Posts Tagged ‘OSHA’

Sound and Exposure Standards

Sunday, November 14th, 2010

     How many crickets clicking their legs together in unison would it take before we would suffer hearing loss at the sound exposure? Would we need to sit in a garden filled with millions of them all night long, only to discover in the morning that we could no longer hear the tea kettle’s whistle? The chart below may not provide the answer to this question, but it does provide some very good examples of different sounds and the point at which they become hazardous.

     So how do we know where we’re at safety-wise with sound pressure levels and exposure times? This question wasn’t pondered until the 1950s, when the military, specifically the Air Force, provided the first standards in this regard in 1956. This initial action was followed up by numerous studies and standards committees wrestling with the issue. It wasn’t until 1981 that the Occupational Health and Safety Administration (OSHA) required employers to implement hearing conservation programs for employees in certain noise-filled environments.

     What surprised many of the first scientists studying the impact of sound is that sounds don’t necessarily have to be initially perceived as “too loud” in order to cause hearing loss. Many sounds that we perceive as easily tolerated can in fact cause hearing damage if exposure is long enough.

     So what’s “long enough?” Title 29 of the Code of Federal Regulations, Section 1910.95, lists the OSHA permissible sound exposure durations at various sound levels, as shown in Table 1.

Duration of Exposure (Hrs.) Sound Level (dB)
8 90
6 92
4 95
3 97
2 100
1.5 102
1 105
0.5 110
0.25 or less 115

Table 1 – OSHA Permissible Noise Exposures

     Just to put things into perspective, a small chain saw tearing into a log typically produces sound at 90dB, or 90 decibels, which you will recall from last week’s article is the measuring unit used for sound. And that noisy truck clattering down your street, the one that your dog can’t help but bark at, can produce 100dB. The guy standing on the airport tarmac directing your plane into the gate can be exposed to as much as 150dB. There’s a good reason he’s wearing ear protection.

     Let’s take a closer look at the information provided in Table 1. It states that you most likely will not suffer hearing loss if you spend up to 8 hours in a place where the sound level does not exceed 90dB. Comparing that information to Table 2, which is specific to noises produced at a power plant, we see that this sound level is produced by the typical steam turbine.

     One thing to keep in mind is that when we are exposed to various sounds throughout the day, we can compute a time-weighted average noise, or TWAN, to help us determine if our overall environment poses a threat to our hearing. This method of assessing the gross impact of many different sound exposures is represented by the formula:

TWAN = (C1 ÷ T1) + (C2 ÷ T2) + (C3 ÷ T3) + …

where C represents the total time of exposure at a measured sound level, and T represents the total time of exposure. T, which in our example stands for “hours,” is found in the left column of Table 1. Based on scientific studies of sound’s effects on the human ear, if the TWAN is greater than 1.0, then the exposure exceeds safe limits.

     Let’s find out if a worker in a coal fired power plant is at risk of losing his hearing during the course of a typical eight hour workday. Table 2 shows the different noises he has to contend with during that time.

Duration of Exposure (Hrs.) Location Sound Level (dB)
0.5 Steam Turbine Basement 90
2.5 Air Compressor Room 95
0.25 Forced Draft Fan Gallery 110

Table 2 – Example Exposure in an 8 Hour Day

     Now let’s find out if his OSHA recommended sound exposure limit has been exceeded. The values for C, or total time of exposure, are given in the left column, and the corresponding sound level in dB’s is shown in the right column of Table 2. Using these numbers as a reference, we now correlate them with the information contained in Table 1 which cites the OSHA standards. Plugging in the numbers, we find that this worker’s TWAN would be:

TWAN = (0.5 hours ÷ 8 hours) + (2.5 hours ÷ 4 hours) + (0.25 hours ÷ 0.5 hours)

= 1.18

     Since 1.18 is greater than 1.0, we see that the worker’s noise limit would indeed be exceeded. He would need to either wear hearing protection or limit his exposure time in order to comply with OSHA regulations and protect his hearing.

     Next time we’ll discuss options open to us to control sounds in our environment.


Arc Flash Dangers

Sunday, September 13th, 2009

     Imagine being hit by a bolt of lightning.  Like lightning, an arc flash can unexpectedly release tremendous amounts of energy, resulting in serious injuries and even death.

     An arc flash is the result of a short circuit or electrical fault in energized equipment.  Current flows through the air and creates an electrical arc, very much like the phenomenon of lightning.  But unlike lightning, arc flash dangers are present in a myriad of circumstances that do not require storm conditions to manifest.

     Over 80% of electrically related injuries involve some type of arc flash.  They can be caused by a wide variety of factors, including:  equipment malfunctions, inadequate safety procedures, carelessness, lack of training, dropped tools, etc.   The amount of energy released by the electrical arc depends on the amount of electrical current flowing through the arc and how long the current will flow before it is interrupted by a circuit breaker or fuse.

     The radiation released in an arc flash can be so intense and so rapid that it can instantly burn skin and ignite clothing.  Temperatures at the electrical arc can rapidly climb to tens of thousands of degrees.  At temps this extreme metal becomes liquid, then vaporizes, and the air surrounding the arc becomes superheated to approximately 30,000°F.  The superheated air and metal vapor together expand with explosive force.  This creates a dangerous and potentially lethal pressure wave of hot gas, molten metal droplets, and solid metal shards that can create burns and shrapnel wounds. 

arc4 Temperatures at the electrical arc can rapidly climb to tens of thousands of degrees, creating a dangerous and potentially lethal pressure wave of hot gas, molten metal droplets, and solid metal shards that can create burns and shrapnel wounds.

      The Occupational Safety and Health Administration (OSHA) requires employers to assess the workplace for arc flash hazards that are present or that are likely to be present.  Assessment is done using standards developed by the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers (IEEE) to specifically address arc flash hazards.

     If hazards are identified, employers must mitigate risks by adhering to a six point compliance plan such as the following:

1.  Implement a worker safety program with defined responsibilities.

2.  Perform engineering studies that include calculations to determine the degree of arc flash hazards.  These studies also must be updated when any changes to the electrical system are made by the employer or the electric utility. 

3.  Provide workers with the correct personal protective equipment (PPE) based on the study results.  These PPE must then be maintained on site to protect workers.

4.  Provide worker training on the hazards of arc flash. This training must be documented and workers must demonstrate proficiency through testing.  Worker training must also be updated whenever any changes occur to the electrical system.

5.  Provide appropriate tools for safe working.

6.  Place conspicuous warning labels on equipment to warn workers about potential arc flash hazards.

     OSHA, like other government agencies, expects employers to keep up with regulations and take the necessary steps to remain compliant.  For example, OSHA won’t send notices out to employers to inform them that they must implement an arc flash program in their plant.  It’s up to the employers to know that and institute the necessary precautions on their own. 

     It must also be noted that OSHA doesn’t walk employers through the steps of setting up an effective worker safety program.  This means that workers can be exposed to arc flash hazards simply because their employer is ignorant of regulatory requirements and is operating based on misconceptions.

     Some workers are unfortunate enough to work for employers that don’t take potential dangers like arc flash seriously enough to implement an effective safety program.  When their wakeup call comes, it’s often too late.


Do you want to know more about implementing an effective Arc Flash Program in your facility? Phil O’Keefe developed and presents a 90-minute webinar entitled: “Arc Flash Program Fundamentals.”  Contact him for more information about conducting this webinar for your organization.