Journal of Health and Safety at Work

Introduction: In the most industrial environment, workers are exposed to noise everyday. Exposure to this physical hazardous agent can cause immediate as well as delayed adverse effects. Cognitive performance decrement is one of the adverse effects of noise exposure which its main consequences is occupational accidents. This study attempted examine the effect of exposure to different levels of noise with harmonic indices of neutral, treble and bass on the cognitive performance.

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Material and Method: In this analytical-descriptive study, the cognitive tests were performed by 33 students, aged 23-35 years. During the tests, participants were exposed to three type of noise including neutral, treble and bass at 4 different levels of 45, 75, 85 and 95 decibels. In order to assess students cognitive performance, continuous performance test (CTP) software was employed, which investigated attrition and reaction time.

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Result: The results of this study revealed that exposure to neutral noises with Noise Harmonic Index (NHI) of +3dB at the frequency of 1000 Hz, the maximum percentage of attention (99.88 %) was belonged to Sound Pressure Level (SPL) of 95 decibels. Maximum percentage of attention due to exposure to the treble noise with NIH -105 dB at the noise frequency of 8000 Hz (100%) and bass noise with NIH of 407 dB at the frequency of 500 Hz (99.92%) were belonged to the SPL of 95 and 85 dBA, respectively. Moreover, the result showed that the effect of bass noise with NIH of 4.5 dB and frequency of 500 Hz on reduction of attention were more than treble noise with NIH of -105 dB and frequency of 8000 Hz. Under exposure to neutral noise with NIH of 3 dB and frequency of 1000 Hz, the longest reaction time (2.594 Second) was observed at the SPL of 85 dBA. The longest reaction time for treble noise with NIH of -105 dB and frequency of 8000 Hz (2.786 Second) and for the bass noises with NIH of 4.5 dB and frequency of 500 Hz (2.594 Second) were also belonged to the SPL of 85 and 75 dBA, respectively.

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Conclusion: The results showed that bass noises (frequency of 500 Hz) increased reaction time, in comparison with treble noises (frequency of 8000 Hz).

Introduction: Heat stress is one of the Hazardous physical agents in the workplace, which can cause impairment of cognitive performance. The current study aimed to evaluate the effect of different levels of heat stress on attention and reaction time in a laboratory condition.

Material and Method: This experimental study was done among 33 students included 17 males and 16 females. Mean age of the participants was 22.1(SD=2.3). Attention and reaction time parameters were evaluated using the continuous performance test and  reaction time measurement device respectivlely, after exposure to different heat levels (22°C and 37°C). Data were analyzed using ANOVA test and SPSS 20 software.  

Result: The results of tests attention and reaction time showed that the average of attention percentage was decreased and the average of reaction time increased by increasing the heat level, with a  statistical differences of  (P˂0.001) in both cases. Attention percent in terms of exposure to 22°C temperature was significantly higher than 37°C (P˂0.001). But, reaction time was significantly higher than with the exposure to 37°C temperature than 22°C (P˂0.001).

Conclusion: The results of this study showed that, heat by increasing reaction time and decreasing attention leading to an impairment  in the individual’s cognitive performances. Therefore, in jobs such as control rooms and various industries that need attention, concentration and quick reaction, it is necessary to consider and optimize the heat conditions in order to increase the level of attention and decrease of reaction time.