Search

The goal of this project was to assess the impact that sleeper berth usage has on operator alertness. Forty-seven males and nine females participated in this study, constituting 13 teams and 30 single drivers. All drivers who participated in this study were recruited from one of four for-hire commercial trucking companies. Two tractors, a 1997 Volvo L4 VN-series tractor and a 1995 Peterbilt 379, with functionally identical instrumentation packages and data collection systems, were used for the study. The data acquisition system functioned to record four camera views, including the drivers face; driving performance information, including steering, lane departure, and braking; sleeper berth environmental data, including noise, vibration, and temperature; subjective alertness ratings; and data from the Nightcap sleep-monitoring system. The following results were obtained: (1) Sleeping in either a stationary or moving sleeper berth was shown to adversely affect sleep quality and quantity when compared to the home sleep data. This was particularly true for team drivers in moving trucks. (2) Team drivers generally acquired more sleep (greater than one hour per day on average) than did single drivers, with single drivers reporting six hours of sleep per 24-hour period and team drivers reporting just over seven hours per 24-hour period. (3) Team drivers had significantly more sleep disturbances than did single drivers. A primary cause of these disturbances appeared to be noise and vibration present in the sleeper berth of a moving truck. (4) In general, single drivers were rated as not drowsy more often and team drivers, who were rated as somewhat drowsy or moderately drowsy more often. However, of the 20 very/extremely drowsy episodes captured by Observer Ratings of Drowsiness, 16 were from single drivers. (5) Single drivers had many more critical incidents at all levels of severity relative to team drivers. (6) The frequency of critical incidents and driver errors varied significantly by the Hour of Day. However, many more incidents occurred during the afternoon and early evening as opposed to late at night. (7) Single drivers were more alert in the morning and gradually become fatigued during the day, whereas team drivers maintained a relatively constant level of alertness throughout the 24-hour clock. United States. Federal Motor Carrier Safety Administration Contract No. DTFH61-96-C-00068

The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremely important industrial safety issue. International standard ISO 773 1—1986(E), Danger Signals for Work Places — Auditory Danger Signals, requires that any auditory alarm or warning be audible to all individuals in the workplace, including those suffering from a hearing loss and/or wearing hearing protection devices (HPDs). Very little research has been conducted to determine how an individual's hearing level affects his/her ability to detect an auditory alarm or warning in a high-noise environment while wearing an HPD. The research effort described herein was undertaken to determine how the ability to detect an alarm or warning signal changed for individuals with normal hearing and two levels of hearing loss as the levels of masking noise and alarm were manipulated. Pink noise was used as the masker since it is a generally-accepted, generic substitute for industrial noise. A heavy-equipment reverse alarm was used as the signal since it is a common alarm in industrial facilities and construction sites. The rating method paradigm of signal detection theory was used as the experimental procedure in order to separate the subjects’ absolute sensitivities to the alarm from their individual criteria for deciding to respond in an affirmative manner. Results indicated that even at a fairly low signal-to-noise ratio (0 dB), individuals with a substantial hearing loss [a pure-tone average (PTA) hearing level on the order of 45-50 dBHL in both ears] are capable of hearing the alarm while wearing a high-attenuation earmuff. Predictive models were developed using nonlinear regression techniques. These models may be used to predict whether or not individuals with known hearing levels will be capable of hearing the alarm under known conditions or to determine the level of alarm presentation in order to be heard reliably by individuals with a specified range of hearing for given noise levels Ph. D.

An experiment was conducted to determine the effects of different acoustic characteristics of the testing environment on the measured attenuation of hearing protection devices (HPDs) when using a standard real-ear attenuation at threshold (REAT) protocol. In the experiment, three earmuffs and three earplugs were tested in two diffuse sound fields implemented in two different sound environments with different loudspeaker configurations. In the first case, the testing environment was reverberant, with frequency-specific reverberation time characteristics as specified in ANSI $3.19- 1974, "Method for the Measurement of Real-Ear Protection of Hearing Protectors and Physical Attenuation of Earmuffs" and with three loudspeakers, one in each principal plane of the room. In the other case, a diffuse sound field was established within an anechoic chamber (free-field), as permitted by ANSI S12.6-1984 "Method for the Measurement of the Real-Ear Attenuation of Hearing Protectors" using four loudspeakers, one at each vertex of a tetrahedron with the subject's head center position at the centroid. Each of the environments met the requirements of the applicable ANSI standard as well as the requirements of standards adopted by several foreign countries. The experimental design allowed a direct comparison of the testing environments (reverberant vs. free-field) permitted by the two aforementioned ANSI standards. Results indicate that for both earmuffs and earplugs, the environment in which a REAT evaluation is performed has a statistically significant impact on the results of the evaluation. These results have implications for ongoing standards development efforts not only in the United States but also abroad since the testing environments investigated in this research are either required or allowed by several international standards. These international standards include: International Standard ISO 4869-1981, Canadian Standard CSA Z94.2-M1984, British Standard BSI 5108:1983, and Swedish Standard SS 882151 (1981). The impact of outlier dismissal on the results of REAT tests of HPDs was also investigated and found to have minimal impact on the results obtained in this experiment. However, this result is most likely case-specific and it is doubted that any generalizations can be made concerning outlier tests and their impact on HPD evaluations. As a side issue, it was also determined that ear canal size is highly correlated with attenuation achieved using premolded earplugs with attenuation decreasing with increasing ear canal size. No consistent gender effects were found in the analysis, indicating that gender alone may not be an important factor in determining how much attenuation can be obtained with a given HPD. Finally, the lack of a significant trial effect points to the absence of a strong practice effect over the three trials of a REAT evaluation, at least for subjects who are highly practiced in the REAT procedures. Master of Science