ALN about NRR A Little Noise about Noise Reduction Ratings

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ALN about NRR - A Little Noise about Noise
Reduction Ratings

• Presented at the
• 2007 Tidewater LS AIHA Fall PDC on Nov 16, 2007
  by Christopher D. Jones, MS, CIH
• NAVMEDCEN Portsmouth, IH Department

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BACKGROUND

• Think back, way back, to your early career
  education in industrial hygiene or safety, to the
  time you first heard about "the hierarchy of
  controls"

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BACKGROUND

• Remember them?
• Engineering controls then
• Administrative controls and finally
• Personal Protective Equipment
• We are all pretty comfortable with this method of
  prioritization to respond to occupational
  stressors in our workplace when we are assessing
  personnel exposures to odds and ends

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BACKGROUND

• For some reason, it is second nature for us to
  recommend an engineering control for paint mist
  before we jump on a respirator .

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BACKGROUND

• But we forget all about this when we are dealing
  with noise put plugs in their ears or muffs on
  their head is often choice 1, not choice 3

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BACKGROUND

• If we put someone in a half mask respirator for
  protection against dust, what is the assigned
  protection factor for that mask/filter
  combination?
• Ten - regardless of respirator manufacturer
• If, on the other hand, you put earplugs inside
  the ear canal of an employee, what is the
  "assigned protection factor" for that plug?
• It depends on who made the plug

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WHAT'S AN NRR?

• The EPA requires that HPDs be labeled with their
  noise reduction rating, the NRR a single number
  rating of the hearing protection the higher the
  NRR, the higher the attenuation for a specific
  ideal situation ("The Occupational Environment -
  Its Evaluation and Control", aka., the "White
  Book", AIHA, 1997)
• Two kinds, A the one on the box and B a
  subject/fit NRR, a special one, hard to find
• Test frequencies 125, 250, 500, 1000, 2000,
  3150, 4000, 6300 and 8000 Hz

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WHAT'S AN NRR?

• The NRR doesn't provide an accurate estimate of
  the true attenuation provided to the wearer,
  because it can be affected by fit, insertion
  technique, and the noise level in the work
  environment
• Since the NRR isn't a solid number to hang your
  hat on, how do you use it?
• "Derate" it - adjust it in some fashion to better
  reflect a "real world" level of protection that
  the HPD provides

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DERATING AN NRR - the OSHA way

• Adjust or derate the NRR, then compare the new
  to your measured noise exposure
• In Appendix B of OSHA's general industry noise
  standard, 29 CFR 1910.95, OSHA recommends a
  method to derate the NRR to determine the
  adequacy of selected HPD
• Estimated Exposure (dBA) TWA (dBA) - (NRR -7)
• If using dBC values, Estimated dBA TWA (dBC) -
  NRR
• Example TWA 100 dBA NRR 19
• X 100 - (19 - 7) 88 dBA

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DERATING AN NRR - the OSHA way

• How do you derate double hearing protection?
• OSHA says 5 dB can be added to the NRR of the
  most protective device
• Example Noise TWA 100 dBA NRR 19 for a
  muff, 30 for a plug the assigned NRR for this
  combo is 30 5 35
• Estimated Exposure (dBA) TWA (dBA) - (NRR -7)
• X 100 - (35 - 7) 72 dBA

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DERATING AN NRR - the OSHA way, Part II

• OSHA directs inspectors to take into
  consideration the relative performance of HPDs
  derate the NRR by 50 (E.A.R Log 20, "The Naked
  Truth About NRRs", Cabot Safety, 1993 also found
  on OSHA's web site at www.osha.gov/dts/osta/otm/no
  ise/hcp/
• attenuation_estimation.html)
• This derating has no relationship to the just
  mentioned 7 dB correction spelled out in 1910.95
  this derating adjusts NRRs to "real world"
  performance, whereas the 7 dB correction adjusts
  the NRR to a dBA measurement

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DERATING AN NRR - the OSHA way, Part II

• So here's how OSHA inspectors derate HPDs to
  determine the relative performance of HPDs
• they cut it in half!
• Estimated Exposure (dBA) TWA (dBA) - (NRR -7)
  X 50
• Example TWA 100 dBA NRR 19
• Estim. Exposure 100 - (19 - 7) X 50 94 dBA
  
• The relative performance of an NRR of 19 is 6

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DERATING AN NRR - the NIOSH way

• NIOSH has an even more exciting way to determine
  a "true" NRR the NRR is adjusted by the type of
  protection you are getting ready to wear (see
  "Criteria for a Recommended Standard,
  Occupational Noise Exposure, Revised Criteria
  1998 " NIOSH, 1998)
• Earmuffs subtract 25 from the MFR NRR
• Formable plugs subtract 50 from the MFR NRR
• All other plugs subtract 70 from the MFR NRR

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DERATING AN NRR - the NIOSH way

• So here's how NIOSH asks you to derate HPDs
• Effective A-weighted noise level (ENL, dBA)
• dBA - (derated NRR -7)
• Example ENL TWA 100 dBA NRR 19
• Muffs 100 - (19 X .75 14) - 7 93 dBA
• Form. plugs 100 - (19 X .50 10) - 7 97
  dBA
• Other plugs 100 - (19 X .30 6) - 7 101
  dBA ?
• Whoa, it got louder???

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REAL WORLD CYPHERIN' WITH DERATED NRRs

• We (NAVMEDCEN Portsmouth IH Dept) have started
  collecting noise dosimetry data and paying more
  attention to the brand of HPD in use by the
  sampled individual
• We can take our measured TWA (dBA), compare it to
  the derated NRR, and calculate a "corrected TWA"
• This will help us make determinations about HPD
  effectiveness might cause us to pursue new
  brands of HPDs instead of the brands currently in
  use

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REAL WORLD CYPHERIN' WITH DERATED NRRs

• There are multiple OELs in our IH world
• OSHA 90 dBA, 5 dB exchange rate
• ACGIH 85 dBA, 3 dB exchange rate
• DOD 85 dBA, 3 dB exchange rate
• US Navy 84 dBA, 4 dB exchange rate
• We measured five TWAs at one facility (an
  aircraft squadron) and three were Navy OEL or
  84 dBA after derating, two of the exposures were
  still above the Navy OEL
• Let's look .

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REAL WORLD CYPHERIN' WITH DERATED NRRs

• Adjusted TWAs after derating MFR NRRs

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DERATING AN NRR - the super cool 21st Century way

• You can have an NRR that is specific to you and a
  particular insert plug - personalized just for
  you
• Takes into consideration the way you inserted the
  plug, the shape of your ear canal, and your
  hearing thresholds at the testing frequencies
• A new hardware/software combo, "Fit Check" from
  Michael and Associates (michaelassociates.com)
  allows you to insert plugs (or wear muffs), put
  on some headphones, and get an audiometric test
  while wearing those plugs results given as a
  personal attenuation rating (PAR)

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DERATING AN NRR - the super cool 21st Century way

• Three plugs, one head (mine), four ways of
  looking at them PAR personal attenuation
  rating

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WHAT DOES THIS ALL MEAN?

• We probably ought to take a closer look at the
  brands and types of HPDs that are being worn in
  our facilities an NRR in single digits is not
  doing anyone any favors
• If you routinely use insert plugs, grab moldable
  plugs they usually have an NRR of around 30
• If you use the OSHA 1910.95 Appendix B protocol,
• (NRR -7), then a 30 is a 23
• If you use the OSHA 50 derating protocol,
• (NRR -7) X 50, then a 30 is a 12

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WHAT DOES THIS ALL MEAN?

• If turtles could fly and we all had budgets that
  are appropriate for what we do we'd determine
  PARS for each of our employees so we could give
  them the best plug possible
• Just three grand puts the Fit Check system in
  your hand!
• Perfect plugs prevent poor performance!

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CONCLUSION

• Any questions? Now go forth and measure, brothers
  and sisters