The Hazards of Noise Pollution in Cleanrooms

  It is universally known that particle control is the core concern of cleanrooms and countries and organizations all over the world have been formulating and updating regulations and standards on cleanrooms. In modern times however, due to the emerging of terms like sub-health, Workplace Safety, EHS (Environment Health Safety), the long forgotten noise control draws higher and higher attention and governments in the world have stepped up efforts to address the noise pollution.

Adverse Effects of Noise Pollution  
  Reduced work performance and efficiency: high noise level in cleanroom or in workplace will make the staff unable to concentrate or communicate with each other. As a result, the working atmosphere and performance will worsen. A study shows that employees are about 60% less productive in a loud or noisy environment than those working in a less noisy workplace.

  Hearing damage and other medical conditions: Noise pollution can adversely and severely affect the work and lives of billions of people. Researches have shown that there are direct relations between noise and health, such as the direct consequential illness like hearing loss, high blood pressure, speech interference, lost productivity and other stress-related illnesses. In addition, long-term or constant exposure to high levels of noise can lead to countless health issues.

Regulations Concerning Noise Control  
  Over the century, noise control in cleanroom or workplace in at large has been brought to attention and regulations have been evolving to adapt to the increasing demands. 

  US Federal Standard 209A was developed in 1966 and 209B was revised in 1974 stipulating: “The control of noise of cleanrooms are carried out to meet operational or product requirements, and to keep employees working in a comfortable and safe environment.”. 

  The Control of Noise at Work Regulations 2005 issued by the UK government specifies that “The employer shall ensure that risk from the exposure of his employees to noise is either eliminated at source or, where this is not reasonably practicable, reduced to as low a level as is reasonably practicable.” 

  ISO 14644-4 (draft version) standard regulates that: “An appropriate sound pressure level should be selected according to the requirements of the comfort and safety of workers in the cleanroom and sound reflection.”

  According to GB50457-2008: Code for Design of Pharmaceutical Industry Cleanroom, “The noise level (as-built state) in the clean room should not exceed 60dB(A) for non-unidirectional flow clean rooms, while noise level should not exceed 65dB(A) for unidirectional flow cleanroom”

  As a matter of fact, the baseline noise levels 65dB(A) and 60dB(A) have been widely applied to the cleanroom design and construction. In addition, as the noise control regulations get stricter and developing, many European countries are applying noise control regulations for workplace to cleanroom. Cleanroom is a type of workplace after all. 

How to control noise level in cleanroom?  
  In countless workplaces there are already protection measures again noises, such as ear plugs or reducing-noise headphones, arrangements of silent booths. On the other hand, the best way to reduce noise level is to lower it from the source.

  Selection of low-noise equipment: the most effective way to reduce noises is to choose equipment that generates the least noises. Fan filter units (FFU), the core element of modular cleanroom, come in direct contact with the interior of cleanroom, generating the highest noises in the cleanroom. Moreover, the higher the cleanliness, the more FFUs and the higher the noises in cleanroom. Therefore, it is critical to install FFUs that produce less noises. 

  Tests show that the FFUs with EC motor can generate up to 40% less noises than those with AC motor. As the core component of modular cleanroom, once the noises of FFUs are reduced, the overall noise level of the modular cleanroom will drop dramatically. 

  Isolation of noise transmission: another effective way to reduce noises is to cut off the noise transmission. Rockwool sandwich panels, for example, boast sound isolation capacity of about 35dB(A), making them ideal wall materials for the modular cleanroom. By utilization of such wall panels, the outside noises can be effectively isolated. 

  Along the HVAC system, multiple measures can be taken to lower the noises. The static-pressure box (or plenum box) can be replaced with silent box with sound insulation rubber placed to the inner surface. This would greatly decrease the noises. Furthermore, canvas soft joint can be applied to reduce vibration of the air duct system, thus diminishing the noises to the greatest extent. 

  Sound isolation rubbers are also widely applied in order to minimize the noises. It happens a lot that the production equipment in the cleanroom generates great noises (for example, generally motor and transformer hum at frequencies near 30, 60, and 120 Hz). This is where the silent booth comes in. More and more factories build silent booth to enclose the equipment where the highest noises comes out, to reduce the noises sharply.

  Particulate matters and micro-organisms have always been the center of cleanroom. In recent years however, more attention has been focused on the noise reduction and energy conservation. It is predicable that noise control will soon become a major parameter to be considered at the outset of cleanroom design and construction.