What HDB didn’t tell you about Punggol (and Pasir Gudang)

[Updated – 21/3/2019]

On 6th March 2019, it was announced that Pasir Gudang had been hit by a chemical spill incident, affecting around 2,775 people in the area and forcing 111 schools in the Johor region to shut down. According to Malaysian authorities, this was caused by “toxic waste” illegally dumped into a river – although details still remain unclear. Malaysia’s Department of Environment also lacks “concrete statistics“, but there could be as many as 46 more sources of pollution, beyond the identified dumping site. The Malaysian government has not declared a national emergency at this time.

In a Straits Times article on March 18 , it was reported that a hazardous materials response team that carried out tests on samples after the incident had found the presence of Benzene, Tuolene, Xylene, Ethylbenzene and D-limonene.

According to the World Health Organization (WHO), “benzene is carcinogenic to humans, and no safe level of exposure can be recommended”.

Singapore authorities say that they are continuing to monitor the situation. According to a joint statement released by NEA, AVA, PUB, and SCDF on March 19, air and water quality in Singapore remain unaffected by the event and that “ambient levels of volatile organic compounds (VOC), including benzene, measured at the VOC monitoring stations in the North-eastern region, remain within safe levels”. PUB also stated that “The water quality of our inland waterways and reservoirs in north and north-eastern Singapore is also unaffected”.


With Singaporeans oversubscribing the Punggol HDB projects in the Aug 2018 BTO sales launch, it would seem that the two main concerns about living in the North-eastern tip of Singapore — namely the bad traffic conditions to the CBD and the air pollution from Pasir Gudang petrochemical complex across the Straits of Johor — have been put aside. In this article, we take an in-depth look at Pasir Gudang, to find out what we haven’t been told about the petrochemical hub.

[Note: An earlier version of the article misinterpreted the odds equivalent of a 10−4, 10−5 and 10−6 increase in probability, overstating it by a factor of 10. 10−5 should equate to 1 in 100,000 odds (1/100,000), not 1 in 10,000 (1/10,000). We apologise for the error, which has since been corrected.]


For those who don’t know yet, Pasir Gudang is an industrial district in Johor, Malaysia with a large concentration of petrochemical industries such as refineries (similar to Singapore’s Jurong Island). The zone dedicated to heavy industries is about 20 square kilometres (sq km) in current size, larger than the areas of Punggol and Sengkang combined (16.5 sq km).

Using Google Maps, we ascertained the distance between the Punggol Point Cove and Punggol Point Woods BTO projects to be about 2.5 to 3km from Pasir Gudang factories closest to the Malaysian shore. Previous BTO projects such as Northshore Cove (Feb 2017 launch) are situated even nearer to Pasir Gudang’s petrochemical plants. Johor Port, where hazardous petrochemical products are shipped to and from Pasir Gudang, is located directly opposite Punggol Point Jetty (the tip of Punggol) and just over 1km away.

Pasir Gudang sits in the shadow of HDB’s latest housing projects. Credit: Herman Wu

Something in the air

Because of the concentration of petrochemical activities in Pasir Gudang, Singaporeans living in the north-east have at various times reported “chemical smells”. What they are smelling is actually a mixture of sulfur dioxide and volatile organic compounds (VOCs). The odour can be acrid and gas-like, and residents — some from as far as Ang Mo Kio due to north-easterly prevailing winds — have reported experiencing headaches, eye irritation, itchy throat and other respiratory conditions that correspond to symptoms experienced during and after exposure to airborne chemicals. Exposure to airborne VOCs has also been known to trigger asthma attacks in sufferers.

And no, these reactions aren’t psychological. A 2015 Detailed Environmental Impact Assessment by Lotte Chemical Titan, which operates one of the largest petrochemical facilities in Pasir Gudang, found that the measured values of some VOCs within the plant’s premises exceeded “odour threshold values”, owing to the large number of similar oleochemical plants in the area. During the inter-monsoon months and the Northeast Monsoon (October through to May every year), prevailing winds from the north means that Punggol residents are directly subject to the odour of the higher-than-threshold VOCs from Pasir Gudang, the health impact of which we’ll further examine later.

Hourly variation of surface wind speed (m/s) and direction for each month (1981-2010 average). Credit: weather.gov.sg

Petrochemical plants also frequently perform “flaring”, the controlled burning of waste gasses generated during the petrochemical production process. For Punggol residents, blazing flames from chimneys lighting up the night sky and faint roars from the chimney stacks are common sights and sounds. The by-products of flaring — large amounts of carbon dioxide — do not necessarily pose an immediate health hazard, although residents are probably witnessing global warming in motion.

What the Singapore government says

Airborne VOCs in high enough concentrations can be toxic to humans who inhale them. Although Singaporeans affected by the stench have repeatedly expressed their worry that the gases might be harmful to health, the Singapore National Environment Agency (NEA) has so far dismissed any reason for alarm. For the chemical smell reported in September 2017, the NEA assured the public that its air monitoring stations “detected only low and safe levels of volatile organic compounds (VOCs)” that are “well within international safety guidelines”. No figures were given, nor were the safety guidelines elaborated upon.

The need for facts and figures

The concern about Pasir Gudang, beyond physical irritations, is the potential for the VOCs to cause long-term damage to the health of residents of Punggol (who are literally on the front-line should an accident or major incident happen in Pasir Gudang). Going back to the incident in September 2017, the source of the more intense than usual chemical smell was traced to a fire at a Lotte Chemical Titan facility at Pasir Gudang (see below video of fire). The petrochemical giant was subsequently issued a stop-work order by the Malaysian authorities for the incident, but not before afflicting millions of Singaporeans with chemical fumes that was released during the incident.

Such incidents, which trigger a larger than normal release of VOCs to the atmosphere, is commonly called an “emission event” in industry-speak. According to an industry insider we spoke to, these “emission events” are common (they don’t necessary have to involve fires). In Texas, USA, the emission events reported in 2010 accounted for about 15% of VOCs and sulfur dioxide released that year, from across the state’s refineries, chemical plants, and natural gas facilities.

So, we felt it was necessary to delve into scientific research to ascertain the effects of living in the shadow of Pasir Gudang, for Punggol residents and also for all Singaporeans. From computational simulations to real-world studies, our findings were a revelation.

But first, what are VOCs made up of?

If you’ve ever visited a petrol station and smelled petrol, you’re effectively inhaling VOCs*. VOCs easily turn into vapour state, and what is widely-regarded as the most harmful component of petrochemical VOCs is benzene, along with toluene and xylene. The three VOCs are known as BTX; there are several BTX producing facilities in Pasir Gudang, and Lotte Chemical Titan has began operations at a new BTX plant in 2018 as part of its latest expansion, producing 134,000 tonnes of BTX a year.

According to the World Health Organization (WHO), “benzene is carcinogenic to humans, and no safe level of exposure can be recommended”. (Carcinogenic means that a compound or substance may cause cancer in humans.) As airborne particles, the WHO states that, as a guide, the concentrations of benzene associated with an excess lifetime risk of leukaemia of 10−4, 10−5 and 10−6 are 17, 1.7 and 0.17 μg/m3, respectively, where μg refers to microgram (1 gram = 1000000 microgram).

Put it another way, a constant exposure to 17 μg/mof airborne benzene will give you an additional 1/10,000 chance of getting leukaemia, a cancer of the blood. An constant exposure to 1.7 μg/m3 of airborne benzene, on the other hand, will give you an additional 1/100,000 chance of getting leukaemia. The odds of 1/10,000 is the chance of striking a 1st prize in 4D with a matching number, whereas 1/100,000 is roughly the odds of being struck and killed by lightning in your lifetime.

While the chances of getting leukaemia due to benzene in VOCs can be expressed in terms of striking lottery or meeting with an unlikely accident in your lifetime, a more accurate example would be expressing it in terms of population. For a town of 200,000 population that has a 1.7 μg/m3 concentration of airborne benzene on average, it is estimated that about two more people in that population will develop leukaemia in their lifetimes (i.e. two people + a baseline figure).

For Punggol residents, the amount of airborne benzene the town receives will likely determine the odds of the leukaemia lottery among the town’s unwilling participants. The town currently has about 150,000 residents, and the figure is set to double in a decade’s time.

*Scientific studies conclusively show that petrol station workers have a marked increase in risk of cancer.

Finding a mini Punggol and Pasir Gudang… in Sweden

But first, without any figures from NEA, we need to find out how much benzene is actually found in the air in a similar real-world situation to Punggol, with an example that is as close to Punggol and Pasir Gudang as possible.

That first lead us to the south-western part of Sweden. Like Punggol, Ödsmål is a town — albeit a low-rise one — located 3km downwind from a petrochemical industrial area totalling about 2.5 sq km.

“Exposed areas”: three areas (North, Central, and South) in the municipality of Stenungsund and the municipality of Odsmal, 3 km north of Stenungsund in the direction of the prevailing winds from the industrial sites. The black areas represent the location of the petrochemical plants. Residential areas are marked with pink colour. Reference: Int J Environ Res Public Health. 2013 Apr; 10(4): 1418–1438.

The experiment: In 2006 and 2007, a group of researchers — paper in Swedish but we got it translated for our own understanding — measured the level of common VOCs in Ödsmål throughout the year using portable ground level apparatus. (It must be noted that average wind speeds in Ödsmål is about twice the speed of winds experienced in Singapore.)

What was found: The average annual mean of airborne benzene recorded in Ödsmål is 0.77 μg/m3. Toluene and xylene were not measured. With exposure to this concentration to airborne benzene, we estimate that at least 1 person out of about every 250,000 in the population would develop leukaemia in their lifetimes. Given that the population of Ödsmål is only a little over 600, it would seem that they have nothing much to worry about.

However, the most concerning thing we found here isn’t the amount of airborne benzene detected, but the fact that the researchers had found benzene levels to be abnormally high in Ödsmål in January 2007. In this particular month, several elevated concentrations (11 to 58 μg/m3) of airborne benzene were detected. Lasting for a few hours each time, the researchers traced the elevated concentrations, or emission events, to an incident where two major petrochemical facilities nearby had lost power.

Typically, when a petrochemical facility experiences a power failure and has to start up again, large amounts of VOCs are released into the air. We can only hope that Pasir Gudang’s power grid is as good as ours, although power outages there have indeed happened a few times over the past years (many of which aren’t reported and remain unknown to the authorities).

The differences between Ödsmål and Punggol:

What does it mean for Punggol?
While we cannot draw a direct parallel between the two towns, we know for sure that petrochemical facilities do indeed have an impact on neighbouring communities, especially in instances of emission events. In fact, in a separate 2013 study on Ödsmål residents, over 4 in 10 expressed worry about the health effects of industrial pollution in their area, compared to 1 in 10 from a control group. It’d be interesting to see a similar survey on Punggol residents, compared to those living in the rest of Singapore.

A worst-case scenario through the lens of Ulsan

The city of Ulsan in South Korea.

Sometimes, computer simulations can paint more useful scenarios than simply observing the real-world. Wanting to know how VOCs would be dispersed over a radius, a group of Korean researchers applied advanced computer modelling tools to the city of Ulsan. Their objective was to use real-world data, including myriad weather data and data from past accidents, to “assess the risk caused by an accidental release and dispersion of the toxic chemical benzene in the vicinity of a highly populated urban area”. 

The researchers assumed the source of the accidental emission of benzene to be located at the center of the Ulsan Petrochemical Industrial Complex, which is within 3–5 km of heavily populated downtown Ulsan (about the distance between Pasir Gudang and Punggol Central).

The experiment: Benzene is simulated to have been released from a tank 3 metres in diameter and 5 metres in height at an emission rate of 94 grams per second. The simulated release of benzene was done at two timings, one at 1pm local time, and the other at 1am local time.

Without diving into complex mathematical equations, this was how the study was executed: the simulator ran the data from five consecutive August summer months* (from 2009 to 2013). A set of 155 simulations (31 days over 5 years) were conducted to derive the 1-hour average ground-level benzene concentrations for each case, which were then averaged to determine the mean August concentration for a given day.

*Ulsan’s average daytime and nighttime wind speeds are identical to Singapore’s, although max daytime wind speeds in Ulsan are about 20% higher.

What was found: For us laymen, there were two surprising discoveries. Wind does play a huge part, but not in the way we had expected. First, the study found that a higher wind speed resulted in a smaller radius of dispersion of airborne benzene, whereas a lower wind speed resulted in a larger radius of airborne benzene dispersion. This is because a higher wind speed doesn’t allow the benzene plume to rise high into the atmosphere and disperse further, contradicting our earlier assumption that the reverse was true.

In the daytime in particular, the smaller radius of dispersion of airborne benzene at higher wind speeds also means that the “high concentration region” of airborne benzene (46 μg/m3) is confined within a smaller radius of the source (1.2km in the study). This is good news for Punggol residents, but only in the day. For Pasir Gudang, a slower northernly wind — which is most common at night — is more likely to transport the high concentration of airborne benzene to Punggol and extend the total impact or airborne benzene further inland. This is made worse by the fact that rising heat given off by buildings at night help airborne benzene travel further — the second discovery that took us by surprise.

Here’s a visual representation of the difference between day and night in Ulsan’s case. (The largest circle denotes a 10km from the source; inner circles denote 5km, 3km, 2km and 1km.)

Comparison between the average and highest 1-hour benzene concentration obtained from the multiple simulations conducted in August 2009–2013. (a) and (b) illustrate the average distributions for the daytime (1300 LST) and the nighttime (0100 LST), respectively. (c) and (d) are the same as (a) and (b), but illustrate the highest concentrations. Reference: Atmospheric Environment Volume 144, November 2016, Pages 146-159

What does it mean for Punggol?
Well, scratch that. How about what does it mean for Singapore? We say this because anything bad that happens in Pasir Gudang will, over the course of 24 hours, likely affect vast areas of Singapore, especially given these three “perfect storm” combination of factors that count against us: wind from the North; wind speeds dipping at night; heat rising from buildings in Punggol, all of which increases the radius of airborne benzene dispersion. Bam! So, while Punggol (and Sengkang) residents might feel the maximum wrath of benzene in the nighttime given a worst-case scenario (like the fire at Lotte Chemical Titan), it’s likely they won’t be the only ones choking.

[Recommended article: ‘Massive’ Covid-19 cluster sparks Punggol HDB residents’ worst fears]

So… will Pasir Gudang kill us?

Well, a multiyear Taiwan study published in 2006 might give us a bit of definitive clarity as to which group of people stands to be most affected by living near petrochemical industries.

The experiment: To explore the relationship between residential petrochemical exposure and risk of leukemia, the Taiwanese researchers conducted a study in four areas with petrochemical plants. The researchers defined the four areas as “potentially exposed areas” that were within a 3km radius of any of the four petrochemical complexes. The subjects of the study were residents who lived in these potentially exposed areas, as well as residents from elsewhere who formed a control group. Each resident was assigned a “residential petrochemical exposure” factor (i.e. risk factor) depending on the following:

What was found: Among study participants under the age of 20, there was no link between increasing residential petrochemical exposure and risk of leukaemia. Among study participants between the ages of 20 and 29, however, increasing residential petrochemical exposure was positively associated with the risk of leukaemia.

The researchers concluded that higher levels of residential petrochemical exposure appeared to elevate the risk of developing leukaemia among individuals between the ages of 20 and 29 years, but did not appear to affect risk among children.

In another Taiwanese study published in March 2018, researchers found that “elderly and female residents living within 10 km of a petrochemical complex had higher carcinogenic exposure and cancers than those living farther away from the complex after the complex had been operating for 10 years”. The study also highlighted other potentially carcinogenic pollutants other than benzene, such as heavy metals. (FYI: 10km from Pasir Gudang would include the whole of Hougang, almost all of Ang Mo Kio and parts of Serangoon.)

Are there any other studies that show no ill effects of living near a petrochemical complex, then?

We did try to find “no effect” studies, but these seemed few and far between. A 1999 UK study did find that there was no significant increase in the risk of leukaemia within 2 km or 7.5 km of seven petrochemical sites locally. It did, however, find a weak link between the risk of Hodgkin’s disease and proximity to major petrochemical industry.

But bear in mind that none of these findings would matter if…

Because your benzene and VOCs exposure would’ve eclipsed anything Pasir Gudang can throw at you.

Wall paints in their liquid state typically give off a high amount of VOCs.


What HDB and the Singapore government should tell us

Given the continued commitment of the Singapore government to develop Punggol and the North-east as an ideal place for Singaporeans to live, work and play, our relevant authorities cannot afford to indulge in inaction, operate with fear (of knowing the truth), and serve existing and future residents without accountability to Pasir Gudang’s impact on the town.

Bear in mind that we’re not asking for answers right away, but a promise to the people that there would be some concerted initiative and effort in seeking, and most importantly sharing, more knowledge. The longer we wait to be transparent (e.g. about the numerical concentration of airborne VOCs in the North-east), the more our leadership risks losing all accountability down the road.

And when it comes to more in-depth studies of Pasir Gudang’s impact on Punggol residents and the broader public, one thing’s for sure: Singapore’s universities and research bodies certainly don’t lack any expertise. Studies that have been done in other countries and cities, the ones highlighted in this article, can and should be done in Singapore to ascertain our situation and risks.

Even if the possibility of something bad happening to a resident is as low as winning 4D 1st prize (or as high, depending on how you see it) or as likely as being struck by lightning, Singaporeans still deserve to know.

Photo taken from TODAY. The Malaysian Insight file photo

In light of this recent event, a comprehensive and transparent studies of atmospheric VOCs in Punggol from the government will go a long way in assuaging our fears and reaffirming our trust in the authorities. Anything less, and Punggol will always be an estate that’s more hype than substance, more risk than reward.

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