Applying customisation technology to hearing protection

Why with a world full of available hearing protection do we still have millions of people losing their hearing? Noise in the workplace has been designated by the World Health Organisation (WHO) as the world's single largest occupational health problem. This is not a problem that effects only countries with poor OH&S practices either. The industrialised world with all its policies, procedures, rules and regulations has not been able to stop the growth of noise induced hearing loss (NIHL) within its labour forces.

The 1995 National Health Survey lists 9.4% of Australians as having self-reported hearing loss. That equates to 1.7 million people. The 2001 survey put that figure at 13.5%. That's a staggering 900,000 new cases in six years. Obviously not all are industrial related but even assuming 50% that still leaves over 6000 new cases a month. It's no wonder that the Australian National Occupational Health and Safety Commission (NOHSC) refers to hearing loss as a 'disease'.

The average compensation payment for NIHL in Australia according to the Noise 2003 report from NOHSC was $6000. The South Australian Workcover Authority estimates that the average cost to Australian business per claim is $30,000, taking into account lost hours, insurance costs etc. The NOHSC report also points out that as much as $247 million taxpayer dollars were spent by the Department of Health and ageing in providing hearing rehabilitation services in the 2002 tax year.

NIHL is preventable. OH&S legislation and policy have mandated the use of hearing protection devices (HPDs) for over 20 years. Still we have a problem. Studies over recent years have indicated two main reasons for NIHL to still be so prevalent in the modern world. Firstly, the protection rating of an HPD often doesn't truly match the attenuation achieved in the real world. Secondly, people don't wear their hearing protection correctly or regularly enough. Both reasons have underlying causes and both, given recent technology enhancements, can now be rectified.

In Chapter 29 of Scientific Basis of NIHL, published by Thieme Medical Publications of New York, three auditory research scientists - Berger, Franks, and Lindgren - reviewed the findings from various international field studies of HPD attenuation. The studies take into account 90 different industries in seven countries and involve almost 3000 workers. They concluded that the 'real world' attenuation results of hearing protectors is far less and varies greatly from the results measured in a laboratory. Laboratory measurements are, in fact, the way an ear plug or ear muff is rated for its labelled class of protection level. Without individual testing people must wait until their next annual hearing test to determine if their protection worked or if they suffered irreversible hearing loss.

The fact people don't wear hearing protection correctly is either intentional or a feature of lack of instruction. Berger, Franks and Lindgren also concluded that a large variation exists in the way a specific HPD is worn. This results in a wide inconsistency of attenuation results. It may not seem like rocket science to fit a foam plug in your ear but a report in Noise & Health Vol 7;25 by Warwick Williams, senior research engineer with the National Acoustics Laboratory in Sydney, shows the importance of fitting instructions. Forty people were tested under Australian Standards protocol with a single type of foam ear plug. Twenty of the subjects were shown instructions on the fitting technique and 20 were not. The 20 subjects receiving instruction achieved an SLC80 of 24 versus an SLC80 of only eight from the 20 subjects with no instruction. That is a serious difference. How many workers wearing HPDs have had individual instruction or bother to read the packet?

Even if instructed properly some people find all manner of ways to avoid wearing an HPD correctly. There are many reasons for this intentional misuse. The most common criticism about an HPD is lack of comfort. Both plugs and muffs suffer the same backlash. Earmuffs are hot, too tight and interfere with other protective gear. They are also often worn with protective eyewear which can render them ineffective as they no longer seal around the ear correctly.

With little significant improvement since their introduction 35 years ago, 'one-size-fits-all' foam plugs still account for more than three-quarters of the hearing protection market. These HPDs cannot be designed to fit the millions of different ears which are individually unique in shape and size. Each insertion of foam plugs achieves an unpredictable and unmeasurable result. When inserted properly they tend to cause discomfort due to outward pressure and friction points, so that all too often, people simply insert them at the outer edge of their ears, pretending to comply. People who take protection seriously insert them well into the ear, often achieving the necessary acoustic seal, but at the cost of their ability to hear danger signals and to communicate in a noisy environment. This necessitates their removal in order to communicate. This is less than ideal because hearing damage from noise is cumulative and requires HPDs to work perfectly and to be worn all of the time. Anything short of optimal performance and continuous use can dramatically compromise overall protection and allow damage to occur.

The Australian/New Zealand Standard for Occupation Noise Management (AS/NZS:1269) dedicates Section 3 to the Hearing Protection Program. This standard advises on the importance of selecting the correct hearing protection for your site. It should not come down to a decision on simply choosing the HPD with the best rating. Over-protection also is a serious issue. Not only do people feel isolated, it has the effect of increasing the risk of injury.

Technology, however, has finally come to the rescue and the days of noise induced hearing loss as a disease are numbered. A new generation of more effective and yet practical hearing protection products is now available. Instant custom fit HPDs that can be easily measured in every ear without inconvenience and without high costs provide comfort and a quantifiable protection level. In some cases they can be calibrated to match the exposure level of the employee.

The new approach to the fabrication of personalised HPDs from companies like Sonomax permit the development and delivery of personalised HPDs without the need for an initial mould. The HPD is 'cast' in the ear and is completed and delivered on site in a single step. Custom moulded HPDs are comfortable and cannot be worn incorrectly. Because the user is right there at the time of fit they will always receive one-on-one instruction.

Some manufacturers have introduced HPDs designed to provide a high fidelity sound with reduced or limit attenuation, making the HPD more 'natural sounding' and addressing the overprotection issue. The Bilsom NST from Bacou-Daloz and Ear UltraTech or HiFi from Aearo are designed to provide sufficient attenuation for the vast majority of workplace noise environments, while allowing enough high-frequency through to make the perceived sound more natural. Once the personal protection level has been measured it can be combined with the measured exposure level of the employee to calculate the optimum level of protection required. Appropriate selection of acoustic dampers is then used to adjust the devices to the workers' noise exposure and hearing ability.

Employers with formal Hearing Conservation Programs recognise the benefits of these new advances and are embracing them. Rio Tinto's Comalco Smelter at Boyne Island in Queensland was one of the early adopters. During 2005, it has been rolling out custom moulded, custom calibrated hearing protection from Sonomax. Boyne Smelters Limited health and environment manager Vanessa Wharton, said: "The smelters focus is still firmly on reducing noise at the source through engineering solutions, however the new protectors from Sonomax would offer maximum personal protection. The Sonomax protectors have several advantages for us. They are comfortable - they allow easier communication and provide superior protection." BSL was the first site within the Rio Tinto group to implement Sonomax. Three other Comalco sites around Australia have joined them and plans are to provide the unique solution to all employees exposed to significant noise.

Duty of care legislation requires everything "reasonably practicable" to be done to protect the health and safety of people at the workplace. Until recently the only reasonably practical way to address personal hearing protection was with disposable foam plugs, ear muffs or ear canal caps. The alternative to these devices is a custom fitted hearing protector. Unfortunately, until now, the process was cumbersome and expensive therefore was not a practical way for industry to address workplace safety.

Custom moulded HPDs are now possible on a mass scale. It is difficult for a person to fit a moulded HPD in their ear incorrectly thus solving the 'variable fit' issue. Couple this with the ability to test the actual protection level and you can eliminate the risk of the HPD not providing enough or possibly providing too much protection for a given noise exposure. By applying precise measurement to every hearing protector, employers now have the capability to complete a Hearing Conservation Program with a quantifiable result.

Scientific measurement has been used for decades to measure environmental noise and individual hearing ability. Now, those same principles can be applied to the measurement of the last line of defence against noise, the humble HPD.