Scottish Firefighters Occupational Cancer and Disease Mortality Rates: 2000-2020

Abstract Background Increased mortality from cancers and other diseases has been reported in USA, Canadian, and Nordic firefighters. However, UK firefighters are understudied. Aims To determine whether UK firefighters suffer increased mortality from cancers and other diseases when compared with the general population. Methods Mortality from cancer and other diseases in Scottish male firefighters between 2000 and 2020 was compared with the general Scottish male population and expressed as standardized mortality ratios (SMRs) (with 95% confidence intervals, CI). Results Significant overall excess cancer mortality was found for Scottish firefighters compared with the general population (SMR 1.61, CI 1.42-1.81). Scottish firefighters were nearly three times more likely to die of malignant neoplasms (unspecified sites) (SMR 2.71, CI 1.71-4.00). Excess cancer mortality was also found for several site-specific cancers, including prostate (SMR 3.80, CI 2.56-5.29), myeloid leukaemia (SMR 3.17, CI 1.44-5.58), oesophagus (SMR 2.42, CI 1.69-3.29) and urinary system (kidney and bladder) (SMR 1.94, CI 1.16-2.91). Mortality from neoplasms of unknown behaviour was over six times greater in Scottish firefighters (SMR 6.37, CI 2.29-12.49). Additionally, significantly higher mortality was found for: acute ischaemic heart diseases (SMR 5.27, CI 1.90-10.33), stroke (SMR 2.69, CI 1.46-4.28), interstitial pulmonary diseases (SMR 3.04, CI 1.45-5.22), renal failure (SMR 3.28, CI 1.18-6.44) and musculoskeletal system diseases (SMR 5.64, CI 1.06-13.83). Conclusions UK firefighters suffer significant excess mortality from cancer and other diseases when compared with the general population. Preventative health monitoring and presumptive legislation are urgently required to protect UK firefighters’ health.


Introduction
Recently, the World Health Organisation's (WHO) International Agency for Research on Cancer (IARC), re-classified occupational exposure as a firefighter as 'carcinogenic to humans' (Group 1) [1]. The IARC review considers the growing number of studies worldwide which indicate elevated incidences of cancers and other diseases in firefighters [3].
It is increasingly recognized that exposure to fire effluent (through inhalation, ingestion or dermal absorption) is likely to be a significant risk factor for such cancers and diseases [4]. Fire effluent comprises a cocktail of toxic, irritant and carcinogenic species which vary depending on the specific materials burning and the fire conditions at the incident [5]. Asphyxiants (carbon monoxide or hydrogen cyanide) and irritant fire gases (hydrogen halides, nitrogen oxides, aldehydes, etc.) are associated with acute health effects. However, fire effluent also contains a range of chronic toxicants with genotoxic and carcinogenic properties. Regardless of the fuel, carcinogens such as benzene, polycyclic aromatic hydrocarbons (PAHs) and toluene are released in almost all fires. Polychloro-and polybromo-dibenzodioxins and dibenzofurans, and respiratory sensitizers such as isocyanates, and heavy metals (lead, cadmium, etc.) have also been identified in fire effluents and associated with chronic health conditions such as cancer [6].
In the USA, Canada and Australia, the link between exposure to fire effluent and increased incidence of cancers in firefighters is officially recognized in some states/provinces, with presumptive legislation protecting firefighters' right to medical support and/or workplace compensation should they develop cancer because of their careers.
However, little such support is in place for UK firefighters. The UK's Industrial Injuries Advisory Council (IIAC) failed to recognize cancer (except mesothelioma) as an occupational risk for UK firefighters. The lack of sufficient evidence (due to a lack of studies on UK firefighters) was cited as one of the key reasons for this decision.
To date, there have been only two studies investigating cancer incidence and mortality rates in UK firefighters specifically [7,8]. While limited, these studies hint at cancer becoming a growing concern for UK firefighters over time, whereby initial investigation of the topic over the 1965-1993 period found reduced cancer incidence/mortality in firefighters [8], and subsequent study over the 1984-2005 period found significantly higher mortality rates for kidney cancer [7].
In this manuscript, cancer and disease mortality among Scottish male firefighters over a more recent period (between 2000 and 2020) was compared with the general Scottish male population and calculated as standardized mortality ratios (SMRs) (with 95% confidence intervals, CI).

Methods
Mortality records for the period 2000-2020 were obtained from the National Records of Scotland (NRS) for those with a firefighting-relevant occupation, through a freedom of information request. Records were requested for firefighters between the ages of 30-74, accounting for the long latent period of many cancers [9]. A total of 672 fully anonymized records were returned from this request, accounting for both serving and retired firefighters. Ethical review by the University of Central Lancashire Ethics Committee was not required as all data was publicly accessible and fully anonymized.
Analysis included only whole-time operational and retained firefighters. Due to their small sample size, records concerning female firefighters (n = 11) were excluded from the analysis. Records concerning supporting staff (n = 96), and those employed by other (private) sectors (aviation, railway, healthcare, etc., n = 423) were also excluded, as it was not possible to confirm that these roles involved active firefighting. Any deaths which were not due to cancer or disease (e.g. external factors such as suicide, drowning, etc.) were also excluded (n = 48).
A total of 623 mortality records were included in the analyses (n = 285 for cancer mortality and n = 338 for other diseases).
The total population of male Scottish firefighters between the ages of 30-74 was estimated by combining figures for employed and retired firefighters over the 2000-2020 period.
Firefighter establishment figures for the years 2000-2020 were obtained from annual publications by the Scottish Fire and Rescue Service, and annual publications by Her Majesty's Inspectorate of Constabulary and Fire and Rescue Services [10]. Figures for retired firefighters were obtained from the Scottish Public Pensions Agency, through a freedom of information request.
General Scottish population and mortality data for males between the ages of 30-74 were sourced using the NRS online access tool [11], and through Public Health Scotland (part of the National Health Service (NHS) National Services Scotland cancer registry data) and used to calculate the expected number of firefighter deaths due to cancer/disease in each age group for the 2000-2020 period. Standardized mortality ratios (adjusted for age and calendar year) were then calculated using the actual number of firefighter deaths as obtained above [12]. Ninety-five percent confidence intervals were calculated using methods described by Ulm [13]. Figure 1 shows a histogram presenting an age breakdown from 2000 to 2020 for the general population and firefighters. The modal age category for firefighters was 45-49 years (approximately 24%) while for the general population it was distributed across 35-54 years (approximately 12%). Table 1 presents the standardized firefighter mortality ratios and 95% confidence intervals (CI) for cancers and other diseases among male Scottish firefighters compared with the general population of males in Scotland.

Results
Overall, malignant neoplasms (cancer) mortality among male Scottish firefighters was significantly higher compared with the male general population (SMR 1.61, CI 1.2-1.81), as summarized in Table 1. Statistically significant SMRs, greater than 2.0, were observed for cancers of the prostate (SMR 3.80, CI 2.56-5.29), myeloid leukaemia (SMR 3.17, CI 1.44-5.58) and oesophagus (SMR 2.42, CI 1.69-3.29). SMRs for cancers without specification of the site were also greater than 2.0 (SMR 2.73, CI 1.71-4.00), as were SMRs for neoplasms of unknown behaviour (SMR 3.17, CI 1.44-5.58). The SMR for malignant neoplasms of the urinary system (such as kidney and bladder) was also close to 2.0 when compared with the general population (SMR 1.94, CI 1.16-2.91).

Key learning points
What is already known about this subject: • The International Agency for Research on Cancer (WHO), recently classified firefighters' occupational exposure as carcinogenic [1]. • In the USA, Canada, and Australia, cancer is a prescribed occupational disease in firefighters, whereby presumptive legislation protects firefighters' right to financial and medical support should they develop cancer because of their career. • Recently, the UK's Industrial Injuries Advisory Council (IIAC) failed to recognize cancer as a prescribed disease in firefighters-citing a lack of available UK-specific evidence [2].

What this study adds:
• This study finds significant excess cancer and other disease mortality amongst male Scottish firefighters compared to the general male population.
What impact this has on policy/practice: • Scottish firefighters were found to be at least twice as likely to die from several cancers/diseases compared with the general male population-surpassing the Industrial Injuries Advisory Council (IIAC)'s relative risk threshold for prescription of an occupational disease. • These findings warrant urgent review of IIAC's decision regarding prescription of cancer as an occupational disease in UK firefighters, and calls for greater legal support for UK firefighters suffering cancer because of their careers. • These findings also support calls for regular preventative health monitoring among UK firefighters-as recently debated in the Northern Irish Assembly, where a motion was passed calling for annual cancer screening for serving firefighters.
(kidney and liver, SMR 3.28, CI 1.18-6.44) and possibly diseases of the musculoskeletal system (SMR 5.64, CI 1.06-13.83)-although a relatively small number of cases was identified for the latter (Table 1).

Discussion
Male Scottish firefighters were found to have significant excess mortality for a range of cancers and diseases when compared with the male general population. The implications of these findings are discussed below. Figure 2 presents the total number of disease and cancer deaths from 2000 to 2020, for the general population and firefighters. An overall downward trend in the number of cancer deaths in the general population over time reflects the introduction, and increasing availability of, life-saving measures such as early diagnostics and effective treatment, as outlined in the UK NHS's Long-Term Plan [14]. However, this downward trend is not observed in firefighters, Figure 2B, who rather display a concerning upward trend in number of cancer deaths over time. There may be several plausible explanations for this observation. As demonstrated in Figure 3, Scottish firefighters appear to have higher cancer death rates at younger age brackets (e.g. see 55-59, Figure 3) when compared to the general population (e.g. see 70-74, Figure 3). These firefighters may be too young to be offered national NHS cancer screening programmes, which are typically targeted at older demographics-preventing early diagnosis and treatment. Additionally, firefighters may be more susceptible to specific cancers which are less common in the general population (Table 1) and are thus not targeted by national screening programmes-again delaying diagnosis and treatment. Finally, the increasing domination of synthetic materials (which produce a more toxic fire effluent) in modern times may in part contribute to the apparent increase in firefighter cancer deaths over time.
The excess cancer mortality observed in Scottish firefighters for several site-specific cancers suggests a significant contribution from several exposure pathways and/or fire toxins.
Excess mortality for cancers of the oesophagus (SMR = 2.42, CI 1.69-3.29) and digestive organs in Scottish firefighters hint at a potentially significant contribution from the ingestion exposure pathway. Ingestion may occur when firefighters swallow mucus in which fire effluent has become trapped or eat with contaminated hands. Over 85% of recently surveyed UK firefighters reported noticing soot in their nose and throat after attending a fire, with those noticing soot in the nose/throat for more than a day being twice as likely to report a cancer diagnosis than those who did not notice soot in their nose/throat after incidents [15]. Similarly, just over 85% and 56% of recently surveyed firefighters reported eating while wearing PPE or with sooty hands respectively (with those eating while wearing PPE being 1.8 times more likely to report a cancer diagnosis than those who do not engage in this practice [15]). Occupational exposure to soot has previously been associated with an increased incidence of oesophageal cancers in the UK [16].
Significant excess mortality from myeloid leukaemia (SMR 3.17, CI 1.44-5.58) and myelodysplastic syndrome (sometimes leading to acute myeloid leukaemia) (SMR 5.56, CI 1.05-13.63) was also identified in Scottish firefighters. These conditions have been found to be associated with exposure to fire effluents such as PAHs, 1,3-butadiene, ethylene oxide and formaldehyde [17]. Myeloid leukaemia has been found to be strongly associated with exposure to benzene; released in almost all fire scenarios [18,19]. A recent exposure study noted increased benzene concentrations in firefighters' exhaled breath following firefighting activities, despite the use of breathing apparatussuggesting a significant contribution of the dermal absorption exposure pathway [20].
Prostate cancer, for which Scottish firefighters had significant excess mortality (SMR 3.80 (2.56,5.29)), has also been associated with exposure to chemicals present in fire effluent including benzene and styrene [21] Figure 2A compares the total number of deaths due to noncancer diseases between 2000 and 2020 for Scottish firefighters and the general population. The 'flat-line' in disease mortality over time suggests a significant contribution of other firefighting risk factors, which are more inherently and consistently associated with the firefighting role, i.e. frequent extreme physical exertion, heat stress, dehydration. etc. [22].
Heart diseases have been studied in firefighting populations across the globe [23]. Scottish firefighters were found to   I10-12, I21, I24-27, I33, I35, I42, I48, I51, I60-64, I67, I69, I71, I73, I80  171  . Exposure to fire effluents such as carbon monoxide and hydrogen cyanide can reduce the amount of oxygen taken up by the lungs, forcing the heart to work harder to supply the greater volume of oxygen required during periods of physical stress while engaged in active firefighting [9]. Scottish firefighters were also found to have significant excess mortality for interstitial pulmonary diseases (SMR = 3.04, CI 1.45-5.22). Interstitial pulmonary diseases are characterised by inflammation or scarring of lung tissue and include asbestosis, pulmonary fibrosis and sarcoidosis. Interstitial pulmonary diseases have been identified in firefighters at rates up to four times that of the general population [24]. Inhalation exposure to asbestos, silica and inorganic dust is thought to contribute to firefighters' increased risk. Nitrogen dioxide, sulphur dioxide, carbon monoxide, particulate matter and metals have also been strongly associated with adverse respiratory outcomes [25]. Additionally, diisocyanatos (found in polyurethane foams) have been found to induce hypersensitivity pneumonitis that may progress to pulmonary fibrosis (a subtype of interstitial pulmonary disease).
Excess mortality due to renal failure (SMR 3.28, CI 1.18-6.44) was also found among Scottish firefighters. It is worth noting that cancer mortality due to cancers of the urinary system (i.e. combined kidney and bladder cancers) was also elevated in Scottish firefighters. Dehydration is a significant risk factor for firefighters which can cause kidney damage. Additionally, increased blood flow, sweating rates and body temperature, together with the body's reduced water content, may increase dermal intake of fire effluents. Thus, a combination of frequent dehydration, and chronic exposure to fire effluents, may act synergistically to damage the kidneys [26,27].    The findings discussed above indicate an urgent need to better support firefighters' health. Support is required in three key areas: prevention, monitoring and remediation/ compensation.
Prevention requires identifying underlying causes of excess cancer/disease and implementing measures which protect firefighters from these causes. Work is already underway to better protect firefighters from exposure to toxic fire effluents, e.g. through standardising decontamination procedures [28]. However, there is currently no formal preventative cancer or other disease monitoring programme in place for UK firefighters [15].
Early detection is acknowledged as one of the best indicators of cancer survival. Given the younger ages at which firefighters appear to be developing and dying of cancer, a dedicated health monitoring programme is urgently required. This need was recently acknowledged during a debate in the Northern Irish Assembly, where a motion was passed calling for annual cancer screening for serving firefighters [29].
Monitoring describes the process of continual data collection regarding firefighters' exposures and health. The UK Firefighter Cancer and Disease Registry goes some way to serving this purpose [30], acting as a living repository of health and exposure data. However, there is much scope for further monitoring UK firefighters' health and exposure. Critically, monitoring should ensure that preventative health monitoring is conducted on a regular, continual basis-considering rapid advances in cancer screening technology and treatment.
Finally, for many firefighters, the immediate implementation of these measures may already be too late due to the long latent period of cancer, and the significant impact of chronic low-dose exposures. Thus, remedial measures are required to ensure that firefighters who develop cancer in service of their role have access to necessary financial and medical support. Such measures are established in countries such as Canada, the USA and Australia, but not in the UK or Europe.
Recently, the UK's Industrial Injuries Advisory Council failed to recognize cancer as a prescribed disease for firefighters in the UK, citing insufficient evidence. In addition, it considers a relative risk threshold for prescription more than double that of the general population . Given the findings presented in this manuscript, we urge an immediate review of this decision.
While the comprehensiveness of the studied firefighter population and its inclusion of retired members are strengths, a weakness of this work is that data were accessed from Scotland only, not the whole UK. Scotland has its own harmonized and independent recording system of statistics and pensions when compared with the rest of the UK (where compiling) such data is more difficult and time-consuming.
The prime recognized limitation of this study is the fact that extracts of entry in a Register of Deaths list just one occupation-the last one held prior to death. Given that, for many years, firefighters could retire between the ages of 55 and 60 (or earlier if they were discharged on the grounds of ill health), they could subsequently obtain further employment. This may result in an underestimation of firefighter deaths and SMRs (particularly for rare cancers).
The association of occupational exposure as a firefighter and deaths due to cancer/disease would also benefit from collecting information on firefighters' length of employment. Together with information on historical or/and post-retirement occupation, this would allow more accurate characterization of risk.