Noise pollution: Will Dhaka ever be quiet?

The noise pollution in Dhaka decreased significantly during the initial days of the Covid-19-induced lockdown period. However, the brief interlude of quiet has faded since restrictions were lifted in September.

In the last two months of 2020, noise pollution levels in the capital increased by an alarming average of 10% year-on-year, posing a serious health risk to residents, according to a recent study.

Impulsive noise (noise that lasts for a short duration) increased by 10-12%. Compared to 2019, continuous noise (noise that lasts for a longer duration) declined by 3-4% as per the study conducted in November and December last year.

In addition, the study found 15% less traffic on the city's roads compared to 2019.

The use of banned hydraulic horns has risen by 15-25% on the city's roads, according to the study carried out by the Centre for Atmospheric Pollution Studies (CAPS) of Stamford University. The horns account for a major portion of impulsive noise in the city.

Dr Ahmad Kamruzzaman Majumder, CAPS founder and director, said: "The most alarming thing is that the situation will deteriorate further if the number of vehicles go up to pre-Covid period levels."

He said most impulsive noise in the city is induced by hydraulic horns, and continuous noise is induced by motorized machines such as generators.

Sound levels above 70 decibels (dB) is considered an extreme level by the World Health Organization (WHO). However, the study found that high 120-129 dB sounds are  recorded in several places across Dhaka city, said Dr Majumder, also chairman of the environmental science department of the university.

Women, children, pregnant women and traffic police are affected the most by shrill sounds as they expose serious threats to mental health, he added.

He said 8% of traffic police are at risk of permanent hearing loss, while 35% are suffering from temporary hearing problems due to acute noise pollution.

As per the Noise Pollution (Control) Rules 2006, the permissible sound level for Bangladesh is 50 dB for the daytime and 40 dB during the night in quiet areas.

In residential areas, the permissible limit is 55 dB for daytime and 45 dB during the night, while it's 60 dB for the daytime and 50 dB during the night in mixed areas (residential, commercial and industrial localities) and 70 dB for daytime and 60 dB for the night in commercial areas. 

The WHO considers 0-20 dB as a normal sound level, 21-40 dB as a moderate sound level, 41-70 dB as a mild sound level, 71-90 as an extreme sound level and 91-120 as an intolerable sound level. The maximum permissible exposure time at 85 dB is 8 hours, at 100 dB it is 15 minutes, at 110 dB it is one minute and at 120 dB it is only nine seconds, according to the WHO. 

If more than 100 dB sound is exposed to anyone for a 15-minute period of time, it could result in temporary hearing loss. A 120 dB sound could result in permanent hearing loss.

Experts say sound pollution causes mental and physical illness among people. It can cause high blood pressure, headaches, indigestion, ulcers, and also affects sleep.

Talking about another recent study conducted in the Bangladesh Secretariat areas, Prof Majumder said the noise pollution increased in the area even after it was declared as a no horn zone a year ago.

The researchers measured sound levels at 12 surrounding points of the Secretariat. The highest 128.2 dB sound was recorded at the Press Club point, where the highest 126.1 dB sound was also recorded in the 2019 study. 

Sound levels above 70 dB (shrill sounds) lasted on average for 91.99% of the  time at the 12 points. Amongst these locations, extreme sounds lasted for 100% of the time at Paltan bus stand, 99.4% of the time at Zero point and 99.2% of the time at Kadam Foara point.