Sudden Cardiac Death Among Firefighters ≤45 Years of Age in the United States

Sudden cardiac death (SCD) is the leading cause of death in firefighters. Although on-duty SCD usually occurs in older victims almost exclusively because of coronary heart disease, no studies have examined causation across the career span. In the present retrospective case-control study, cases of SCD in young (aged ≤45 years) firefighters from the National Institute for Occupational Safety and Health fatality investigations (n = 87) were compared with 2 age- and gender-matched control groups: occupationally active firefighters (n = 915) and noncardiac traumatic firefighter fatalities (n = 56). Of the SCD cases, 63% were obese and 67% had a coronary heart disease–related cause of death. The SCD victims had much heavier hearts (522 ± 102 g) than noncardiac fatality controls (400 ± 91 g, p 450 g) was found in 66% of the SCD victims and conveyed a fivefold increase (95% confidence interval CI 1.93 to 12.4) in SCD risk. Furthermore, hypertension, including cases with left ventricular hypertrophy, increased SCD risk by 12-fold (95% CI 6.23 to 22.3) after multivariate adjustment. A history of cardiovascular disease and smoking were also independently associated with elevated SCD risk (odds ratio 6.89, 95% CI 2.87 to 16.5; and odds ratio 3.53, 95% CI 1.87 to 6.65, respectively). In conclusion, SCD in young firefighters is primarily related to preventable lifestyle factors. Obesity entry standards, smoking bans, and improved screening and/or wellness program are potential strategies to reduce SCD in younger firefighters. Sudden cardiac death (SCD) is the leading cause of death in firefighters. Although on-duty SCD usually occurs in older victims almost exclusively because of coronary heart disease, no studies have examined causation across the career span. In the present retrospective case-control study, cases of SCD in young (aged ≤45 years) firefighters from the National Institute for Occupational Safety and Health fatality investigations (n = 87) were compared with 2 age- and gender-matched control groups: occupationally active firefighters (n = 915) and noncardiac traumatic firefighter fatalities (n = 56). Of the SCD cases, 63% were obese and 67% had a coronary heart disease–related cause of death. The SCD victims had much heavier hearts (522 ± 102 g) than noncardiac fatality controls (400 ± 91 g, p 450 g) was found in 66% of the SCD victims and conveyed a fivefold increase (95% confidence interval CI 1.93 to 12.4) in SCD risk. Furthermore, hypertension, including cases with left ventricular hypertrophy, increased SCD risk by 12-fold (95% CI 6.23 to 22.3) after multivariate adjustment. A history of cardiovascular disease and smoking were also independently associated with elevated SCD risk (odds ratio 6.89, 95% CI 2.87 to 16.5; and odds ratio 3.53, 95% CI 1.87 to 6.65, respectively). In conclusion, SCD in young firefighters is primarily related to preventable lifestyle factors. Obesity entry standards, smoking bans, and improved screening and/or wellness program are potential strategies to reduce SCD in younger firefighters. The leading mode of duty-related death among US firefighters is sudden cardiac death (SCD), which accounts for about 50% of on-duty firefighting fatalities.1Soteriades E.S. Smith D.L. Tsismenakis A.J. Baur D.M. Kales S.N. Cardiovascular disease in US firefighters: a systematic review.Cardiol Rev. 2011; 19: 202-215Crossref PubMed Scopus (297) Google Scholar, 2Fahy R.F. LeBlanc P. Molis J.L. Firefighter Fatalities in the United States–2011. National Fire Protection Association, Quincy, MA2012: 1-36Google Scholar, 3Smith D.L. Barr D.A. Kales S.N. Extreme sacrifice: sudden cardiac death in the US Fire Service.Extrem Physiol Med. 2013; 2: 6Crossref PubMed Scopus (102) Google Scholar, 4Fahy R.F. U.S. Firefighter Fatalities Due to Sudden Cardiac Death, 1995–2004. National Fire Protection Association, Quincy, MA2005: 1-11Google Scholar About 90% of these SCD cases will be attributable to coronary heart disease (CHD) and usually occur in firefighters aged >45 years.4Fahy R.F. U.S. Firefighter Fatalities Due to Sudden Cardiac Death, 1995–2004. National Fire Protection Association, Quincy, MA2005: 1-11Google Scholar, 5Kales S.N. Soteriades E.S. Christoudias S.G. Christiani D.C. Firefighters and on-duty deaths from coronary heart disease: a case control study.Environ Health. 2003; 2: 14Crossref PubMed Google Scholar, 6Holder J.D. Stallings L.A. Peeples L. Burress J.W. Kales S.N. Firefighter heart presumption retirements in Massachusetts 1997–2004.J Occup Environ Med. 2006; 48: 1047-1053Crossref PubMed Scopus (42) Google Scholar, 7Kales S.N. Soteriades E.S. Christophi C.A. Christiani D.C. Emergency duties and deaths from heart disease among firefighters in the United States.N Engl J Med. 2007; 356: 1207-1215Crossref PubMed Scopus (414) Google Scholar In addition, emerging evidence has suggested that obesity and left ventricular (LV) hypertrophy and/or cardiomegaly are present in a large proportion of all those with SCD (with and without CHD) in firefighters8Geibe J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar and the general population.9Tavora F. Zhang Y. Zhang M. Li L. Ripple M. Fowler D. Burke A. Cardiomegaly is a common arrhythmogenic substrate in adult sudden cardiac deaths, and is associated with obesity.Pathology. 2012; 44: 187-191Crossref PubMed Scopus (42) Google Scholar Although SCD causation in younger subjects, such as athletes, is usually due to non-CHD structural pathologic features,10Maron B.J. Sudden death in young athletes.N Engl J Med. 2003; 349: 1064-1075Crossref PubMed Scopus (1170) Google Scholar, 11Braunwald E. Zipes D.P. Libby P. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. Elsevier Saunders, Philadelphia2001: 876Google Scholar little is known about SCD in young firefighters. We conducted a case-control study of SCD among firefighters aged ≤45 years to examine the associated cardiovascular disease (CVD) risk factors and underlying pathologic features. Our aims were to (1) describe the specific pathologic-anatomic causes of on-duty SCD in these cases, (2) compare the prevalence and severity of CVD risk factors in SCD fatalities with those in healthy, occupationally active firefighter controls, and (3) compare the cardiac findings from the SCD cases at autopsy with those of firefighters who died of on-duty noncardiac causes. We conducted a retrospective case-control study that serially reviewed and selected as cases all SCD fatalities (aged ≤45 years) from 1996 to 2012 investigated by the National Institute for Occupational Safety and Health (NIOSH).12NIOSHFire Fighter Fatality Investigation Reports. National Institute for Occupational Safety and Health, Atlanta2012http://www.cdc.gov/niosh/fire/Google Scholar Two other firefighter groups were chosen as controls: (1) age-matched, career firefighters examined from 2007 to 200913Baur D.M. Leiba A. Christophi C.A. Kales S.N. Low fitness is associated with exercise abnormalities among asymptomatic firefighters.Occup Med (Lond). 2012; 62: 566-569Crossref PubMed Scopus (25) Google Scholar and (2) age-matched, noncardiac, traumatic fatalities (2004 to 2010) with autopsy reports available. NIOSH conducts independent investigations of firefighter line-of-duty deaths, and the completed fatality reports are publicly available for download from NIOSH's Firefighter Fatality Investigation and Prevention Program website.12NIOSHFire Fighter Fatality Investigation Reports. National Institute for Occupational Safety and Health, Atlanta2012http://www.cdc.gov/niosh/fire/Google Scholar Two physician investigators (J.Y. and D.T.) examined in detail all fatality reports published online from January 1996 to December 2012 to determine whether each case met our inclusion criteria as listed in the following paragraph. A third physician investigator (A.F.) then reviewed the NIOSH database and previously selected cases again, with final decisions on inclusion resolved by the senior investigator (S.N.K.). SCD case data were extracted using a standardized electronic template5Kales S.N. Soteriades E.S. Christoudias S.G. Christiani D.C. Firefighters and on-duty deaths from coronary heart disease: a case control study.Environ Health. 2003; 2: 14Crossref PubMed Google Scholar, 8Geibe J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar by 2 of us (D.T. and J.Y.) independently and then were verified for completeness and accuracy (by J.Y.). Any disagreements among the investigators on data extraction were resolved by the senior physician investigator (S.N.K.). The inclusion criteria for the NIOSH SCD fatality cases were (1) NIOSH investigated cases published on the website from January 1996 to December 2012, (2) firefighters who experienced SCD and died within 24 hours of their last fire service duty or experienced a sudden cardiac event within 24 hours of their last duty and the event was associated with loss of consciousness within 1 hour of onset, and, subsequently, the firefighter never regained consciousness before biologic death, (3) age ≤45 years, and (4) autopsy report or sufficient medical findings available to determine the underlying cause of death. An existing database previously assembled from career fire departments was reviewed for occupationally active control firefighters. The cohort's cardiovascular and health status were comprehensively characterized by baseline fire department medical examinations.13Baur D.M. Leiba A. Christophi C.A. Kales S.N. Low fitness is associated with exercise abnormalities among asymptomatic firefighters.Occup Med (Lond). 2012; 62: 566-569Crossref PubMed Scopus (25) Google Scholar, 14Baur D.M. Christophi C.A. Kales S.N. Metabolic syndrome is inversely related to cardiorespiratory fitness in male career firefighters.J Strength Cond Res. 2012; 26: 2331-2337Crossref PubMed Scopus (59) Google Scholar The inclusion criteria for the occupationally active firefighter controls were (1) age ≤45 years, and (2) no medical restrictions or physical limitations on duty. Potential age-matched, noncardiac traumatic fatalities (deaths due to blunt trauma, burns, or asphyxiation) were identified for 2004 to 2010 from a firefighter autopsy research data bank maintained by 1 of us (D.S.) and the National Fallen Firefighters Foundation. The inclusion criteria for the National Fallen Firefighters Foundation noncardiac traumatic controls were (1) age ≤45 years, (2) death while on duty, and (3) cause of death determined by autopsy to be due to blunt trauma, burns, or asphyxiation and not related to any cardiovascular pathologic entity. Among the occupationally active controls, firefighters were considered active smokers if they self-reported smoking within the previous 12 months. Diabetes mellitus was defined using the Framingham criteria (random blood glucose ≥150 mg/dl, previous diagnosis of diabetes, and/or requiring diabetes mellitus medications).5Kales S.N. Soteriades E.S. Christoudias S.G. Christiani D.C. Firefighters and on-duty deaths from coronary heart disease: a case control study.Environ Health. 2003; 2: 14Crossref PubMed Google Scholar, 8Geibe J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar Hypertension was considered present if firefighters had a systolic blood pressure of ≥140 mm Hg and/or diastolic blood pressure of ≥90 mm Hg at rest, a previous hypertension diagnosis, and/or required hypertension medication. Firefighters with a total cholesterol level of ≥200 mg/dl, low-density lipoprotein of ≥160 mg/dl, a previous diagnosis of hyperlipidemia, and/or requiring lipid-lowering medications were considered to have dyslipidemia. In the NIOSH SCD cases, the determinations were according to the same criteria or a description of the risk factors as presented by the NIOSH investigators anywhere in the case report. We also considered a second definition of hypertension that included those with hypertension as defined plus those with LV hypertrophy found on autopsy.8Geibe J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar Any firefighter was considered to have a history of CHD or CHD equivalent if the NIOSH report or medical record reported previous myocardial infarction, angioplasty, stent placement, or a clinical diagnosis of CHD on the basis of an abnormal calcium score or exercise tolerance test findings. A history of valvular disease was considered present if a previous diagnosis of valvular abnormalities and/or disease or appropriate autopsy findings of valvular disease were present. A “history of chest pain or shortness of breath” was considered present if the firefighter had had episodes of chest pain and/or shortness of breath documented without a CHD diagnosis. We conservatively coded the CVD risk factors in the SCD cases as negative when these were undeterminable or ambiguous from the investigation report. The use of de-identified data from the occupationally active firefighter controls was previously approved by the institutional review board of Harvard School of Public Health and local institutional review boards, as appropriate. The investigations and autopsy reports from NIOSH and the National Fallen Firefighters Foundation were exempt from institutional review board review (deceased, nonliving of Health and Protection of US of Health and Scholar were using and were compared using test and using of risk factors with SCD were characterized by odds and associated 95% confidence to be in the multivariate were selected a p were considered and all were A total of SCD fatality cases, occupationally active controls, and deaths met the inclusion The SCD cases by age are listed in with and/or cardiomegaly in the of CHD were associated with or 67% of SCD cases had CHD as a 1 and of sudden cardiac death (SCD) cases aged ≤45 years from the National Institute for Occupational Safety and Health (n = (n = (n = ± ± ± ± (n = ± (n = ± (n = status findings CHD LV hypertrophy or hypertension heart CHD because of (2) disease heart disease other than coronary (1) and other without structural (1) Cardiac (2) cardiovascular (2) of SCD not of SCD not be because of of autopsy and previous medical weight ± (n = ± (n = ± 102 (n = weight >450 are presented as ± or = = of SCD not be because of of autopsy and previous medical in a are presented as ± or = = The CVD risk prevalence the NIOSH SCD cases and occupationally active firefighter controls is presented in The odds for and hypertension were all for an with SCD after multivariate adjustment. A history of CHD or valvular disease before death was associated with a increase in the risk of after multivariate (95% confidence interval 2.87 to of cardiovascular disease (CVD) risk factors sudden cardiac death (SCD) cases aged ≤45 years from National Institute for Occupational Safety and Health investigations with occupationally active firefighter (n = (n = by diabetes hypertension, and to cases and controls with to cases and controls with by diabetes hypertension and ± ± was smoking within previous 12 Diabetes evidence of diabetes mellitus in controls: blood glucose ≥150 mg/dl, previous diabetes mellitus diagnosis, and/or blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm previous hypertension diagnosis, and/or Hypertension all cases of hypertension defined in previous plus those with findings of LV hypertrophy on of cholesterol ≥200 or low-density lipoprotein ≥160 previous diagnosis of hyperlipidemia, and/or of CVD CHD or valvular CHD previous myocardial infarction, angioplasty, stent placement, or clinical diagnosis of CHD because of abnormal calcium score or exercise tolerance test valvular disease: previous diagnosis of valvular abnormalities or disease or of appropriate autopsy findings on or pain or shortness of of chest pain or shortness of breath documented without a CHD are presented as ± or = confidence = hypertension 2 = second definition of = odds = by diabetes hypertension, and to cases and controls with by diabetes hypertension and was smoking within previous 12 evidence of diabetes mellitus in controls: blood glucose ≥150 mg/dl, previous diabetes mellitus diagnosis, and/or blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm previous hypertension diagnosis, and/or all cases of hypertension defined in previous plus those with findings of LV hypertrophy on of cholesterol ≥200 or low-density lipoprotein ≥160 previous diagnosis of hyperlipidemia, and/or CHD previous myocardial infarction, angioplasty, stent placement, or clinical diagnosis of CHD because of abnormal calcium score or exercise tolerance test valvular disease: previous diagnosis of valvular abnormalities or disease or of appropriate autopsy of chest pain or shortness of breath documented without a CHD diagnosis. in a are presented as ± or CI = confidence = hypertension 2 = second definition of = odds = from the SCD cases and noncardiac controls are listed in Our SCD cases had hearts g) compared with the controls 450 g) after multivariate (95% confidence interval 1.93 to in groups cardiomegaly primarily in obese of cases and 67% of controls with an heart were sudden cardiac death (SCD) cases aged ≤45 years from National Institute for Occupational Safety and Health investigations and traumatic fatality SCD (n = (n = ± ± from that included and heart to cases and controls with from that included and heart to cases and controls with from that included and heart to cases and controls with from that included and heart to cases and controls with weight ± ± from that included and heart to cases and controls with from that included and heart to cases and controls with weight from that included and heart to cases and controls with from that included and heart to cases and controls with are presented as ± or = confidence = odds = from that included and heart to cases and controls with from that included and heart to cases and controls with in a are presented as ± or CI = confidence = odds = The from the present study the that on-duty SCD in younger US those aged years, is primarily related to preventable lifestyle which in and LV hypertrophy and/or Our study also identified risk factors for with SCD were to be and smokers and to have a history of CVD than were active Furthermore, when the SCD autopsy were compared with those from other firefighters who died of noncardiac the SCD cases were had heart and had an increased risk of cardiomegaly (heart weight >450 Two of the SCD cases had a heart weight >450 and In with data from the general F. Zhang Y. Zhang M. Li L. Ripple M. Fowler D. Burke A. Cardiomegaly is a common arrhythmogenic substrate in adult sudden cardiac deaths, and is associated with obesity.Pathology. 2012; 44: 187-191Crossref PubMed Scopus (42) Google Scholar found that the common underlying pathologic for SCD in younger firefighters was with cardiomegaly SCD cases were due to CHD or of cardiomegaly for cardiomegaly and obesity were also with an study of SCD in the fire service that was to CHD deaths, in which the age of those was years and of the were >45 years J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar In our present study, 63% of those with SCD were obese compared with of the active firefighter a increased risk of SCD after for of the SCD cases had or obesity compared with of our occupationally active control firefighters. Our be by with the of risk hypertension and which increase the risk of CHD and as as A.J. Christophi C.A. Burress J.W. Kinney A.M. M. Kales S.N. The obesity and PubMed Scopus Google Scholar, D. Kales A. and in obese Med. PubMed Scopus Google Scholar LV hypertrophy was of in with previous D.L. Barr D.A. Kales S.N. Extreme sacrifice: sudden cardiac death in the US Fire Service.Extrem Physiol Med. 2013; 2: 6Crossref PubMed Scopus (102) Google Scholar, D. of determined left ventricular in the Framingham Heart Engl J Med. PubMed Scopus Google Scholar, D. ventricular hypertrophy by and in the Framingham Med. PubMed Scopus Google Scholar, D.A. J. Burke The of left ventricular and to cardiovascular the of Cardiol. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar In previous investigations of CHD fatalities among LV hypertrophy was found in to of D.L. Barr D.A. Kales S.N. Extreme sacrifice: sudden cardiac death in the US Fire Service.Extrem Physiol Med. 2013; 2: 6Crossref PubMed Scopus (102) Google Scholar, 5Kales S.N. Soteriades E.S. Christoudias S.G. Christiani D.C. Firefighters and on-duty deaths from coronary heart disease: a case control study.Environ Health. 2003; 2: 14Crossref PubMed Google Scholar, 8Geibe J.R. Holder J. Peeples L. Kinney A.M. Burress J.W. Kales S.N. Predictors of on-duty coronary events in male firefighters in the United States.Am J Cardiol. 2008; 101: 585-589Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar In our study, of cases had evidence of LV The autopsy findings from our controls prevalence of heart weight >450 g) that LV hypertrophy and/or cardiomegaly be common among firefighters aged ≤45 research is to screening for cardiomegaly in the fire Our of heavier heart and a fivefold risk increase associated with cardiomegaly in SCD cases, were to be from the obesity in the traumatic controls compared with the occupationally active is not to the heart weight from the active controls, an of obesity in noncardiac fatalities our findings the because obesity usually the heart We that traumatic fatalities occur in obese firefighters because they are to be a fire to their and physical Fatalities among and career 2006; Google Scholar Our study had the NIOSH investigation program have firefighters. about of firefighter deaths were examined by NIOSH from 2004 to compared with of career Smith D.M. deaths among U.S. firefighters: an of fatality 2011; PubMed Scopus Google Scholar for of the United fire National Fire Protection Association, Quincy, Scholar also that the were older as a and of the SCD victims who were aged years were R.F. U.S. Firefighter Fatalities Due to Sudden Cardiac Death, 1995–2004. National Fire Protection Association, Quincy, MA2005: 1-11Google Scholar a of SCD fatalities older cases the NIOSH is to any have to the NIOSH investigations of younger firefighters. of our study was that were to the autopsy in the NIOSH and no standardized were is that our the of obesity or cardiomegaly in young firefighters. our with the from previous that obesity and cardiomegaly increase the odds of D.L. Barr D.A. Kales S.N. Extreme sacrifice: sudden cardiac death in the US Fire Service.Extrem Physiol Med. 2013; 2: 6Crossref PubMed Scopus (102) Google Scholar, 5Kales S.N. Soteriades E.S. Christoudias S.G. Christiani D.C. Firefighters and on-duty deaths from coronary heart disease: a case control study.Environ Health. 2003; 2: 14Crossref PubMed Google Scholar, A.J. Christophi C.A. Burress J.W. Kinney A.M. M. Kales S.N. The obesity and PubMed Scopus Google Scholar, E.S. D. Christiani D.C. Kales S.N. Obesity and cardiovascular disease risk factors in firefighters: a Res. PubMed Scopus Google Scholar, S.N. Christiani D.C. of in firefighters.J Occup Environ Med. PubMed Scopus Google Scholar Our study also had We a case-control with 2 control groups from the same medical data were from conservatively coded the reports from the NIOSH as for the risk factors in the active control Our risk data from the controls have our the The present to previous E.S. Smith D.L. Tsismenakis A.J. Baur D.M. Kales S.N. Cardiovascular disease in US firefighters: a systematic review.Cardiol Rev. 2011; 19: 202-215Crossref PubMed Scopus (297) Google Scholar, 3Smith D.L. Barr D.A. Kales S.N. Extreme sacrifice: sudden cardiac death in the US Fire Service.Extrem Physiol Med. 2013; 2: 6Crossref PubMed Scopus (102) Google Scholar, Fighter Fatality Investigation Reports. National Institute for Occupational Safety and Health, Atlanta2012http://www.cdc.gov/niosh/fire/Google Scholar, A.J. Christophi C.A. Burress J.W. Kinney A.M. M. Kales S.N. The obesity and PubMed Scopus Google Scholar, Smith D.M. deaths among U.S. firefighters: an of fatality 2011; PubMed Scopus Google Scholar, Obesity and among career firefighters in the United 2013; PubMed Scopus Google Scholar, D.L. Firefighter and and Med 2011; PubMed Scopus Google Scholar, D.L. A. M. The prevalence of cardiovascular disease risk factors and obesity in firefighters.J 2012; PubMed Scopus Google Scholar, on for Fire Fire Scholar for medical screening and wellness for because these within the United fire E.S. Smith D.L. Tsismenakis A.J. Baur D.M. Kales S.N. Cardiovascular disease in US firefighters: a systematic review.Cardiol Rev. 2011; 19: 202-215Crossref PubMed Scopus (297) Google Scholar, Smith D.M. deaths among U.S. firefighters: an of fatality 2011; PubMed Scopus Google Scholar In an obesity be because of (1) the prevalence of obesity reported in the present study and in previous R.F. LeBlanc P. Molis J.L. Firefighter Fatalities in the United States–2011. National Fire Protection Association, Quincy, MA2012: 1-36Google Scholar, A.J. Christophi C.A. Burress J.W. Kinney A.M. M. Kales S.N. The obesity and PubMed Scopus Google Scholar, D.L. A. M. The prevalence of cardiovascular disease risk factors and obesity in firefighters.J 2012; PubMed Scopus Google Scholar and (2) our present findings that obesity is associated with an increased risk of cardiomegaly and The also A. and and Harvard Health and Safety for data on of the fire reports as a or independent medical or in and cases, including cases firefighters. reports as a in cases firefighter other potential of to our study