaching its maximum level of 99,999,999/m³ before the air purifier was turned on for two minutes.

Readings were then recorded after the two minutes were up.

Hitachi's EP-A7000 proved to be the fastest in removing particulate matter from the air, clearing the number of particles down to 136,045/m³ in two minutes.

However, all four brands tested reduced the number of particles to a healthy level of less than one million particles per cubic metre, said qualified air quality assessor Celeste Heng, who was present to make sure the experiment was properly conducted.

Separately, the Consumer Association of Singapore (Case) tested seven air purifiers in April, focusing on the counts of specifically, bacteria, yeast and mould, all of which are hazardous to health.

It tested individually each air purifier at its highest speed in a room and measured the air quality in the room after an hour.

Case found that six measured up to the standards stated in their product specifications.

Only the performance of the F-PMF35A model from Panasonic did not match its claims, Case said.

The air purifier was advertised to be able to inhibit 99 per cent of mould, fungus and bacteria.

But the tests showed that it reduced bacteria count by about 91 per cent and the total yeast and mould count by about 78 per cent.

In a statement two weeks ago, Case said it had met Panasonic and advised the company to either withdraw or amend the claims.

The results can be found on the Case website (www.case.org.sg).

Case advised consumers to compare the prices and performance of different air purifiers before making a purchase.

RazorTV's air-filter test

RazorTV's air-filter test


Filters: Prefilter (traps larger particles), high efficiency particulate air (Hepa) filter (traps microscopic particles as small as 0.3 microns in diameter), heavy duty deodorising filter and humidifying filter

Modes: Air purify, strong deodorisation, humidify, skin moisturise and ECO (saves 23 per cent in power)

Weight: 10kg
Power consumption: 50-60Hz or 220-240W
Additional functions: Odour, dust and humidity sensors and remote control
Area capacity: 50sqm
Recommended retail price: $899


Initial particle count: 99,999,999/m³
Particle count after two minutes: 136,045/m³


Filters: Prefilter, dust collection (anti-microbial Hepa) filter and washable deodorising filter (reusable for 10 years)

Modes: Pollen, high-density plasmacluster ion shower (increases the speed of the air cleansing for 60 minutes), three fan speeds (maximum, medium and low) and automatic

Weight: 9.2kg
Power consumption: 50Hz or 220-240V
Additional functions: Odour, dust, temperature and humidity sensors Area capacity: 38sqm
Recommended retail price: $599


Initial particle count: 99,999,999/m³
Particle count after two minutes: 301,571/m³


Filters: Prefilter, nano silver filter (traps mould spores and germs), Hepa filter, five-layer photocatalyst filter (takes care of odours, volatile organic compounds, cigarette smoke, bacteria and mould spores), UV filter and carbon filter

Modes: Fan speeds from one to four, automatic/manual and sleeping mode turbo function
Weight: 10kg
Power consumption: 60Hz or 220V/120V
Additional functions: Human sensor (powers down when people are not in the room), pollutant sensor (powers down when air is clean), filter change melody, remote control, and generates vitamin anions in the air. (Vitamin anions are negative ions that are released when UV reacts with the five-layer photocatalytic filter. They attract dust to them and make the particles bigger and, hence, more easily trapped.)
Area capacity: 100sqm
Recommended retail price: $1,060


Initial particle count: 99,999,999/m³
Particle count after two minutes: 310,101/m³


Filters: Hepa filter and humidification filter

Modes: Three-step fan, automatic and timer

Weight: 10kg
Power consumption: 50Hz, 20W or 220-240V
Additional functions: Air quality light indicators and dual sensors Area capacity: 40sqm
Recommended retail price: $1,009


Initial particle count: 99,999,999/m³
Particle count after two minutes: 246,761/m³


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