NIOSH Sound Level Meter Mobile Application

The NIOSH Sound Level Meter is a free mobile technology application (app) for smart phones or tablets that measures occupational exposure to noise.  

Description:

The National Institute for Occupational Safety and Health (NIOSH) has developed a Sound Level Meter (SLM) for iPhones that can be used to measure occupational exposure to noise. The NIOSH SLM was conceptualized after studies found that many other free smartphone apps that measure noise exposure are not uniformly accurate (Kardous & Shaw, 2014). Although the NIOSH SLM is not intended to be used for compliance purposes or to replace a professional sound level meter, it is an accessible and reliable way to determine if workers may be overexposed to noise on the job.

The NIOSH SLM has a variety of functions depending on the user’s goal.  It can measure A, C, or Z-weighted decibels instantaneously. A-weighting is used most frequently for occupational purposes, as it weights different frequencies to more closely match their impact on hearing.

The NIOSH SLM also provides an “average” decibel level (LAeq) over any given period of time. This measurement can be used to calculate a user’s daily percentage dose based on OSHA or NIOSH hearing loss criteria. All saved information can be uploaded or sent to other recipients via email. Although a calibrated external microphone is recommended, it is not required.

Risks Addressed:

Repeated overexposure to noise causes permanent hearing loss and ringing in the ears (tinnitus).  It has also been associated with hypertension and other cardiovascular diseases (Girard et al, 2015).

The Occupational Safety and Health Administration (OSHA) requires that workers’ 8-hour LAeq remain under 90 decibels, while NIOSH has recommended that it remain under 85 decibels. Although NIOSH’s recommendations are not legally enforceable, they are more protective and preferred for maximum hearing conservation. Table 1 shows how long a worker can safely be exposed to different levels of noise (measured in A-weighted decibels, or dBA) according to both OSHA and NIOSH criteria.

 

dBA

OSHA

NIOSH

80

32 hours

25.4 hrs

85

16 hours

8 hours

90

8 hours

2.5 hours

95

4 hours

47.6 minutes

100

2 hours

15 minutes

105

1 hour

4.7 minutes

110

30 minutes

1.5 minutes

115

15 minutes

28 seconds

120

7.5 minutes

9 seconds

125

3.8 minutes

3 seconds

Table 1

How Risks are Reduced:

Accurately measuring the noise level of a tool or work environment is a critical first step in reducing the burden of occupational hearing loss. The decibel scale is logarithmic, not linear, meaning that going up 20 decibels is equivalent to a 100-fold increase in sound power level. However, the human ear is not very good at detecting these changes. Although going up 30 decibels is equivalent to a 1000-fold increase, most people only register this as an 8-fold increase.

Using the NIOSH SLM, tools or processes that are found to be consistently louder than 85 dBA can be identified. These tools or processes can then be replaced with similar, quieter alternatives. If substitution is not practical, workers can be isolated from the source of the noise with sound barriers, or administrative controls can be used to limit the amount of time each individual worker spends in a noisy area.

NIOSH recommends keeping workers' daily exposure below 85 dBA over an 8-hour average. When workers are exposed to noise levels at or above 85 dBA, employers need to protect workers from hearing loss - a fundamental requirement of OSHA regulations. Before using personal protective equipment like earplugs, OSHA requires that other types of controls be considered first - like using less noisy equipment or limiting worker exposure to noise. Often the best way to protect workers from workplace noise is to purchase and use quieter equipment. Not only can ‘buying quiet’ (see Buy Quiet solution) better ensure worker protection from noise but creating a quieter workplace can negate the need for a hearing conservation program.

When engineering or administrative controls are not practical, workers must be given hearing protection devices. Although all hearing protectors are assigned a Noise Reduction Rating (NRR), most workers do not receive the labeled amount of noise reduction (Murphy et al, 2013). The best way to determine hearing protector effectiveness is to perform fit testing, which uses a computer program and special headphones to gauge the actual noise attenuation of hearing protectors worn by workers.

Regardless of how you measure effectiveness, an essential element in using hearing protectors is proper training. Untrained workers are much less likely to wear their hearing protectors correctly, possibly rendering them useless. Untrained workers are also less likely wear hearing protectors in the first place.

When training workers it is important to keep in mind these basics: 

  • Provide on-the-job training before exposure to noise and at regular intervals.
  • Ensure that workers understand both the short-term and long-term hazards of noise.
  • Show workers how to use hearing protectors correctly.
  • Have workers demonstrate that they can insert hearing protectors correctly.

Additional Considerations:

The NIOSH SLM is currently available for iPhone only due to variability in the quality and accuracy of Android internal microphones. For even more accurate readings on your iPhone, use a calibrated external microphone.

Exposure to certain medications, solvents, and pesticides can also cause hearing loss. These ototoxic chemicals may have an interactive or synergistic effect with chronic noise exposure, accelerating hearing loss. Potential exposure to these ototoxic chemicals must be addressed in your workplace’s hearing conservation program. 

 

Contributors:

Sara Brooks, MPH, CPH - CPWR The Center for Construction Research and Training
Lt. Bryan Beamer, PhD, PE, CSP - The National Institute for Occupational Safety and Health