An interventional study of Firefighting training exercises with no fire and Firefighting training exercises under wood fire in Reactive Hyperemia, Micro RNA and Heart Rate Variability, sponsored by National Research Centre for the Working Environment, Denmark. Completed at 2 sites in Denmark. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-08-06.
Sponsored by National Research Centre for the Working Environment, Denmark · Not applicable, Interventional, and Basic science
Epidemiological studies based on Danish registries have observed that Danish male firefighters have more cardiovascular disease, infertility diagnose and a trend to increased risk of cancer than other Danish employed males. Firefighting activities include a combination of stressors such as strenuous work under heat, smoke and soot known to be able to affect cardiovascular and reproductive health, with smoke and soot also being known to increase the risk of cancer.
The training facilities of real-fire extinguishing exercises in Denmark operate using wood or natural gas fire, which will have differential gradients of smoke, soot and possibly heat. The investigators will use different training conditions to create gradients of the different stressors and investigate health effects thereof. With this approach, the investigators expect to be able to evaluate the individual contribution of the different stressors in markers of cardiovascular, cancer and reproductive health risk. The project will include approx. 35 young conscript participants on a firefighting course, followed in four sessions, three firefighting training sessions under different fire conditions (no fire, wood fire and gas fire) and one control scenario.
The study methodology is based on a crossover design on firefighting training under different conditions, with characterization of exposure and assessment of cardiovascular, cancer and reproductive effect biomarkers. The study will be performed in cooperation with the Danish Emergency Management Agency.
The study will have one baseline session, while conscripts are in a classroom, and three sessions of firefighting-related exercises under different fire conditions, used currently in firefighting training programs in Denmark. The three firefighting training sessions will be controlled for equivalent work exercise using full protective gear and under different ambient conditions of firefighting training:
The order of the firefighting sessions will be as randomized as possible, and according to a selection of three sequence order options (no-wood-gas; wood-gas-no and gas-wood-no). Each campaign (corresponding to each rescue course) would desirably have one of these session sequences. It is not possible to blind the participants to the different scenarios, neither the field staff, but all the samples will be blinded for the subsequent laboratory analysis. The training sessions will have 1-3 weeks in between (accordingly with programmatic educational course schemes).
98 studies on the registry are indexed under Hyperemia; 44 are open to participants now.
This study's enrollment of 35 is below the median of 68 across 51 interventional studies indexed under Hyperemia.
Browse Hyperemia studies →National Research Centre for the Working Environment, Denmark is the lead sponsor of 23 studies on the registry; 1 is open to participants now.
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The participants will be volunteers (both males and females) recruited among conscripts in training in a desirable involved group up to 35 individuals.
Inclusion Criteria:
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Baseline measurements will be performed in the same schedule as measurements in the three other arms. In the baseline session, participants are in classroom before starting any firefighting exercise
Firefighting equivalent work, with exercises performed in a clean environment, without fire (no ambient temperature, soot or smoke). This type of exercise usually precedes or complements the training under real fire conditions.
Other: Firefighting training exercises with no fire
Firefighting under wood fire, with exposure to ambient heat, smoke and soot. This is the most common training scenario used in the training centres. The participants will be in teams performing pre-defined tasks (knocking down the fire, moving heavy objects, and searching and rescuing metal stand in models
Other: Firefighting training exercises under wood fire
Firefighting under gas fire, with exposure to ambient heat, and expectably less smoke and soot than with wood fire. These conditions are used in some Danish training centres, with logistical advantages (ease of turning or putting out the fire and managing the fire fuel) and unknown effect relating to exposure prevention (smoke and soot). The participants will be in teams performing pre-defined tasks (knocking down the fire, moving heavy objects, and searching and rescuing metal stand in models
Other: Firefighting training exercises under gas fire
The participants will be performing firefighting equivalent work in a clean environment, without fire (no ambient temperature, soot or smoke).
The participants will be in teams performing pre-defined tasks (knocking down the fire, moving heavy objects, and searching and rescuing metal stand in models), under wood fire conditions.
The participants will be in teams performing pre-defined tasks (knocking down the fire, moving heavy objects, and searching and rescuing metal stand in models), under gas fire conditions.
Change in reactive hyperemia index - afternoon
Reactive hyperemia index (RHI) measured with the device EndoPAT 2000. A reactive hyperemia is induced by a blood cuff on the upper arm and the peripheral vasodilation response is assessed in the small digital vessels of a fingertip with a portable device connected to a computer, with RHI determined by an algorithm from the device, with lower index values corresponding to a worsen situation.
Time frame: Baseline afternoon measurement, afternoon measurement immediately after firefighting without fire, afternoon measurement immediately after firefighting under wood fire and afternoon measurements immediately after firefighting under gas fire
Change in reactive hyperemia index - morning
Reactive hyperemia index (RHI) measured with the device EndoPAT 2000. A reactive hyperemia is induced by a blood cuff on the upper arm and the peripheral vasodilation response is assessed in the small digital vessels of a fingertip with a portable device connected to a computer, with RHI determined by an algorithm from the device, with lower index values corresponding to a worsen situation.
Time frame: Baseline morning measurement, morning measurement in subsequent day after firefighting without fire, morning measurement in subsequent day after firefighting under wood fire and morning measurement in subsequent day after firefighting under gas fire
Change in Heart Rate Variability pNN50 at rest - afternoon
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. pNN50 is the proportion of successive NN intervals differing by more than 50 milliseconds divided by the total number of N intervals (given in percentage).
Time frame: Baseline afternoon measurement, afternoon measurement immediately after firefighting without fire, afternoon measurement immediately after firefighting under wood fire and afternoon measurements immediately after firefighting under gas fire
Change in Heart Rate Variability pNN50 at rest - morning
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. pNN50 is the proportion of successive NN intervals differing by more than 50 milliseconds divided by the total number of N intervals (given in percentage).
Time frame: Baseline morning measurement, morning measurement in subsequent day after firefighting without fire, morning measurement in subsequent day after firefighting under wood fire and morning measurement in subsequent day after firefighting under gas fire
Change in Heart Rate Variability RMSSD at rest - afternoon
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. RMSSD is the square root of the mean squared differences of successive NN intervals (given in milliseconds)
Time frame: Baseline afternoon measurement, afternoon measurement immediately after firefighting without fire, afternoon measurement immediately after firefighting under wood fire and afternoon measurements immediately after firefighting under gas fire
Change in Heart Rate Variability RMSSD at rest - morning
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. RMSSD is the square root of the mean squared differences of successive NN intervals (given in milliseconds)
Time frame: Baseline morning measurement, morning measurement in subsequent day after firefighting without fire, morning measurement in subsequent day after firefighting under wood fire and morning measurement in subsequent day after firefighting under gas fire
Change in Heart Rate Variability ratio LF/HF at rest - afternoon
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. Ratio of low frequency and high frequency bands
Time frame: Baseline afternoon measurement, afternoon measurement immediately after firefighting without fire, afternoon measurement immediately after firefighting under wood fire and afternoon measurements immediately after firefighting under gas fire
Change in Heart Rate Variability ratio LF/HF at rest - morning
Heart rate variability (HRV) measured with the device EndoPAT 2000. The HRV is calculated using the initial 5.5 complete minutes before the cuff is applied. Ratio of low frequency and high frequency bands
Time frame: Baseline morning measurement, morning measurement in subsequent day after firefighting without fire, morning measurement in subsequent day after firefighting under wood fire and morning measurement in subsequent day after firefighting under gas fire
Changes in levels of 8-oxodG excretion in first morning urine
Oxidized nucleobase 8-oxodG will be measured in urine samples by High-performance liquid chromatography (HPLC) as marker of oxidative stress, together with creatinine, for adjusting for urine concentration. Data will be reported as nanomol 8-oxodG per millimol creatinine.
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in levels of DNA strand breaks in peripheral blood mononuclear cells
DNA strand breaks will be measured by comet assay, and reported as number of lesions per 10\^6 base pairs, transformed from percentage of DNA in tail using the calibration curve from the well-establish relationship between ionizing radiation dose and yield of strand breaks in DNA.
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in core temperature
Core body temperature will be assessed by an ingestible pill thermometer with data recorded and reported as time series during the period in transit.
Time frame: Baseline day, during the day of firefighting without fire, during the day of firefighting under wood fire and during the day of firefighting under gas fire.
Changes in scrotal temperature
Scrotal temperature will be assessed by skin sensor placed in the scrotum of male participants and reported as scrotal skin temperature time series.
Time frame: Baseline day, during the day of firefighting without fire, during the day of firefighting under wood fire and during the day of firefighting under gas fire.
Changes in scrotal thermoregulation
Core body temperature will be assessed by an ingestible pill thermometer and scrotal temperature will be assessed by skin sensor placed in the scrotum of male participants, to assess the thermoregulation of the scrotum during firefighting exercises. Time series of core body temperature and scrotal skin temperature will be analysed for eventual thermoregulation disruption.
Time frame: Baseline day, during the day of firefighting without fire, during the day of firefighting under wood fire and during the day of firefighting under gas fire.
Changes in levels of circulating micro RNA
Circulating micro RNA candidates will be measured by RNA extraction from serum samples, reverse transcribed into complementary DNA (cDNA) and analysed with quantitative polymerase chain reaction (qPCR).
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in urinary potency of AhR activation
The aryl hydrocarbon receptor (AhR) activation will be assessed in vitro using urine samples on the PAH CALUX (Chemical Activated LUciferase gene eXpression bioassay) reporter assay. The smoke and soot exposures are complex mixtures of compounds with potential toxic effect. Routine measurements of PAHs are usually quantified for a target list of 16 common soot elements and even less chemical species for urinary metabolites, but many other compounds are present in both soot and metabolites mixtures. The toxicity of PAHs is primarily caused through the binding to AhR, and induction of AhR related genes and subsequent toxic pathways. The outcome will be measured in the form of benzo\[a\]pyrene equivalence.
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in potency of AhR activation from skin deposits
The aryl hydrocarbon receptor (AhR) activation will be assessed in vitro using wipe samples on the PAH CALUX (Chemical Activated LUciferase gene eXpression bioassay) reporter assay. The smoke and soot exposures are complex mixtures of compounds with potential toxic effect. Routine measurements of PAHs are usually quantified for a target list of 16 common soot elements, but many other compounds are present in soot mixtures. The toxicity of PAHs is primarily caused through the binding to AhR, and induction of AhR related genes and subsequent toxic pathways. The outcome will be measured in the form of benzo\[a\]pyrene equivalence.
Time frame: Baseline, before firefighting without fire, immediately after firefighting without fire, before firefighting under wood fire, immediately after firefighting under wood fire, before firefighting under gas fire, immediately after firefighting under gas
Changes in levels of follicle-stimulating hormone in serum
Follicle-stimulating hormone (FSH) will be measured in serum samples
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in levels of serum inhibin B
Inhibin B hormone will be measured in serum samples
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in urinary levels of PAH metabolites excretion
The internal dose of polycyclic aromatic hydrocarbons (PAHs), that would have the contribution from different exposure routes, will be assessed in first morning urine samples and measured for 7 isomer hydroxyl-PAH compounds and 5 nitro-PAH compounds, measured by high-performance liquid chromatography (HPLC)
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in levels of PAHs in skin wipes from the neck
Skin wipes will be sampled to determine the PAH composition of deposited soot on the neck area. The wipes will be analysed for the 16 US Environmental Protection Agency priority list of PAH compounds by HPLC.
Time frame: Baseline, before firefighting without fire, immediately after firefighting without fire, before firefighting under wood fire, immediately after firefighting under wood fire, before firefighting under gas fire, immediately after firefighting under gas
Changes in FEV1 spirometric measurements
Lung function will be measured by spirometry using the Spirometer device EasyOne Air. Forced Expiratory Volume at 1 second (FEV1).
Time frame: Baseline, immediately after firefighting without fire, immediately after firefighting under wood fire and immediately after firefighting under gas fire
Changes in FVC spirometric measurements
Lung function will be measured by spirometry using the Spirometer device EasyOne Air. Forced Vital capacity (FVC).
Time frame: Baseline, immediately after firefighting without fire, immediately after firefighting under wood fire and immediately after firefighting under gas fire
Changes in PEF spirometric measurements
Lung function will be measured by spirometry using the Spirometer device EasyOne Air. Peak Expiratory Flow (PEF).
Time frame: Baseline, immediately after firefighting without fire, immediately after firefighting under wood fire and immediately after firefighting under gas fire
Changes in FEV1/FVC ratio from spirometric measurements
Lung function will be measured by spirometry using the Spirometer device EasyOne Air. Forced Expiratory Volume at 1 second (FEV1) and Forced Vital Capacity (FVC) ratio is calculated from device output.
Time frame: Baseline, immediately after firefighting without fire, immediately after firefighting under wood fire and immediately after firefighting under gas fire
Changes in blood troponin levels
Cardiac troponin levels using ELISA immunoassays will be assessed in serum samples.
Time frame: Baseline, before firefighting without fire, day after firefighting without fire, before firefighting under wood fire, day after firefighting under wood fire, before firefighting under gas fire, day after firefighting under gas fire
Changes in work load measured by muscle activity
Muscle activity will be assessed to control for body workload through electromyography (EMG) using the portable device Nexus10. Bipolar surface EMG electrodes are applied to the skin over the muscles in 3 relevant body regions (shoulder, leg and back). The signals are collected with a data logger and reported as work load during a working day.
Time frame: Baseline day, firefighting without fire day, firefighting under wood fire day and firefighting under gas fire day
Plan to share: No — Supportive information and fully anonymized information will be shared and whenever possible (in supplementary material) published along with the results, but following European Union General Data Protection Regulation (GDPR) and Danish rules, no non or pseudo anonymized data might be shared.
Ran from Mar 2023 to primary completion in Jul 2024, 15 months.
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National Research Centre for the Working Environment, Denmark