The main research objective of the four articles comprising this dissertation was to
provide retrospective exposure information for a planned study on cancer in a cohort within
Norway’s offshore petroleum industry.
Background information on possible exposure was obtained through company visits,
including interviewing key personnel (n = 83) and collecting monitoring reports (n = 118) and
other relevant documents (n = 329). The collected material was used to identify relevant
carcinogens. Twenty-seven job categories were defined based on a previous questionnaire
administered to present and former offshore employees in 1998. Descriptions of products
containing known and suspected carcinogens, exposure sources and processes were extracted
from the collected documentation and the interviews of key personnel (Article II).
Exposure data on oil mist and oil vapour covered 37 drilling facilities and were analysed
by descriptive statistics and by constructing linear mixed-effects models (Article I).
A group of three university and five industry experts individually assessed the likelihood
(unlikely, possible or probable) of exposure for combinations of 17 carcinogens, 27 job
categories and four time periods (1970–1979, 1980–1989, 1990–1999 and 2000–2005). Each
rater was to assess 1836 combinations based on summary documents on carcinogenic agents,
which included descriptions of sources of exposure and products, descriptions of work
processes carried out within the different job categories and monitoring data. Interrater
agreement was calculated using Cohen’s kappa index and single and average score intraclass
correlation coefficients. Differences in interrater agreement between the different time
periods, raters, carcinogen class and amount of information provided were then studied
In subsequent plenary discussions, the experts agreed on exposed combinations.
Agreement between the individual and the panel assessments was calculated using Cohen’s
kappa index. Using the panel assessment as reference, sensitivity and specificity were
estimated (Article IV). Results:
This study indicated possible exposure to the following known and suspected
carcinogenic agents, mixtures or exposure circumstances: benzene; mineral oil – inhalation
exposure; mineral oil – skin exposure; crystalline silica; asbestos; refractory ceramic fibres;
formaldehyde; tetrachloroethylene; trichloroethylene; welding; nickel compounds;
chromium [VI]; lead; crude oil – skin exposure; diesel engine exhaust; dichloromethane;
ionising radiation; and occupational exposure as a painter (Article II). Monitoring reports
were obtained on seven agents: benzene, mineral oil mist and vapour, respirable and total
dust, asbestos fibres, refractory ceramic fibres, formaldehyde and tetrachloroethylene (Article
II). The arithmetic mean of 367 personal samples of benzene was 0.037 ppm (range: less than
the limit of detection – 2.6 ppm). Asbestos fibres were detected (0.03 fibres/cm3) when
asbestos-containing brake bands were used in drilling draw work in 1988. The personal
exposure to formaldehyde in the process area ranged from 0.06 to 0.29 mg/m3.
Samples of oil mist and oil vapour had been taken during the use of three generations of
hydrocarbon base oils: diesel oils (1979–1984), low-aromatic mineral oils (1985–1997) and
nonaromatic mineral oils (1998–2004). Sampling done before 1984 showed high exposure to
diesel vapour (arithmetic mean = 1217 mg/m3). Downward time trends were indicated for
both oil mist (6% per year) and oil vapour (8% per year) when the year of monitoring was
introduced as a fixed effect in a linear mixed-effects model analysis. Rig type, technical
control measures and mud temperature significantly determined exposure to oil mist. Rig
type, type of base oil, viscosity of the base oil, work area, mud temperature and season
significantly determined exposure to oil vapour. In these models major decreases in variability
were found for the between-rig components (Article I).
In the individual expert assessment overall, 336 (18%) of the 1836 combinations were
denoted possible exposure, and 253 (14%) scored probable exposure. Stratified on the 17
carcinogenic agents, the prevalence of probable exposure ranged from 3.8% for refractory
ceramic fibres to 30% for crude oil. The overall mean kappa (κ) was 0.42; single score
intraclass correlation coefficient was 0.62, and the average intraclass correlation coefficient
was 0.93. Providing limited quantitative measurement data was associated with less
agreement than for equally well-described carcinogens without sampling data.
The eight experts assessed 1157 (63%) of the 1836 combinations in plenary, resulting in
265 (14%) agreed exposed combinations. The agreement between the experts’ individual
assessments and the panel assessment was κ = 0.53–0.74. The sensitivity was 0.55–0.86 and specificity 0.91–0.97. For these parameters, there were no apparent differences between the
university experts and the industry experts.
For defined job categories in Norway’s offshore petroleum industry this study describes
possible exposure to known and suspected carcinogenic agents, mixtures or exposure
circumstances. An expert panel agreed on probable exposure for 265 of 1836 possible
combinations of 17 agents, 27 job categories and four time periods. Measurement data on
seven agents are presented. Benzene and mineral oil mist and vapour were considered to have
the best potential for development of quantitative estimates of exposure.
Exposure to oil mist and oil vapour declined over time in the mud-handling areas of
offshore drilling facilities. Exposure was associated with rig type, mud temperature, technical
control measures, base oil, viscosity of the base oil, work area and season.
The eight raters in the expert group seemed to have enough documentation on which to
base their individual estimates. However, providing limited monitoring data leads to more
incongruence among raters. The group was large enough to give reliable estimates.
The experts’ individual ratings highly agreed with the succeeding panel assessment. The
university experts and the industry experts’ assessments did not apparently differ.||en