What are the adverse health effects of exposure to dust on the London Underground?
| ISRCTN | ISRCTN62140918 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN62140918 |
| ClinicalTrials.gov (NCT) | Nil known |
| Clinical Trials Information System (CTIS) | Nil known |
| Protocol serial number | P92035 |
| Sponsor | Imperial College London |
| Funder | Transport for London |
- Submission date
- 04/11/2021
- Registration date
- 08/11/2021
- Last edited
- 04/07/2024
- Recruitment status
- No longer recruiting
- Overall study status
- Completed
- Condition category
- Respiratory
Plain English summary of protocol
Background and study aims
The London Underground (LU) is the world’s oldest subterranean transport system. It normally provides 2.8 million journeys daily and employs around 20,000 staff. Those who travel and work on the LU are exposed to varying amounts of air pollution in the form of tunnel dust, also known as particulate matter (PM).
When PM is inhaled, it can cause health risks. While the health risks of PM in outdoor air have been studied extensively, the environment inside the LU is very different. Concentrations of PM in the LU are about 15 times higher than what can usually be found outdoors in London, and there are many metallic components, such as iron, due to friction between the wheels of the train and the rails, which are not normally seen with outdoor pollution. The potential health risks associated with tunnel dust in the LU have not been studied and are poorly understood.
The aim of our study is to develop a better understanding of the (short-term) health effects of exposure to LU tunnel dust. Here we propose a secondary data analysis of routinely collected sickness absence records for LU staff. Examining an occupational group such as this is a common – and potentially efficient - way of examining an issue with potentially wider public health impact. Workers tend to have higher exposures than the general public, making signals of concern more readily detected; conversely, an absence of harm in this group can be reassuring.
Who can participate?
Employees of the LU employed between 01/01/2014 and 31/12/2019, including those who have joined or left between this period.
What does this study involve?
Data collected from the LU Human Resources department will be used to analyse the frequency of sickness absence due to lung and heart illnesses. Selected participants may also be invited to wear a lightweight personal dust monitor to measure their exposure to PM throughout the working day.
What are the possible benefits and risks of participating?
The results of this study will allow us to better understand any potential occupational hazards employees may see during their work. It may lead to safer and cleaner working environments within the LU.
Where is the study run from?
Imperial College London (UK)
When is the study starting and how long is it expected to run for?
November 2021 to December 2023
Who is funding the study?
Transport for London (UK)
Who is the main contact?
Dr Johanna Feary, j.feary@imperial.ac.uk
Contact information
Scientific
Department of Occupational and Environmental Lung Disease
Imperial College (NHLI) and Royal Brompton Hospital
1b Manresa Road
London
SW3 6LR
United Kingdom
| j.feary@imperial.ac.uk |
Public
200 Buckingham Palace Road
London
SW1W 9TJ
United Kingdom
| luohme@tube.tfl.gov.uk |
Study information
| Primary study design | Observational |
|---|---|
| Study design | Dynamic retrospective cohort study |
| Secondary study design | Cohort study |
| Study type | Participant information sheet |
| Scientific title | The adverse health effects of exposure to dust on the London Underground |
| Study objectives | Variations in the rates of sickness absence from cardiorespiratory disease between groups of employees on the LU will reflect their relative exposures to underground particulate matter. |
| Ethics approval(s) | Approved 12/10/2021, Imperial College Research Ethics Committee (RGIT Office, Room 221, Medical School Building, St Mary's Campus, Imperial College London, London, W2 1NY, UK; +44 (0)20 7594 9484; rgitcoordinator@imperial.ac.uk), ref: 21IC7231 |
| Health condition(s) or problem(s) studied | Cardiorespiratory sickness absence |
| Intervention | This retrospective cohort study will use London Underground (LU)'s Human Resources (HR) electronic records, stored on the SAP (System Analysis and Software Development) database. Sickness absence records for all LU staff employed at any time between 01/01/2014 and 31/12/2019 inclusive will be assembled and given a unique project identification number. The HR records include position title which dictate the likely level of tunnel dust exposure for each employee and includes changes in job allowing for variations in exposure. Based on each employee's position title, job description, and location of work, employees who are judged to have similar exposure levels to particulate matter (PM) will be grouped into distinct exposure categories. Based on the exposure categories, a 'job exposure matrix' or JEM will be developed, based on each member of staff's exposure to dust. Alongside this process, a measurement campaign will be undertaken throughout the LU network to apply quantitative estimates of PM exposure to each exposure category. A series of stationary measurements will be undertaken on representative station platforms, gates, offices, and in drivers' cabins. Selected employees will be invited to wear a lightweight personal dust monitor throughout their working shift. The HR records include dates of each period of sickness absence and a code to denote the cause of the absence. The list of codes will be filtered appropriately to include cardiorespiratory illnesses. The total number of (uncoded) sickness absences for each employee will be used as an indicator of sickness absence behaviour. These data will be linked to HR records of employees' genders, age ranges, date of employment, and position titles. After the JEM has been constructed, and while the direct measurements are being made and modelled, statistical analyses of HR data will be undertaken. Cause-specific incidence rates for different cardiorespiratory illnesses will be used to make comparisons across different exposure categories, after making adjustments for age, sex, sickness absence behaviour, and year/season to establish whether there is an independent relationship between estimated exposure to tunnel dust and the risk of illness from respiratory or cardiac causes. |
| Intervention type | Other |
| Primary outcome measure(s) |
Cause-specific incidence rates for different cardiorespiratory illnesses in LU employees with exposures to different concentrations of PM are measured using sickness absence data from the LU HR database |
| Key secondary outcome measure(s) |
1. PM concentrations at different microenvironments throughout the LU network measured through the use of stationary and personal measurements over an employee's 8-hour shift |
| Completion date | 31/12/2023 |
Eligibility
| Participant type(s) | Healthy volunteer |
|---|---|
| Age group | All |
| Sex | All |
| Target sample size at registration | 10000 |
| Total final enrolment | 29744 |
| Key inclusion criteria | LU staff employed between 01/01/2014 to 31/12/2019, including those who joined or left in this period. |
| Key exclusion criteria | Non-TfL employees whose sickness absence data are not recorded in the LU employment database. |
| Date of first enrolment | 01/01/2014 |
| Date of final enrolment | 31/12/2019 |
Locations
Countries of recruitment
- United Kingdom
- England
Study participating centre
London
SW1W 9TJ
United Kingdom
Results and Publications
| Individual participant data (IPD) Intention to share | No |
|---|---|
| IPD sharing plan summary | Not expected to be made available |
| IPD sharing plan | The datasets generated during and/or analysed during the current study are not expected to be made available due to the use of sensitive personal data from Transport for London. |
Study outputs
| Output type | Details | Date created | Date added | Peer reviewed? | Patient-facing? |
|---|---|---|---|---|---|
| Results article | 01/03/2024 | 04/07/2024 | Yes | No | |
| Participant information sheet | Participant information sheet | 11/11/2025 | 11/11/2025 | No | Yes |
| Protocol file | version 2.0 | 11/10/2021 | 05/11/2021 | No | No |
Additional files
- 40632 Protocol v2.0 11Oct2021.pdf
- Protocol file
Editorial Notes
04/07/2024: Publication reference added.
07/12/2023: The following changes were made to the trial record:
1. The intention to publish date was changed from 31/12/2023 to 31/07/2024.
2. The total final enrolment was added.
16/12/2022: The following changes were made to the trial record:
1. The overall end date was changed from 31/12/2022 to 31/12/2023.
2. The scientific contact was changed.
05/11/2021: Trial's existence confirmed by Imperial College London REC.
