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Diss Factsheets

Toxicological information

Direct observations: clinical cases, poisoning incidents and other

Administrative data

Endpoint:
direct observations: clinical cases, poisoning incidents and other
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2-5 months
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP, non-guideline human experimental study, published in peer reviewed literature, limitations in design but otherwise adequate for assessment

Data source

Reference
Reference Type:
publication
Title:
Low personal exposure to benzene and 1,3-butadiene in the Swedish petroleum refinery industry
Author:
Almerud P
Year:
2017
Bibliographic source:
International archives of occupational and environmental health 90.7 (October 2017): 713-724.

Materials and methods

Study type:
study with volunteers
Endpoint addressed:
other: Occupational exposure
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
505 repeated personal exposure measurements were performed among workers at 2 swedish refinaries. Mean levels were calculated using mixed-effects models, and a large fraction of measurements below limit of detection required imputation of computer-generated data.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Benzene
EC Number:
200-753-7
EC Name:
Benzene
Cas Number:
71-43-2
Molecular formula:
C6H6
IUPAC Name:
benzene
Test material form:
not specified
Details on test material:
Common name: Benzene
No other data provided
Specific details on test material used for the study:
Test material was occupational exposure as part of working in a petroleum refinery.

Method

Type of population:
occupational
Subjects:
Workers at Swedish petroleum refinaries. They were further subdivided into different exposure groups based on their occupation on site.

Outdoor process technicians: Supervising process operations in the process area and in the harbour and tank park, working mainly outdoors. The tasks are infrequent and of short duration, except for routine work such as sampling and inspections performed on a daily basis. Also spending part of the work shift in a control room

Process area: Supervising operations in the process area, putting equipment into or taking it out of operation, taking product samples and performing minor maintenance work

Harbour and tank park: Supervising work performed in the harbour (only at Refinery 1), such as coupling and uncoupling hoses. Tasks performed in the tank park include drainage of water from tanks, taking samples and tank gauging

Indoor process technicians: Supervising process operations (in the process area and in the harbour and tank park) from a control room

Outdoor maintenance workers: Performing equipment maintenance/repairs on refinery units. Workers in this group include pipe fitters, welders, instrument technicians, electricians and mechanics

Process area: Performing tasks on refinery units in the process area

Harbour and tank park: Performing tasks on refinery units in the harbour and tank park

Indoor maintenance workers: Performing maintenance work, mainly in indoor tool shops

Laboratory workers: Performing analyses of process streams and other laboratory work including collection of samples

Engineers: Monitoring the process operations. Responsible for the design of the refinery processes and mechanical functions

Safety and emergency staff: Responsible for internal safety and emergency service, performing rescue operations, area measurements, and routine inspections and providing personal protective equipment

Inspectors: Performing inspections of refinery units

Administrative personnel: Administrative and executive personnel working at the main office

Railroad terminal workers: Responsible for loading products such as liquified petroleum gas (LPG) on to railroad tank cars and performing work in the tank farm
Ethical approval:
not specified
Route of exposure:
inhalation
Reason of exposure:
intentional, occupational
Exposure assessment:
measured
Remarks:
Fo fractions below below limit of detection, computer-generated information was used.
Details on exposure:
Representative samples of occupational exposure.
Examinations:
The measurement strategy included different exposure groups consisting of refinery workers with similar estimated exposure to benzene. The a priori assessment of the exposure was performed in close cooperation with the study team and resulted in exposure groups based mainly on a combination of occupation and work tasks. At least five workers were randomly selected from each of the a priori formed exposure groups and personal measurements were performed over a full work shift on randomly selected days. Repeated measurements were, as far as possible, performed on two sampling occasions spread over a time period of 2–5 months. This resulted in at least ten repeated measurements within each exposure group. The measurements were performed over three shifts at Refinery 1 and over two shifts at Refinery 2, with up to 15 workers (randomly selected by one of the researchers) from different exposure groups and shifts sampled during the same day. In addition, a number of samplers for “worst case” measurements (i.e. work shifts with assumed high exposures to benzene and/or 1,3-butadiene) were available at Refinery 1 upon request by the workers. Results of the worst case measurements were not included in estimations of average exposure.

In total, 505 personal benzene and 1,3-butadiene samples (348 samples at Refinery 1 and 157 at Refinery 2) were collected on 265 randomly selected workers (178 and 87 at Refinery 1 and 2, respectively) from the different a priori formed exposure groups (Table 1). The measurements were carried out during 41 full work shifts in the spring and autumn of 2009 at Refinery 1, and during 34 shifts in the spring of 2010 and the autumn of 2010 and 2011 at Refinery 2. At Refinery 1, the median sampling times were 8 h (range 3.5–13 h) during weekdays and 12 h (range 10–13 h) during weekends, when the work shifts were generally longer. At Refinery 2 the median sampling time was 7 h (range 4.7–9.1 h).
Medical treatment:
Not examined

Results and discussion

Clinical signs:
Not examined
Results of examinations:
The average (AM) personal benzene exposure among process technicians was 15.3 μg/m3 (95% CI 10.4–22.5 μg/m3) at Refinery 1, and 13.7 μg/m3 (95% CI 8.3–22.7 μg/m3) at Refinery 2 (Table 2). At Refinery 1, measurements were performed on both process technicians working indoors supervising the process from a control room, and process technicians working mainly outdoors. At Refinery 1 the outdoor process technicians had statistically significant higher exposure compared with indoor process technicians (AM 20.7 versus 3.7 μg/m3, p < 0.05 for the difference in GM). Among the outdoor process technicians working in the oil harbour and tank park (only Refinery 1) the benzene exposure was higher compared with those working in the process area (74.5 versus 9.6 μg/m3), and the difference in GM was almost statistically significant (p < 0.10). At Refinery 2, no significant difference was found between process technicians working in the process area and process technicians working in the tank park (Table 2). The average personal benzene exposure of maintenance workers (only Refinery 1) was significantly lower compared with that of outdoor process technicians (5.9 versus 20.7 μg/m3, p < 0.01 for GM) (Table 2). No statistically significant difference in benzene exposure was found between maintenance workers in the process area and maintenance workers in the harbour and tank park (Table 2). Personal
mean benzene exposure among laboratory workers, engineers, and safety and emergency staff (the last group only at Refinery 1) was between 4.5 and 8.4 μg/m3 (Table 2). Comparisons of exposure to benzene between similar exposure groups at the two refineries (process technicians working in the process area and laboratory workers) showed no statistically significant differences.
For most of the exposure groups above, more than 50% of the total variance in benzene exposure was attributed to within-worker variability, i.e. day-to-day variability (63– 97%) (Table 2). However, for laboratory workers at Refinery 2, the between-worker variability dominated (77%). For the other occupational exposure groups—indoor maintenance workers, inspectors and administration personnel at Refinery 1 (69 samples), and maintenance workers, inspectors and railroad terminal workers at Refinery 2 (63 samples)—the average benzene exposure was low, with only a minor fraction of samples above the LOD (data not shown).

Correlations between benzene and 1,3‑butadiene

Although the mean personal 1,3-butadiene exposures were ten to 100-fold lower than the benzene exposure levels measured at the same time, the two exposures were significantly correlated. The association between the benzene and the 1,3-butadiene exposure among process technicians working outdoors was estimated to be about rs = 0.38–0.40 at both refineries (at Refinery 1, rs = 0.39 when using all (n = 108) samples and rs = 0.41 when using only samples above the LOD (n = 38); and at Refinery 2, rs = 0.34 (n = 66) and rs = 0.42 (n = 19), respectively)

Exceedance of occupational exposure limits and the project‑specific guideline limit: identified tasks with increased exposure and worst case measurements

In total, only one sample at Refinery 1 exceeded the OEL for benzene, of 1500 μg/m3, and another two samples exceeded the project-specific guideline limit of 300 μg/m3. The measurement exceeding the OEL (3800 μg/m3) was taken during normal work by a process technician in the harbour, and the two samples exceeding the project-specific guideline limit were associated with work performed by a maintenance worker and a process technician in the tank park involving drainage operations (1300 and 360 μg/m3, respectively). At Refinery 2, only one sample (274 μg/m3) was close to the project-specific guideline limit and was associated with work performed by a process technician in the tank park. Additionally, a benzene exposure of 200 μg/m3 was recorded in a railroad terminal worker during a work shift when loading LPG on to a railroad tank car.

Workers at Refinery 1 could request worst case measurements separately from the measurements based on random selection presented above. These were requested by ten workers: six process technicians working outdoors in the process area, two process technicians working outdoors in the harbour and tank park, and two maintenance workers working in the process area. In some of these cases, the sampling period, median 6.9 h (range 4.2–9.2 h), did not cover a whole work shift. The process technicians (N = 8) had an AM personal benzene exposure of 85.8 μg/m3 and a median of 19 μg/m3 (range 7.0–350 μg/m3). One measurement, of 350 μg/m3, exceeded the project-specific guideline value for benzene. This sample was taken on a process technician working in the process area that for a period of 30 min worked with opening and drainage of a process unit containing isomerate (a petroleum product from an isomerization reaction). This kind of work task is performed less than once a month at the refinery. The AM and median 1,3-butadiene exposure among the process technicians was 14.3 and 2.1 μg/m3 (range
Effectivity of medical treatment:
Not examined
Outcome of incidence:
Not examined

Any other information on results incl. tables

Mean conditions of exposure

The median outdoor temperature during the measurements (measured as median of the average temperature during each work shift) at Refinery 1 was 9.8 °C (range −2.0 to 21 °C) and the median wind speed was 4.7 m/s (1–14 m/s). At Refinery 2, the median temperature during measurements was 14.5 °C (8.5–17.5 °C) and the median wind speed was 5.5 m/s (2.5–10.5 m/s). Precipitation was recorded in 37 and 36% of the measured work shifts at Refinery 1 and 2, respectively. The refinery workers spent an average of between 1 and 60% of their work shift outdoors (Table 1). Very few workers (1%) at the two refineries reported that they had used protective equipment, such as respiratory protection masks, during any task of their measured work shift.

Table 1Thea prioridefined exposure groups at Refinery 1 and 2, description of tasks performed during a typical work shift, and the average time spent outdoors expressed as percentage of the work shift

 

Exposure groups

Description of tasks

Average time spend outdoors (%)a

Refinery 1

Refinery 2

Outdoor process technicians

Supervising process operations in the process area and in the harbour and tank park, working mainly outdoors. The tasks are infrequent and of short duration, except for routine work such as sampling and inspections performed on a daily basis. Also spending part of the work shift in a control room

60

51

Process area

Supervising operations in the process area, putting equipment into or taking it out of operation, taking product samples and performing minor maintenance work

60

52

Harbour and tank park

Supervising work performed in the harbour (only at Refinery 1), such as coupling and uncoupling hoses. Tasks performed in the tank park include drainage of water from tanks, taking samples and tank gauging

60

47

Indoor process technicians

Supervising process operations (in the process area and in the harbour and tank park) from a control room

7

nab

Outdoor maintenance workers

Performing equipment maintenance/repairs on refinery units. Workers in this group include pipe fitters, welders, instrument technicians, electricians and mechanics

41

50

Process area

Performing tasks on refinery units in the process area

37

nab

Harbour and tank park

Performing tasks on refinery units in the harbour and tank park

54

nab

Indoor maintenance workers

Performing maintenance work, mainly in indoor tool shops

20

nab

Laboratory workers

Performing analyses of process streams and other laboratory work including collection of samples

1

2

Engineers

Monitoring the process operations. Responsible for the design of the refinery processes and mechanical functions

9

11

Safety and emergency staff

Responsible for internal safety and emergency service, performing rescue operations, area measurements, and routine inspections and providing personal protective equipment

37

nab

Inspectors

Performing inspections of refinery units

31

10

Administrative personnel

Administrative and executive personnel working at the main office

11

nab

Railroad terminal workers

Responsible for loading products such as liquified petroleum gas (LPG) on to railroad tank cars and performing work in the tank farm

nab

68

 

aInformation from questionnaires collected from each measured work shift

bNot applicable; exposure group not present/not sampled at refinery

 

Table 2Personal exposures to benzene (μg/m3) at Refinery 1 and 2

Exposure group

n/N

% > LOD

μX

95% CI

Max

μY

σ2/Y

σ2/bY (%)

σ2/wY (%)

Refinery 1

Refinery process technicians

68/132

42

15.3

10.4-22.5

3775

1.6

2.2

18

82

Outdoor process techniciansa,b

59/108

48

20.7

12.7-33.6

3775

1.7

2.6

22

78

Process area

40/71

44

9.6

6.4-15.5

144.1

1.5

1.6

9

91

Harbour and tank park

19/37

57

74.5

34.6-160.5

3775

2.2

4.1

20

80

Indoor process techniciansa

14/24

17

3.7

3.0-4.5

7.9

1.2

0.2

19

81

Maintenance workersb

34/67

22

5.9

3.7-9.4

1324

0.9

1.8

14

86

Process area

21/41

20

3.6

2.7-4.9

16.7

1.0

0.6

15

85

Harbour and tank park

10/20

25

13.3

5.9-30.3

1324

1.1

3.1

11

89

Laboratory workers

13/25

32

4.6

3.4-6.2

15.4

1.3

0.4

16

84

Engineers

31/41

27

4.5

3.0-6.7

45.6

1.0

0.9

25

75

Safety and emergency staff

7/14

43

5.1

3.9-6.6

9.9

1.5

0.2

24

76

Refinery 2

Outdoor process technicians

45/66

47

13.7

8.3-22.7

273.6

1.6

2.1

11

89

Process area

35/51

45

13.3

7.5-23.8

159.4

1.6

2.1

18

82

Tank park

10/15

53

15.8

5.1-48.4

273.6

1.7

2.2

3

97

Laboratory workers

6/11

45

8.4

3.4-20.7

20.0

1.7

0.9

77

23

Engineers

9/17

29

5.0

2.5-9.7

29.9

1.1

1.0

37

63

 

n number of workers, N number of measurements, % >LOD percentage of samples above the limit of detection (LOD), μX arithmetic mean (AM), calculated as exp(μY + σ2/Y /2) where μY and σ2/Y are the mean and the variance of the log-transformed observations, CI confidence interval for the AM, Max maximum level detected, μY and σ2/Y mean and variance of the log-transformed observations, σ2/bY and σ2/wY between- and withinindividual variance of the log-transformed observations a Significant difference in geometric mean (GM) between outdoor and indoor process technicians, p < 0.05, at Refinery 1 b Significant difference in GM between outdoor process technicians and maintenance workers, p < 0.01, at Refinery 1

Applicant's summary and conclusion

Conclusions:
Refinery workers in the Swedish petroleum refinery industry have a low average personal exposure to benzene and 1,3-butadiene. Mean exposures are well below the Swedish OELs, with levels of about 1% of the OEL for benzene and even lower levels for 1,3-butadiene. A large fraction of the measurements were below the LOD. We used computer-generated data to provide valid estimates of the mean personal exposure for exposure groups with more than about 15% of measurements above the LOD. The close cooperation with the refineries during this study resulted in interventions (e.g. improved instructions for use of personal protective equipment) and increased the knowledge about occupational exposure to benzene and 1,3-butadiene at the refineries. This study provides exposure data that can serve as a basis for an exposure assessment in future research on mortality and cancer incidence in the Swedish petroleum industry.
Executive summary:

Purpose Petroleum refinery workers are exposed to the carcinogens benzene and 1,3-butadiene. Declining exposures have been reported internationally but information on current exposure in the Swedish refinery industry is limited. The aim was to examine refinery workers’ personal exposure to benzene and 1,3-butadiene and increase awareness of exposure conditions by collaboration with involved refineries.

Methods Altogether 505 repeated personal exposure measurements were performed among workers at two refineries. Full-shift measurements were conducted in different exposure groups using Perkin Elmer diffusive samplers filled with Carbopack X. Mean levels were calculated using mixed-effects models. A large fraction of measurements below the limit of detection (LOD) required imputation of computer-generated data.

Results Mean benzene exposure among process technicians was 15.3 μg/m3 (95% CI 10.4–22.5 μg/m3) and 13.7 μg/m3 (95% CI 8.3–22.7 μg/m3) for Refinery 1 and 2, respectively. Process technicians working outdoors had higher exposure than maintenance workers (20.7 versus 5.9 μg/m3, p < 0.01). Working in the harbour and tank park (Refinery 1), compared with the process area, was associated with higher exposure. The 1,3-butadiene exposure was low, 5.4 and 1.8 μg/m3, respectively. The total variation was

generally attributed to within-worker variability.