This study used data from the 4th Korean Working Conditions Survey (KWCS), which was conducted between June and September 2014 on employed workers by the Occupational Safety and Health Research Institute (OSHRI) affiliated under the Ministry of Employment and Labor. The KWCS selected individuals who satisfied criteria for the definition of “economically active population” conducted one-on-one interviews at their home by a professional interviewer. The total sample of 50,007 persons, 15 years or older participated in this survey. The data used in this study are from 49,674 respondents who answered the question “Are you exposed at work to tobacco smoke from other people?”

The dependent variable was assessed to evaluate the risk of exposure to SHS by a question, “Are you exposed at work to tobacco smoke from other people?” Respondents answered on a seven-point scale of SHS exposure frequency; the choices were (in terms of all of the working time), “all”, “almost”, “3/4”, “half”, “1/4”, “almost never”, and “never”. For chi-square test, exposure to SHS in workplace was categorized into 3 group; “over 1/4 workhours” (all ~ 1/4), “almost never” and “never”. For logistic regression exposure to SHS in workplace was categorized into 2 group; “over 1/4 workhours” (all ~ 1/4) or “less than 1/4” (almost never and never). The rate of exposure to SHS for more than 1/4 of workhours (ESQ rate) was used to compare the SHS exposure by independent variables.

Independent variables included information on gender (“male” and “female”), age group ( “≤ 39”, “40–49”, “50–59” and “≥ 60”), job status (“self-employed without workers”, “self-employed with workers”, “wage workers (employees)”, “unpaid family worker” and “other workers”), type of wage worker (“permanent workers”, “temporary workers” and “daily workers”), wage provider (“workplace”, “a dispatcher” and “service provider”), Company size as number of workers in workplace ( “≤ 49”, “50–299” and “≥ 300”), type of workplace (“employer's place of business”, “customer's place of business”, “in the case of transportation as cars”, “outdoor (construction, field/etc)”, “my home” and “others”), job category (“manager”, “specialist”, “technician and associate export”, “office worker”, “service worker”, “sales worker”, “experts in agriculture and forestry fishing”, “functional person and related person”, “machine operator and assembly worker”, “laborer” and “soldier”), and night working days in a month ( “≤ 9”, “10–19” and “≥ 20”).

The item designed to evaluate the experience of discrimination at the workplace was used as a variables for the effect of exposure to SHS. The question is “During the past 12 months, did you experience to discrimination at your workplace related to age, race, nationality, gender, religion, disability, sexual orientation, academic group, region of origin, or employment status?” Respondents answered to the question about discrimination with ‘yes' or ‘no'.

The occupational categories of respondents were classified according to the Korean Standard Classification of Occupation (KSCO by National Statistical Office) and classified into occupational groups (52 groups, classification code: 2 digits) and detailed occupation (415 groups, classification code: 4 digits).

Data were analyzed using PASW version 18.0 (SPSS Inc., Chicago, IL, USA). Weight is applied when conducting statistical analysis based on the results of the “economically active population survey (EAPS)” in 2014 conducted by National Statistical Office. A chi-square test was carried out to determine whether there is a significant different between SHS exposure frequency by general and occupational characteristics and experience of discrimination at work and logistic regression analysis was carried out to identify the risk level of SHS exposure by variables.

The sample characteristics are described in Table 1. Of the total 49,674 respondents, 57.8% were male and 36.9% were under the age of 39 which was the largest age group. The number of wage workers was 36,156 (72.8%) and number of respondents to the question about “wage worker type” and “wage provider” were 35,913 and 35,389 respectively. Of the respondents, 76.0% were permanent (regular) workers, 16.9% were temporary workers, and 7.1% were daily workers, respectively. Of the respondents, 94.7% were provided wage from workplace. By the size of the workplace, 79.7% were employed at a workplace with less than 50 employees. In the major categories of occupation, the office workers were the largest, followed by the service workers, the sales workers, and the simple laborers.

From the chi-square test, the variables that showed significant differences in the exposure to SHS were gender, age, occupation status, wage provider, the size of the workplace, type of workplace, job category, whether to wear the personal protective equipment, and the number of night shifts. The rate of exposure to SHS for more than one quarter of working time (ESQ rate) was 16% for males and 6.9% for females. By age, the ESQ rate was highest in the 50s and by employment status, the ESQ rate was highest for self - employed with workers. Among the wage workers, the ESQ rate was highest for the daily workers, and in terms of the wage-payment method, the ESQ rate was highest for workers who were paid by service companies. In terms of the number of employees at workplaces, the ESQ rate was highest for the companies with less than 50 employees and by types of workplace, the ESQ rate was highest in outdoor work-places, such as construction sites and farms. By types of occupation, the ESQ rate was highest in the functional and related functional staff. The rate of SHS exposure was higher for workers wearing protective gear than for workers not wearing protective gear. A greater- number of night shifts also increased SHS exposure (Table 1).

According to the logistic regression analysis (Table 2), the risk of SHS exposure of males was 4.107 times (95% CI: 3.461 ~ 4.874) higher than that of females. By age groups, exposure for those in their forties was 1.551 times (95% CI: 1.348 ~ 1.785) and for those in their fifties were 1.529 times (95% CI: 1.319 ~ 1.772) more than for those under 39 years of age. In terms of the number of workers in the workplace, the risk of exposure to SHS in companies with less than 50 workers was 2.114 times (95% CI: 1.721 ~ 2.595) higher than that in companies with more than 300 workers and that of daily workers was 1.318 times (95% CI: 1.102 ~ 1.575) higher than that of regular workers. The risk of exposure to SHS for workers receiving wages from the service provider was 1.736 times higher than that for workers receiving wages at work. The risk of exposure to SHS for outdoor workers was 1.668 times higher than for those working at the employer's place of business.

Examining the degree of exposure to SHS in terms of experience of discrimination in the last 12 months in the workplace, showed that workers who have experienced discrimination at work because of age (adjusted OR 1.637, 95% CI 1.468~1.825), race (adjusted OR 1.850, 95% CI 1.459~2.347), nationality (adjusted OR 2.699, 95% CI 2.161~3.371), sex (adjusted OR 1.969, 95% CI 1.623~2.389), disability (adjusted OR 2.758, 95% CI 2.069~3.676), sexual orientation (adjusted OR 1.801, 95% CI 1.231~2.633), academic group (adjusted OR 1.271, 95% CI 1.119~1.443), place of origin (adjusted OR 1.657, 95% CI 1.384~1.984), or employment status (adjusted OR 2.010, 95% CI 1.770~2.283) were more exposed to SHS than the counterparts who are not experienced discrimination (Tables 3 and 4).

Occupational groups (classification code: 2 digits) by KSCO were analyzed and classified into 52 groups. Construction and mining-related occupations (49.5%), metal coremakers-related trade occupations (33.3%), and transport and machine-related trade occupations (31.4%) were the highest exposure groups for SHS at the workplace. Public and enterprise senior, legal and administration professional occupations (0.9%), education professional and related occupations (1.7%), and health, social welfare, and religion-related occupations (1.7%) were the lowest in exposure to SHS at the workplace (Table 5).

Specific jobs (classification code: 4 digits) by KSCO were analyzed and classified into 415 jobs. Of these, 151 jobs with 50 or more respondents were analyzed. The top 20 jobs for exposure to SHS for more than a quarter of working time are shown in Table 6. Concrete-reinforcing iron workers (53.7%), plasters (52%), construction and mining elementary workers (49.5%), construction plumbers (48.9%), and entertainment facilities workers (47.9%) were the highest SHS exposure jobs. Among the top 50 jobs, construction jobs accounted for about a dozen (Table 6).

In this study, we found that male workers in their 40s and 50s, workers employed in workplaces with fewer than 50 employees, daily workers, temporary workers, and people working at the customer's premises or working outdoors had a higher risk of exposure to SHS than the others. The Dutch study reported that workers who were male and low-educated were more likely to be exposed to SHS [8]. The German study reported the aspect of higher SHS exposure in younger age group, but this is dependent on the place of exposure, and exceptionally at workplace, 30–44 years had highest SHS exposure differ by the others such as home, bars, or the house of friend [9]. It is known that blue-collar workers and service workers are more likely to expose the higher rate of SHS occupationally than white-collar workers. These are serious concern because blue collar workers have exposed more often to chemical and dust and SHS related health problems can be synergistically effect with those hazards [10].

Also, we found workers who had experienced discrimination at workplace based on age, race, nationality, gender, disability, academic group, place of origin, or type of employment were more likely to experience a higher rate of exposure to tobacco smoke than were their counterparts who had not experienced discrimination. A recent study reported that exposure to discrimination based on age, academic group or employment status put the workers at a high risk of having a poor well-being [12]. Another study also reported an association between SHS and psychological well-being and emphasized the importance of reducing SHS exposure at the workplace [13]. From these studies, exposure to discrimination and SHS are both significantly more likely to induce a poor well-being than counterparts who were not exposed to discrimination and SHS.

The top ten occupations with the highest SHS exposure were construction and mining-related occupations, construction and mining-related trade occupations, metal coremakers-related trade occupations, wood and furniture, musical instrument, and signboard-related trade occupations, transport and machine-related trade occupations, transport and leisure services occupations, wood, printing and other machine-operating occupations, other technical occupations, and skilled forestry occupations, skilled fishery occupations. The least exposed occupations were public and enterprise senior officers, legal and administrative professions, education professionals, and health, social welfare, and religion-related occupations. Wortley et al. (2002) [8] compared the levels of serum cotinine in nonsmokers to assess the risk of SHS exposure based on NHANES III (1988–1994) and found that among 40 occupational groups, the geometric mean of serum cotinine was highest in the waiter and waitress group (0.47 ng/mL), among seven job categories, the geometric mean of serum cotinine was highest in the device operation, producer, and laborer (0.22 ng/mL). The research data related SHS exposure by occupation were rare to find, instead we can refer to the smoking rate by occupations. Based on the NHANES(National Health and Nutrition Examination Survey) III in the United States, 1988–1994, smoking rates by occupation showed that material-moving occupations, construction laborers, and vehicle mechanics and repairers had the highest smoking rate, whereas teachers and sales representatives reported that the rate of smoking was low [14]. Smith and Leggat (2007) [15] reported that by job category, smoking was most common among laborers and least common among professionals, managers, or administrators. Occupations with high smoking rates were very similar to occupations with high SHS rates in our study. Tobacco smoke represents an occupational hazard and a smoke-free environment is an essential component of a healthy and safe. Smith and Leggat [15] reported that smoking rates were higher among unemployed persons in many European countries like France, Italy, and Sweden, the United States and Australia, whereas in Japan, people who were currently employed actually had the higher smoking rates. These results can be affected by different working condition including job status and occupation of each country. Therefore it is necessary to analyze the smoking and SHS exposure rates in job status and occupation for each country.

The strength of this study is to analyze the SHS exposure by job status and occupations and identify the priority group to implement smoking ban policy and confirm the workplace smoking is an occupational health hazard and a smoking ban policy at the workplace is the best option to reduce SHS. But, the limitation of study is that in 4th KWCS data, participant's smoking status was not surveyed and we have not been able to identify how much SHS exposure is affected by whether or not participants are smokers.