Why Must Hearing Protective Devices (HPDs) Be Tested?

Transcription

1 PART A Two Part Series on Hearing Protection Devices (HDP s) Why Must Hearing Protective Devices (HPDs) Be Tested? Is It Just for Labelling Purposes? Author: John Franks Ph.D Stay tuned for Part B. The legislative/regulatory background that establishes and complicates the manufacturing, marketing, selection, and wearing of HPDs Research Study by John Franks Ph.D - Why Must Hearing Protective Devices (HPDs) Be Tested? Is It Just for Labelling Purposes?

2 RESEARCH SUMMARY: Why Hearing Protective Devices (HPDs) Are Tested Here s your problem: you have a noisy workplace or workplace activity and you have a person who works in that noisy workplace or conducts the noisy workplace activity. What s your solution? The most obvious is to get rid of the noise, but that can be very difficult for some situations and even after noise controls have been applied, the residual noise may still be hazardous. The next most obvious solution is to get rid of the person. Seems crass, but getting rid of the person can be as simple as putting a barrier between the noise source and the person or putting the person into an enclosure from which to operate. But many workplaces or activities can t accommodate such interventions. So, your problem is how to select the correct Hearing Protective Device (HPD) for that person. That should be simple. Just read the Noise Reduction Rating (NRR) value off the label, subtract 7 to account for the fact you measured your noiseexposure level with the meter set to measure decibels (db) with the A-weighted scale (dba) rather than with the C-weighted scale (dbc), divide the difference by 2, and then subtract the dividend from the noise exposure level to determine the protected exposure level. If it s below 80 dba, it s safe. If it s above 70 dba, it s not over protective. Of course, that s all true if the NRR is used as a benchmark. But, it isn t. It s a number that is supposed to predict the minimum amount of protection that 98% of users will receive. The NRR is a lower boundary, the lowest value that should be expected for 98% of wearers. 2

3 SOLUTION & FINDINGS: In this paper I ll show that testing HPDs has less to do with complying with the EPA s labelling requirements and everything to do with making effective choices for the hearing loss prevention program. To help you understand my conclusions, I ll trace the history of hearing loss prevention as affected by protectors and highlight some of the pitfalls in trying to preserve hearing. I. Background on how HPDs function and the development of HPDs. HPDs are designed to reduce the amount of sound reaching the eardrum by obstructing the ear canal. Regardless of features, shapes, or configurations, the process is the same for all types of HPDs. They either cover the ear as with earmuffs, occlude the entrance to the ear canal as with canal caps, or they fill the ear canal as with earplugs. The HPD has been a work in progress for more than 125 years. As shown in the timeline in Figure 1, the first earmuff was developed in 1873 by 15-year old Chester Greenwood, but not patented until His patent is still cited as prior art in modern patent applications for earmuffs. Chester Greenwood Day is celebrated on his birth date in his hometown of Farmington, ME. The Chester Greenwood & Company factory produced and shipped Champion Ear Protectors worldwide. In 1936 the company had its biggest year producing 400,000 pairs. The company still sells HPDs today under the Champion brand with a claimed noise reduction of 25 db. 3

4 Figure 1: types of HPDs from earmuffs to custom-moulded earplugs. Since 1873, there have been many new types of HPDs developed. Some have flourished, such as the ubiquitous formable slow-recovery foam earplug (Laser Lite Earplugs and 3M E A R Classic ). Some have fallen by the wayside, such as the glass fibre ear down earplug and the single-flange polyvinyl earplug (E A R Noise Filter and Bilsom V51-R). Also shown in Figure 1 are illustrations of types of HPDs from earmuffs to custom-moulded earplugs. Regardless of type of HPD, the common factor to all was the reduction in sound levels reaching the eardrum. It wasn t until the late 1950s that methods were developed for measuring the extent of the sound reduction. II. What makes selecting the correct HPDs so difficult? 4

5 The HPD is a complex acoustic system in spite of its appearance to be otherwise. How can a simple piece of foam, plastic, silicon, or an earcup be complex? Even the answer to that question is not simple, but the key points are as follows The head and ear are not simple systems. The eye, by comparison, is a walk in the park. Acoustics is the oldest branch of the oldest science, physics. Optics is the next oldest branch. Galileo was building telescopes almost 100 years before William Derham was beginning to calculate the speed of sound using a telescope and stopwatch. The biblical Joshua may have taken down the walls of Jericho with the sound of trumpets, but it s been a lost art since. Only in this century have truly effective sound cannons been developed, and then to control personnel, not to take out structures. At this point, acoustics, and its physiologic partner audition, are still the least well understood of most of the classical physics entities. Most mechanical/acoustic engineering constructs fail to accurately describe the ear, earmuffs, and earplugs. Most of the rules for acoustics and for mechanical systems that affect acoustics were written and studied for large-scale systems. In large systems, differences on the order of 3 decibels (db) are considered negligible. On the other hand, when an earplug has a change in effectiveness of 3 db, it is often put into a different class. A change of 3 db in noise exposure level can markedly reduce or increase the risk of noise-induced hearing loss (NIHL). The National Institute for Occupational Safety and Health (NIOSH) estimates the prevalence of NIHL for those exposed to 80 dba or less to be 1%, while at 82 dba it increases to 5%, at 85 it increases to 12%, to 20% at 88 dba, and at 90 dba the prevalence increases to 25%. 5 The simplest earplug should be a piece of dense slow-recovery foam compressed and inserted deeply into the ear canal. It acts as a mass enclosing

6 the residual air in the ear canal that couples to the eardrum and the air trapped in the middle ear. A simple mass-loaded system such as this same earplug inserted into a hole drilled into a solid block will increase attenuation at 6 db per octave over the measureable frequency range. This increase in attenuation will apply for the ear until the acoustics of the ear canal, the middle ear, and head come into play above 500 Hz. Above 500 Hz, the attenuation for the earplug will begin to level off. Figure 2 displays the difference between a simple plug in a tube and a similar plug in the ear canal. Figure 2. Attenuation of an earplug in a tube and the earplug in the ear. For the purposes of the example, the two trends have been matched at 125 Hz. The Frequency axis is logarithmic rather than linear. 6 Next, insert a hole into the earplug, itself with a smaller hole. This creates a complex filtering system that will do one thing with certainty: reduce the attenuation of the plug. How much and for which frequencies depends on many factors, the largest of which is the interaction of the head and ear with this complex acoustic system. To date there doesn t exist a mathematical acoustical model of such a system that is anywhere near predictable within 3 db. Design

7 of such systems is often by trial and error. The research is often trying to catch up to the physical designs rather than the research leading the designs. Figure 3 shows an example of the differences between a solid earplug and the same earplug with a hole fitted with filters. Figure 3. Attenuation of a solid earplug and the same earplug with a hole fitted with filters. These data were obtained according to ANSI S3.19 on a panel of 10 subjects. The Frequency axis is logarithmic rather than linear. HPDs are complex enough that change of one element changes the entire device. Any change in an HPD design, including the insertion of a vent or filter, must be treated as a new system. There is no such thing as a series of HPD components that may be combined to create a new, known, system. Since it is not possible to accurately create an acoustic model of a simple earplug, or especially one with a vent, it is not possible to specify performance for any HPD without testing that particular configuration. While an insert may be expected to alter attenuation by 10 db based on measurements of the insert alone, it may or may not once put into an HPD. The only way to ascertain that is to test the new HPD. 7

8 HISTORY: 8 III. A short history of development of testing procedures and ratings schemes and their impact on government regulations s Until the 1950s, there was no standardized method for determining the amount of noise reduction that HPDs provided. There were also no labelling requirements for describing effectiveness. Among issues were whether to test HPDs using physical measurements or psychoacoustic procedures. The goal was to develop a testing method that provided data that were predictive of how the HPD would work with a person who must wear it in noise. Of course, the data had to be repeatable across measurement sessions and between laboratories. At first it seemed that If a physical measurement were used, it would be on a test fixture that mimicked average human head and ear. With such a test fixture a microphone could be placed at the end of the simulated ear canal. While providing a measurement of insertion loss, how the data could be related to a human user was a concern. Would the data be adequately predictive of how a person might experience the effect of the earmuff or earplug? 1970 s However, over 65 years later there has not been a commercial acoustic manikin that can fully simulate the human head and ear canal for the purpose of

9 measuring the insertion loss due to the hearing protector. The early manikins culminating with the Knowles Electronics Manikin for Acoustic Research (KEMAR) from 1973, were designed for measuring open sound fields or the gain from hearing aids, not HPDs. Also, there has been no commercial artificial skin that could line a surrogate ear canal for fitting earplugs 1. Ideally, specifying HPD performance characteristics could be a process similar to how hearing aid performance is specified. Figure 4 shows KEMAR, the external features of which have remained unchanged over the years. 1 The just introduced successor to KEMAR has extensive insertion loss, appropriateness for measuring impulsive noises, and artificial skin for lining the side of the head and ear canal. There have not been extensive studies with it to determine if it may someday be used for definitive measures of HPD performance. 9

10 Figure 4. The Knowles Electronics Mannequin for Acoustic Research (KEMAR) displayed wearing safety glasses. Note that the shading of the pinna is different than the head; there are three pinna sizes. For now, this makes using human test subjects necessary. Physical measurements can be taken with two sub-miniature microphones, one placed just inside the ear and one placed outside the open and occluded ear canal to measure noise reduction or attenuation. Or, one microphone could be placed inside the open and occluded ear canal, with no movement of the microphone for either condition to measure insertion loss. The use of microphones is referred to as a microphone-in-real-ear (MIRE) method and is addressed in ANSI S Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise Using Microphone-in- Real-Ear or Acoustic Test Fixture Procedures). A variation of the twomicrophone MIRE method for fit-testing in the field is the 3M EARfit system. It uses two microphones, one of which is inserted into a surrogate earplug to ascertain the attenuation achieved with the earplug by the wearer. Psychoacoustic methods require asking a listener to participate in some sort of task such as reporting changes in loudness or taking hearing threshold tests with and without wearing the HPD. Loudness balance compares the difference in perceived loudness the HPD causes in one ear fitted with the HPD compared to the other ear being open. Measuring a change in hearing sensitivity (threshold shift) wearing the HPD causes has been labelled real-ear attenuation at threshold (REAT) Regardless of method, loudness balance or REAT, the outcome is insertion loss. There have been a series of standards developed for testing HPDs. As each new standard has been introduced and used, shortcomings and errors have required the development of a new standard because the changes necessary were beyond the scope of a simple revision. 10

11 The first American standardized procedure testing HPDs used REAT. Repeated REAT measures were taken for a group of normal-hearing subjects for pure tones (ANSI-Z Method for the Measurement of the Real-Ear Attenuation of Ear Protectors at Threshold). The standard was eventually rescinded because of its reliance on testing with pure tones in an anechoic (no echo) chamber. The next generation American standardized procedure required the testing of hearing protectors in a diffuse sound field achieved by testing in a reverberation chamber with specified maximum and minimum durations of echo (ANSI S , Standard Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs). Instead of pure tones, onethird-octave bands of noise were centered at the octave frequencies from 125 to 8000 Hz with the insertion of 3000 and 6000 Hz. The standard called for two methods of fitting the HPDs: 1) subject-fit, which effectively locked the experimenter out of the fitting process even if the subject misfit the HPD, and 2) experimenter-fit, which effectively turned the test subject into a surrogate manikin for the fitting process. When the U.S. Congress passed the Noise Control Act of 1972, it charged the U.S. Environmental Protection Agency (EPA) with identifying and labelling the noise emission or noise reduction provided by any commercially available products as would be experienced by the consuming public. In 1979, when the EPA released its rule for the labelling of HPDs sold in the United States, whether for occupational or non-occupational use (40 CFR , Subpart B), it required use of the experimenter-fit method of ANSI S3.19. The general thought at the time the regulation was developed was that if the experimenter-fit method were to be used, the data would reflect the bestexpected outcome for trained and motivated users. The subject-fit method was dismissed. 11

12 This seems contrary to the intent of the Noise Control Act, since ANSI S3.19 states that the subject-fit method would reflect an average outcome, whereas the experimenter-fit method would reflect an excellent outcome. The average consumer and noise-exposed worker lacks access to second party to either physically fit or at least inspect the fit of the HPD The NRR was developed by the EPA to predict the theoretical A-weighted protected noise-exposure level for the HPD user given a known C-weighted unprotected noise-exposure level. Alternatively, if only the A-weighted unprotected noise-exposure level were known, the NRR could be reduced by 7 db. Further, the NRR was statistically designed to be a value that 98 percent of those who fitted the HPD as was done by the experimenter or correctly - would exceed. Thus, the NRR was never intended to be a benchmark. It was intended to be the lower boundary Meantime, as early as 1974, data obtained from workers using HPDs tested with a large earcup and the same noise bands and procedures as required by ANSI S3.19 showed great discrepancies between their now-called real-world REATs and the laboratory REATs on the labels. By 1994, results from 22 such studies showed that the laboratory REATs exceeded the real-world REATs by as little as 5% for earmuffs and as much as 2000% for some earplugs. Thus, the labelled NRR - the baseline value that 98% of HPD users were supposed to exceed so grossly overstated HPD performance that it could be considered as bogus, or useless. (More on what to do with this useless number is below.) Mid 1990 s 12 In the mid-1990s, the working group responsible for ANSI S3.19 began developing a new ANSI standard. A series of inter-laboratory studies were

13 conducted evaluating both the experimenter-fit and subject-fit methods with the goal of improving both methods. Of importance were the variability of the data between test subjects and the variability of the data between laboratories. From the first of the studies, it also became obvious that the subject-fit method provided data that were very close to the real-world data for most of the HPDs tested. Further, the inter-laboratory variability was less for the subject-fit method than the experimenter-fit method. Stated otherwise, the subject-fit baseline data were more repeatable from test to test and were more reproducible from laboratory to laboratory than the experimenter-fit data. The current version of the new ANSI standard for testing HPDs is ANSI S , Methods for Measuring the Real-Ear Attenuation of Hearing Protectors. The experimenter-fit method has been highly revised to reduce the effect of the experimenter in the actual fitting of the HPD being tested and is now referred to as Method A. Method B of the standard is the subject-fit method, which also has been revised over the generations of S12.6 to reduce variability 2. Common to both methods is the increase in the number of test subjects from 10 to 20 for all HPDs except earmuffs. Second is that the number of test repetitions per subject is reduced from three to two. Third is that the determination of the mean REATs and standard deviations are calculated correctly, whereas in S3.19 they were not. The calculation of the NRR had been created for and included in the EPA labelling rule, but never in an ANSI standard. In order to manage data from ANSI S12.6, a new standard was developed for using the data for both 2 Regrettably, we are still using the S methodology for testing hearing protection for the purpose of labeling because the EPA has not changed 40 CFR Part 211 Subpart B that is based on that withdrawn standard. 13

14 Methods A and B (ANSI S (R2012) Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors Are Worn). ANSI S12.68 was included in the proposed revision to the EPA s HPD labeling rule, but that revision has never been promulgated, and so the standard has become moot. NRR VS. SNR: IV. NRR and SNR: what these mean and how they are (miss)used. Using the NRR in a HPD Attenuation Calculation 8-hour TWA noise exposure: 93 dba NRR of hearing protectors: 29 db Subtract 7 db from the NRR: 29 db - 7 db = 22 db Divide by 2: 22 2 = 11 db Subtract 11 db from the 8-hour TWA noise exposure: 93 dba - 11 db = 82 db Decide if 82 db (known as the Protected Exposure ) is below the 85 dba PEL for noise The NRR: 14 The NRR: However, when applied by Industrial Hygienists and hearing loss prevention professionals these have been used as a benchmarks or target values. The NRR, as stated above, was intended to provide the HPD selector with a number that could be subtracted from the noise-exposure level in dbc to provide the protected noise-exposure level dba as applied to the NRR by the

15 U.S. Occupational Safety and Health Administration (OSHA) in 29 CFR App B. Since the NRR had been found to overestimate the amount of protection afforded by the HPD, OSHA, for calculations to determine if the HPD could afford adequate protection divided the dbc dba corrected value by two (Appendix E--Noise Reduction Rating). So, in the example below, the NRR of 29 db is supposed to be achievable by 98% of users. That value is first corrected to 22 db in order to be used with A- weighted noise exposure levels. The 22 db is then divided by 2 and reduced to 11 db. The 11 db is subtracted from the noise exposure level (93 dba) in this example, to provide the Protected Exposure Level of 82 dba, which, being less than OSHA s target Permissible Exposure Level of 85 dba is adequate. Said another way, more than 98% of users with exposure levels of 93 dba or less could be expected to be protected by this HPD according to OSHA s criteria. By 1998, after conducting further comparisons between real-world and laboratory NRRs as well as an intensive analysis of samples of workplace noise spectra, NIOSH suggested that the correction for A-weighted noise exposure level be 3 db instead of 7 db. Further NIOSH recommended that HPD-type derating factors be set as follows: 0 percent for laboratory-made custommoulded earplugs, 25 percent for earmuffs, 50 percent for slow-recovery foam earplugs, and 70 percent for pre-moulded earplugs. NIOSH also suggested that the targeted range for protected exposure levels should be less than 80 dba and greater than 70 dba. 15 As the first generation of ANSI S12.6 had been published a year earlier, NIOSH, which had been involved in much of the research that supported the standard, recommended in 1998 that HPDs should be tested according to the subject-fit method and labelled according with the NRR(SF), using the same calculation method as for the NRR. The NRR(SF) could be used with the 3 db

16 C- to A-weighting correction factor and could be used without derating according to protector type. However, even NIOSH considered the NRR ((SF) as a benchmark rather than the lower boundary. The NIOSH HPD Compendium presently lists the NRRs for 197 HPDs as well as the NRR(SF) based on ANSI S12.6 Method B procedures for many of the earplugs and custom-moulded earplugs. The SNR The SNR (Single-Number Rating) has long been used in Europe and elsewhere and is defined in ISO/TS (Part 2: Estimation of effective A-weighted sound pressure levels when hearing protectors are worn.). The standard assumes that the noise exposure measures can be converted to whatever weighting is necessary and so designed the SNR as to be weighting free. It is typically applied at the 80 th percentile, which is equivalent to the mean value minus 1.84 standard deviations and is noted as the SNR 80. Where minus 2 standard deviations applied, it would be at the 98 th percentile and notated as the SNR 98. CLICK HERE ISO :1990 While ISO :1990 (Acoustics -- Hearing protectors -- Part 1: Subjective method for the measurement of sound attenuation) called for the use of test subjects familiar with the use of HPDs, it did not require that the experimenter fit the HPD under test. It also called for the use of 16 subjects rather than the 10 of ANSI S3.19, and for two repetitions each instead of three. Essentially, experienced test subjects could visit the laboratory, select from among the HPDs to be tested that day, and sit through no more than two sets of tests per HPD for no more than two HPDs per day. Some laboratories were extremely controlling as to how subjects were tested and some were lax. Not surprisingly, 16

17 the data were similar regardless of level of laboratory control. So long as the experimenter did not actually fit the HPD being tested, as they did in the U.S. for compliance with EPA rules, tests results were driven by the HPD alone and not the experimenter s interpretation of how the HPD should be best fit. Those countries adopting ISO 4869 as the primary standard have also adopted or developed with own versions of ISO 4869 Acoustics Part 5: (Hearing protectors. Method for estimation of noise reduction using fitting by inexperienced test subjects) There was international cooperation between the working groups and task forces developing this standard along with Method B of ANSI S12.6. Thus the procedures are quite similar. Testing conducted according to this standard may be used to calculate the SNR(SF84),00000 that is the lower boundary limit at the 84 th percentile for the HPD s assumed protection. However, for labeling purposes, the SNR( 80 ) is used with procedures from ISO What has not been done, or at least reported, are studies comparing the SNR( 80 ) and SNR(SF84) since the involvement of the experimenter in both procedures is minimal and the critical difference is the familiarity of the test subjects with HPD use. 17

18 V. What does this mean? What is the concerned industrial hygienist, audiologist, or consumer to do? Here are 5 rules to guide you. Rule 1. Be informed. The primary problem with HPDs is that they vary widely in effectiveness from individual to individual. That is why in this paper, the emphasis has been put on recognizing that whatever rating is used, it is a lower boundary, not a benchmark. The rating is a statistic derived from laboratory studies on small groups of people. That statistic is extrapolated to large populations. So, for single-number ratings such as the NRR or the SNR, the value, be it the 80 th, 84 th, or 98 th percentile is the value, such as the derated NRR or SNR, HPD users are supposed to achieve more attenuation that that number. Rule 2. Recognize that HPDs, the head, and the ear are complex systems. As discussed above, the acoustics of HPDs aren t accurately described by the principles of acoustics that were derived for large-scale systems such as walls, doors, windows, churches, and concert halls. HPDs and the head and ear to which they couple are a system. Change one element, or one part of one element of that system, and the entire system changes. Even with the problems associated with HPD testing and rating methods, each variation of an HPD must be tested. There is no room for extrapolation. 18 The methods in use today for labeling HPDs address only the passive attenuation. If an HPD is fitted with a filter that is supposed to increase attenuation with increasing sound levels, there is no regulatory method for labeling it. The communication headsets that are used for everything from aviation to construction have no standardized method for determining the Research Study by Dr. John Franks Why Must Hearing Protective Devices (HPDs) Be Tested? Is It Just for Labelling Purposes?

19 combined exposure level of attenuation noise and sound delivered by the communication system. There is no regulatory method for rating an earmuff or earplug fitted with automatic noise reduction or noise cancelling circuitry. Similarly, for sound restoration systems that are supposed to allow low-level sounds through with attenuation increasing until the HPD is in full passive mode, there are no regulatory methods for rating. As well, claims made as to the benefits of various features are too often made in the absence of any data and are based at best on inference or anecdotes. Logically, it should be easier to understand speech in noise if the HPD has been designed to have a flat attenuation characteristic, but the supporting data are lacking. Similarly, the electronic HPDs, be they earmuffs or earplugs, should allow good situational awareness in low noise levels, but the few studies indicate otherwise 3. Rule 3. Employ fit testing if possible. The so-called gold standard for determining the effectiveness of an HPD is REAT. REAT methods can be applied at the worksite as well. The any type of fit-testing procedure is referred to as FAES - Field Attenuation Estimation System. There is not yet a standardized procedure for evaluating FAES, and there are six commercially available systems. However, only one FAES provides a REAT-type result. It has been around in various forms since the early 1970s, but the commercial version now available is the HPD Well-Fit developed by NIOSH and licensed as FitCheck Solo. 3 Casali, J. G. and Robinette, M. B. Effects of user training with electronically modulated sound transmission hearing protectors and the open ear on horizontal localization ability. International Journal of Audiology, December 2014,

20 The result of fit testing is the Personal Attenuation Rating (PAR). Unlike the NRR, the PAR may be applied directly to the person s noise-exposure level. Either FitCheck Solo, or 3M EARfit procedure with its personal MIRE technique, provide a PAR. As well, both systems provide computer software that performs the necessary calculations to account for noise-exposure levels measured in dba and the known repeatability of the test results for the tested HPD. For each particular user, the PAR may be directly subtracted from the noise-exposure level (in dba) to see if the protected noise-exposure level is low enough; that is between 70 and 80 dba. If the protected exposure level is still too high, then a different HPD may be considered or better training with the present HPD may be effective. If the protected level is too low, lower than 70 dba, then a different HPD may be considered as well. FAES may be employed as part of the periodic audiometry program, requiring only a small increase in time for the testing protocol. FAES may also be employed any time an exposed person is issued and trained in the use of HPDs, whenever a noise-exposed person experiences a threshold shift, or whenever there is concern that the HPD currently used may be under or over protecting. Field Attenuation Estimation System. The purpose of FAES is not to have the HPD user achieve the labeled value for the HPD, such as the NRR. The purpose of FAES is to insure that whatever HPD is used is effective for the individual s noise exposure level. 20

21 Rule 4. Select the HPD with the lowest possible NRR or, if available, the best SNR(SF84) for the noise exposure levels of concern. The trend, globally it seems, for the past 50 years has been to select the HPD with the highest NRR. If an NRR of 25 db is good, 30 db is better, and 35 db is best. And, the manufacturers of HPDs have followed suit. This has resulted in many HPDs on the market that are totally overprotective if they actually deliver as promised. When a manufacture was asked, Why not make an HPD with an NRR of 15 if that s all that s needed? The answer was to the effect that HPDs with NRRs of 29 would outsell it even though many workers need 15 db or less attenuation. This is even more important of an issue when the NRR is considered as the lower boundary, not the benchmark. Rule 5. Check the testing laboratory. There are only a few independent facilities for testing HPDs, and a couple that belong to manufacturers. In general, try to ascertain if the testing laboratory is independent from the manufacturer. The present EPA labeling rule requires the testing method and laboratory to be listed. Also, confirm that the laboratory regularly tests HPDs. There is no requirement that HPDs regularly be retested, so for some products the data may be more than 30 years old from a laboratory that tested only one product. In general, the older the data, the less reliable they are. Also beware of excessively small standard deviations on the label. Typically, the standard deviations should be no smaller than 3 db. Stay tuned for Part B. The legislative/regulatory background that establishes and complicates the manufacturing, marketing, selection, and wearing of HPDs 21