noise is one of the physical factors in industries , and , today , more attention is being paid to its harmful effects . after smoking and air pollution , noise pollution world health organization ( who ) also considers noise as the third dangerous pollutant of megacities . moreover , damage to the hearing system , interference in conversation , effects on the organs of vision , effects on balance system , social disorders , psychological as well as nervous effects , impacts on electrolytes , physiological effects , and mental effects are among the noise health effects on human body . almost two thousand years ago , pliney stated that the individuals living near noisy waterfalls tend to suffer from hearing loss sooner than other people . the results of a study which was conducted in 2000 showed hearing loss as the main harmful effect of long exposure to occupational noise . furthermore , neghab et al . performed a study on the workers of petrochemical complex and revealed that noise had led to an increase in blood pressure and hearing loss in the exposed workers . in the same line , smith et al . investigated the body 's physiological responses when being exposed to high - noise levels and showed that exposure to repeated , continuous noise caused the incidence of physiological as well as psychological responses and resulted in changes in heart rate as well as blood pressure [ 6 , 7 ] . moreover , according to the study by motamedzade and ghazaiee , exposure to higher than 85  db noise levels increased both systolic and diastolic blood pressure , affected the working efficiency , and led to interference in conversation . ising and michalak compared the effects of noise in both field and laboratory conditions and showed that exposure to 97  db noise level had resulted in physiological as well as psychological changes in half of the study subjects . overall , according to the report by who , noise causes 4 million dollars health damage every day [ 10 , 11 ] , and occupational noise can put the industrial workers ' health at a high risk . based on what was mentioned above and since noise can have both physiological and psychological effects on humans , the present study was conducted in order to investigate the effects of noise exposure on blood pressure and heart rate in steel industry . the present cross - sectional study aimed to investigate the effect of occupational noise exposure on heart rate and systolic as well as diastolic blood pressure . considering ci = 95% and power of 90% , the sample size of the study was determined as 50 subjects who were selected through simple random sampling . the inclusion criteria of the study were being physically and psychologically healthy , not smoking , not using alcohol , not taking hypnotic drugs , and not working in shifts . the participants ' demographic information was gathered through a questionnaire , and their systolic as well as diastolic blood pressure and heart rate were measured using beurer bc16 pulse meter . in addition to assessing the workplace noise , a sample of the devices ' noise was also obtained . in doing so , a microphone was attached to a worker 's collar near his ear and the device 's noise was recorded for 10 minutes . considering the features of steel industry , this study was conducted with exposure to 85 , 95 , and 105  db noise levels in controlled experimental conditions for 3 consecutive days . at first , the subjects were placed in a quiet room with the background noise level of 40  db and their systolic as well as diastolic blood pressure and heart rate was measured . then , they were exposed to the noise recorded from the workplace at 85 , 95 , and 105  db levels for 5 minutes and systolic as well as diastolic blood pressure and heart rate was measured again . in order to eliminate the sequence effect , the experiments were performed with 24  h intervals . finally , the data were entered into the spss statistical software , and paired t - test was used in order to compare the means of the variables before and after noise exposure . the demographic characteristics of the study subjects are presented in table 1 . in this study , age , weight , height , systolic and diastolic blood pressure , and moreover , the results of workplace noise analysis showed that , among the 60 areas under study , 13 ( 23% ) had over 85  db noise level and 23 ( 39% ) had caution range noise level , that is , 6585  db . table 2 presents the subjects ' systolic as well as diastolic blood pressure and heart rate before and after noise exposure in the controlled experimental conditions . as the table depicts , the mean of systolic blood pressure has increased at all noise levels except for 85  db ; however , the changes were not statistically significant ( p > 0.05 ) . on the other hand , diastolic blood pressure increased a little at all the three noise levels . besides , a decrease was observed in the mean of heart rate at all the noise levels ; nevertheless , the changes were not statistically significant ( p > 0.05 ) . up to now , the mechanism noise that affects blood pressure has not been identified . nevertheless , several studies have shown high secretion of vasoconstrictors in urine as a result of being exposed to higher than 90  db noise levels , which might represent the biological effects of noise exposure on blood pressure . in the study by ising and michalak no significant difference was observed in the subjects ' heart rate after acute noise exposure . in general , acute exposure to 90100  db noise levels increases the catecholamines [ 5 , 13 ] which might have led to an increase in systolic as well as diastolic blood pressure . however , the changes in blood pressure were not statistically significant , which is consistent with the findings of the present study . on the other hand , motamedzade and ghazaiee showed that exposure to higher than 85  db noise levels resulted in an increase in both systolic and diastolic blood pressure , affected the working efficiency , and led to interference in conversation , which is in line with the results of the current study . in the study by neghab et al . , a significant difference was found between the exposed and the reference groups ' mean blood pressure , which might be due to the industry under investigation as well as the study design . moreover , the exposed and the reference groups were similar in the present study , while neghab et al . selected two separate groups ( control and exposed ) in order to investigate the effects of noise . overall , since blood pressure and heart rate might be affected by various factors , the results obtained regarding the effects of noise exposure on these parameters must be interpreted with caution . the findings of the present study were in agreement with those of the previous studies conducted on the issue . according to the results , no significant difference was observed in blood pressure and heart rate before and after acute exposure to 85 , 95 , and 105  db noise levels .