Hearing threshold levels among steel industry workers in Samut Prakan, Thailand

Figures & data

Table 1 General characteristics of the study subjects (N=93)

Characteristics	Mean ± SD	n (%)
Gender, male		93 (100%)
Age (years) (range =23–59 years)	41.67±9.69
≤40		40 (43%)
>40		53 (57%)
Duration of work in steel industry (years) (range =1–39 years)	13.99±9.88
<5		23 (24.7%)
5–9.99		17 (18.3%)
10–19.99		19 (20.4%)
20–29.99		29 (31.2%)
>30		5 (5.4%)
Noise exposure level (dB[A])	91.79	44 (47.4%)
	96.07	49 (52.6%)
Working hours/week	59.09±6.42
Use of HPDs (% of the time)	60.54±25.34

Abbreviation: HPDs, hearing protection devices.

Table 2 Hearing threshold level of subjects

HTLs, dB	Test frequency, Hz
	0.5k	1k	2k	3k	4k	6k	8k
Right ear
Median (Q1, Q3)	20 (15, 20)	15 (15, 20)	15 (10, 25)	20 (10, 25)	25 (20, 45)	25 (15, 40)	20 (10, 35)
Mean±SD	19.25±6.92	18.49±8.46	18.44±9.83	20.59±13.82	31.34±16.87	29.62±19.05	25.64±19.70
Hearing loss, N (%) (HTLs >25 dB)	3 (3.2)	9 (9.7)	9 (9.7)	20 (21.5)	46 (49.5)	44 (47.3)	30 (32.3)
Left ear
Median (Q1, Q3)	15 (10, 20)	15 (10, 20)	15 (5, 20)	10 (5, 20)	35 (25, 45)	25 (20, 40)	20 (10, 35)
Mean±SD	16.02±8.74	14.73±8.94	14.67±10.16	14.46±13.99	40.15±17.69	32.20±20.94	25.48±21.51
Hearing loss, N (%) (HTLs >25 dB)	7 (7.5)	5 (5.4)	9 (9.7)	17 (18.3)	60 (64.5)	46 (49.5)	34 (36.6)
Hearing loss for both ears	2 (2.15)	4 (4.3)	4 (4.3)	15 (16.13)	38 (40.86)	32 (34.40)	19 (20.43)

Abbreviation: HTLs, hearing threshold levels.

Figure 1 Mean of hearing threshold level among steel industry workers at different frequencies.

Figure 2 Mean of hearing threshold level among steel industry workers at different ages.

Figure 3 Mean of hearing threshold level among steel industry workers for different lengths of employment.

Table 3 Pearson’s chi-squared test for age and hearing threshold level of subjects (n=93)

Category	n (%) age of subject at		P-value (two-tailed)	n (%) age of subject at		P-value (two-tailed)
	≤25 dB HL (right ear)	>25 dB HL (right ear)		≤25 dB HL (left ear)	>25 dB HL (left ear)
Subject profiles and status of hearing threshold level at 4.0 kHz
Age (years)
20–30	13 (86.7)	2 (13.3)	0.012	10 (66.7)	5 (33.3)	0.009
30–40	11 (55.0)	9 (45.0)		9 (45.0)	11 (55.0)
40–50	16 (42.1)	22 (57.9)		11 (28.9)	27 (71.1)
50–60	7 (35.0)	13 (65.0)		3 (15.0)	17 (85.0)
Subject profiles and status of hearing threshold level at 6.0 kHz
Age (years)
20–30	13 (86.7)	2 (13.3)	0.026	10 (66.7)	5 (33.3)	0.062
30–40	11 (55.0)	9 (45.0)		14 (70.0)	6 (30.0)
40–50	17 (44.7)	21 (55.3)		15 (39.5)	23 (60.5)
50–60	8 (40.0)	12 (60.0)		8 (40.0)	12 (60.0)

Abbreviation: HL, hearing loss.

Table 4 Pearson’s chi-squared test for the length of employment and hearing threshold level of subjects (n=93)

Category	n (%) age of subject at		P-value (two-tailed)	n (%) age of subject at		P-value (two-tailed)
	≤25 dB HL (right ear)	>25 dB HL (right ear)		≤25 dB HL (left ear)	>25 dB HL (left ear)
Subject profiles and status of hearing threshold level at 4.0 kHz
Length of employment (years)
0–5	17 (73.9)	6 (26.1)	0.051	13 (56.5)	10 (43.5)	0.095
5–1 0	7 (41.2)	10 (58.8)		5 (29.4)	12 (70.6)
10–20	12 (60.0)	8 (40.0)		9 (45.0)	11 (55.0)
20–30	9 (28.4)	20 (71.6)		6 (20.6)	23 (79.4)
>30	2 (50.0)	2 (50.0)		0 (0)	4 (100)
Subject profiles and status of hearing threshold level at 6.0 kHz
Length of employment (years)
0–5	14 (60.9)	9 (39.1)	0.807	15 (65.2)	8 (34.8)	0.70
5–1 0	9 (52.9)	8 (47.1)		7 (41.2)	10 (58.8)
10–20	12 (60.0)	8 (40.0)		11 (55.0)	9 (45.0)
20–30	13 (46.1)	16 (53.9)		12 (41.1)	17 (58.9)
>30	1 (25.0)	3 (75.0)		2 (50.0)	2 (50.0)

Abbreviation: HL.

Table 5 Prevalence of hearing loss at PTA (0.5, 1, 2, and 3 kHz) and PTA (4 and 6 kHz) by years in employment (N=93)

Years of employment	Mean age (years)	Number of workers		Number of workers (%) with hearing loss at two indicators
				Low frequencies (0.5,1,2, and 3 kHz)	High frequencies (4, 6 kHz)
<5.0	31.78		23	7 (17.4)	17 (73.9)
5.0–9.9	36.00		17	9 (52.9)	14 (82.4)
10.0–19.9	44.05		20	7 (35.0)	14 (70.0)
20.0–29.9	48.89		27	9 (33.3)	26 (96.3)
>30.0	55.17		6	2 (33.3)	6 (100)
Total	41.24		93	34 (36.6)	77 (82.8)

Abbreviation: PTA, pure-tone threshold average.