Starck J, Toppila E, Laitinen H
Director of the Department of Physics, Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, 00250 Helsinki, Finland.
Noise Health. 2005 Jan-Mar;7(26):47-53. doi: 10.4103/1463-1741.31640.
The type test of hearing protectors (HPD) for certification purposes will be conducted in laboratory at room temperature. Optionally, the mechanical durability of HPDs will be tested in cold environment by a drop test. The purpose of this study was to find out the relevance of the drop test, the change of performance in HPD protection, and finally to estimate the possible change of protection efficiency against noise in cold environment. In total, 22 HPDs were selected to the measurements: 18 earmuffs, and 4 earmuffs attached to an industrial helmet. Attenuation of each earmuff cup was measured by applying insertion loss method for the test subjects in cold. The change of attenuation and temperature of cushion ring was followed up to nine minutes using 30-second intervals for sampling. Three HPDs were damaged in the test. The replaceable cushion was broken in two earmuffs and in one helmet-mounted HPD. The replaceable parts were replaced, and the HPD with attachment failure was removed from insertion loss measurement. In nine HPDs the relative change was less than 3 dB, and was at worst 10 dB. This change was typically at low frequencies, 125 Hz at the beginning when cooled HPDs were placed. In various HPDs the time to get the attenuation levelled varied from 1.5 minutes to 8 minutes. The recovery was dependent on the temperature of the cushion ring. In all cases the temperature of the full attenuation was achieved when the cushion ring reached 7 degrees C. This temporary decrease in attenuation will have a minor effect to the protection efficiency, when the HPD is used full time during the whole exposure duration. A typical group of forest workers will have their exposure interrupted. The chain saws have to refuel, and the chain needs to be sharpened about every 40 minutes. During 6 hour daily operational time there will be about 9-10 minute break, long enough to cool the cushion ring back to below zero at -10 degrees C, if the helmet mounted earmuffs are placed in stand-by position. In the worst case this will cause 1.6 dB increase in daily exposure level to noise.
用于认证目的的听力保护器（HPD）的型式试验将在实验室室温下进行。可选择地，HPD的机械耐久性将通过跌落试验在寒冷环境中进行测试。本研究的目的是找出跌落试验的相关性、HPD防护性能的变化，并最终估计在寒冷环境中抗噪声保护效率的可能变化。总共选择了22个HPD进行测量：18个耳罩和4个安装在工业头盔上的耳罩。通过对处于寒冷环境中的测试对象应用插入损耗法来测量每个耳罩杯的衰减。使用30秒的间隔进行采样，跟踪缓冲环的衰减和温度变化长达9分钟。试验中有3个HPD损坏。两个耳罩和一个安装在头盔上的HPD中的可更换缓冲垫破裂。更换了可更换部件，并将出现连接故障的HPD从插入损耗测量中移除。在9个HPD中，相对变化小于3dB，最严重时为10dB。这种变化通常发生在低频，当放置冷却后的HPD时，开始时为125Hz。在各种HPD中，使衰减达到平衡的时间从1.5分钟到8分钟不等。恢复情况取决于缓冲环的温度。在所有情况下，当缓冲环达到7摄氏度时，达到了完全衰减的温度。当在整个暴露期间始终使用HPD时，这种衰减的暂时降低对保护效率的影响较小。典型的一组林业工人的暴露会被打断。链锯必须加油，链条大约每40分钟需要磨锋利。在每天6小时的作业时间内，大约会有9至10分钟的休息时间，如果将安装在头盔上的耳罩置于备用位置，这段时间足以使缓冲环在-10摄氏度的环境中冷却回零度以下。在最坏的情况下，这将导致每日噪声暴露水平增加1.6dB。
