Bus-exposure matrix, a tool to assess bus drivers' exposure to physicochemical hazards

Swiss bus drivers suffer from musculoskeletal disorders, fatigue, and stress and have an excessive mortality from lung cancer and suicide compared to other workers. However, their occupational exposure is poorly documented. We created a bus-exposure matrix (BEM) to determine occupational exposures to 10 types of physical-chemical hazards for 705 bus models used in Switzerland since 1980. For this, we made a comprehensive bus inventory and review of 50 technical characteristics of each bus model, identified 10 bus models representative of the Swiss bus fleet evolution, and conducted static and dynamic exposure measurement campaigns in the representative buses. The measured values were then extended to the entire fleet using Integrated Nested Laplace Approximation (INLA) models. The choice of predictors and technical bus characteristics included in the models were based on directed acyclic graphs. To demonstrate the usefulness of the BEM as an exposure assessment tool, we used data from the 2022 survey of Swiss bus drivers who listed the bus models they had driven during their careers. The BEM linkage with these bus drivers' histories enabled us to estimate annual exposure to PM10 ratio (-), ultrafine particle ratio (-), whole-body vibration (m/s2), floor vibration (m/s2), equivalent noise (dB(A)), peak noise (dB(C)), high-frequencies electric fields (V/m), low-frequencies magnetic field (µT), low-frequencies electric fields (V/m), and air exchange rate (1/h) of 809 Swiss bus drivers. Historical data assessment from 1985 through 2022 showed that peak noise, high- and low-frequencies electric field levels have increased, while PM10 ratio, ultrafine particle ratio, equivalent noise, whole-body vibration levels, and air exchange rate have decreased. This, first in the world, BEM is an original tool for retrospective exposure assessment that will enable further research in the occupational health of bus drivers.