Firefighters occupational exposure assessment: a systematic literature review

Introduction: Over the years, the evolution of forest fires has occurred as a result of the evolution of the human species. However, forest fires are still a major challenge for society, placing firefighters with greater occupational exposure. The present study has as main objective to carry out a systematic review of the literature on the main techniques and variables for assessing the occupational exposure of firefighters, during the fight against forest fires. Methodology: The systematic review utilised The Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement methodology. This methodology was applied in the Scopus, Web of Science, Pubmed and Academic Search Complete databases with different keywords. The review will include articles written in English only. Results: In the present study, 34 articles were included, in which it was found that exposure to smoking is the most studied variable, and it was in 2019 that a greater evolution of studies in this area of research was observed. Regarding the variables, the studies were organised in groups. Here it is possible to check the different variables selected by the authors and the methods and equipment applied. Discussion: The fact that firefighters carry out their tasks in diverse scenarios and extreme conditions has hindered the application of innovative equipment. It is necessary to combine different variables and equipment for the assessment of occupational exposure. However, it is not always possible to develop this type of equipment in order to be inserted from the user's perspective, from the perspective of the environment, where it will be applied, and from an economic perspective, making it difficult to effectively apply it in the field. Conclusion: As future perspectives, it is recommended that new variables are introduced together, in order to improve the assessment of occupational exposure, namely, through the use of carbon monoxide (CO) and lactate assessment.


INTRODUCTION
In 2018, Portugal accounted for 467 fire brigades and 27649 firefighters (PORDATA, 2018).The climate changes that have been taking place in recent years, have made fighting forest fires more difficult and time-consuming, making Portugal one of the countries with the highest forest fire risk ranking.Some large fires are already known that have caused high numbers of deaths in firefighters (Viegas, 2017).The performance of firefighters' activities in front of a fire is physically and mentally demanding, exposing individuals to heat, fatigue, stress, noise and exposure to chemical substances, through inhalation and dermal contact (Broyles et al., 2019;Neitzel et al., 2009;Serra et al., 1996;Swiston et al., 2008).
The toxic agents that are often found in smoke from forest fires and that are known to cause major impacts on the respiratory tract are Carbon Monoxide, Formaldehyde and Respirable Particles (Neitzel et al., 2009).Studies of the impacts on the health of forest fires have used different aspects and research methodologies.One of the variables that have been extensively studied is the acute toxicity of smoking.Exposure to smoke from forest fires is equivalent to exposure to tobacco smoke.It is a smoke with mixtures of polycyclic aromatic hydrocarbons (Adetona et al., 2017;Nathaniel Rothman et al., 1993).
Forest fires are still a major challenge for a society, where the area of investigation of the occupational exposure of firefighters demonstrates a strong need to be further developed and built, in order to reduce the negative impacts that this area has on the community (Miranda et al., 2010).The aim objective of this study is to carry out a systematic review of the literature on the main techniques and variables for assessing the occupational exposure of firefighters, during the fight against forest fires.

METHODOLOGY
For the systematic literature review, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement methodology was adopted.The research strategy was developed based on the extension of the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P).The research focused on the SCOPUS, Web Of Science, Pubmed, and Academic Search Complete databases.There were no date restrictions on the selection of articles, and language selected was English.The selected keywords were: Firefighters, Forest Fire; Occupational Exposure; Occupational Health; Occupational Exposure Limits; Occupational Hygiene; Work Injuries; Professional Diseases; Cognitive Function; Occupational Safety; Subjectivity of Perceived Effort; Fatigue; Physiological Response; Physiological Monitoring; Stress and Occupational Innovation.All articles with samples of firefighters were included, without age or sex restrictions.Articles with field and laboratory methodologies applied exclusively to forest fires and with samples of firefighters were accepted.After selection in the databases, the articles were analysed and selected by the abstract.Finally, the methodology of each article was analysed, identifying the variables used and the main results.

RESULTS
A total of 369 articles were obtained, which, after applying the filters in each database, resulted in 329 articles.Of these, only 34 articles were included in the methodology and for eligibility criteria.In Table 1, it is possible to verify the articles selected in different steps, including the filters applied.In 2019, there was a peak in this area of investigation, and the keyword corresponding to this peak is "Occupational Exposure".In Figure 1, it is possible to check the selection of articles using the prism diagram.With regard to variables, the studies were organised into groups, namely stress, exposure to smoke (here included articles referring to exposure to carbon monoxide (CO), respirable particles (PM), formaldehydes, radionuclides and hydrocarbons), exposure noise, lung function (including articles referring to respiratory symptoms), exposure biomarkers, thermal stress, cancer, nutrition and hydration, workload and cognitive function.In Table 2 it is possible to verify the variables used by the different authors and the techniques applied.

DISCUSSION
In the results of the present study, it is verified that only one study mentioned the evaluation of radioactivity compounds.The assessment of exposure to radionuclides emitted by smoke during a forest fire can be used as an indicator of cancer incidence, in particular lung cancer.However, it is known that the appearance of lung cancer in firefighters can originate from the combination of different variables, such as exposure to smoking and smoking habits (Abreu et al., 2017).
The International Commission on Radiation Units and Measurements (ICRU) provides international recommendations regarding acceptable values, applicable units and radiation measurement techniques.The techniques for assessing radiation exposure have evolved to ensure greater accuracy and assessment of exposure (International Commission on Radiation Units & Measurements, 2021).However, the measurement in real-time in a forest fire proves to have great difficulty in the application of equipment and the innovation of the process of sampling.In this way, some ways of assessing radioactivity are known through the use of autonomous large-volume samplers, portable aerosol samplers (Carvalho et al., 2014), by estimating the effective dose by inhalation using the Gaussian model (Viner et al., 2015) or through the use of other models.These authors use the Linear No-Threshold model to assess the risk to human health of a forest fire in a forest with radiological contamination.
The use of systems to monitor the health status of firefighters in real-time has already begun to be developed.However, these systems have not yet been applied to all activities at greatest risk to firefighters, as they are not yet developed with variables that indicate enough information to assess the health status of firefighters during the execution of the activity.In fact, the assessment of the firefighters' health status and, consequently, their occupational exposure does not always involve a large number of variables, as can be seen through the included studies, where the variables that are mostly included are related to smoke exposure, thermal stress and lung function (Jose A. Rodríguez-Marroyo et al., 2012).
In a study by Raj & Sarath (2019), a prototype was created that allows the assessment of firefighters' stress through the application of wireless sensors on gloves.In fact, physiological monitoring by wireless systems is an important step towards the safety of firefighters.The information that is provided by these systems allows the assessment of the person's health status, as well as their state of readiness (Adetona et al., 2011;Neitzel et al., 2009).
The collection of data related to the environment in which the firefighter is extremely important.Data such as ambient temperature, CO and oxygen levels allow assessing of the physical circumstances that are conditioning the firefighter's safety and can be warning indicators when these conditions are not those recommended for the health of the professional.These telemetry sensors for monitoring firefighters, together with physiological variables, are already known (Henn et al., 2019;Navarro, Kleinman, et al., 2019;Raines et al., 2012;West et al., 2019).The combination of environmental and physiological variables may prove to be the key to the indication of fatigue alerts caused by exposure to the occupational environment of forest fires.
In fact, physiological variables are already known which, when exposed to certain environments, represent fatigue indicators.An example of this, lactate, which has been shown to be an important and easy to monitor indicator, has already been verified as an innovation in biotelemetry.Lactate is already used to determine pathologies and determine the bioenergetic consumption of muscle cells.The correlation between the increase in lactate concentration and exposure to environments with high concentrations of CO, allow us to indicate lactate as a good indicator of overload since it is associated with the consumption of oxygen for energy production, verified that in oxygen-deprived environments the lactate concentration tends to increase.Therefore, lactate is considered an invasive parameter that can be difficult to include in biotelemetry systems.Assuming that the anaerobic threshold can be estimated using heart rate, a parameter that is easy to measure using portable meters and that although it is known the need for more evaluations to determine the agreement of the different variables (Apud & Meyer, 2011).
Note that other variables of physiological stress should also be included in the occupational assessment and in the combination of those previously mentioned, such as, for example, the assessment of cognitive function (Navarro, Cisneros, et al., 2019).Although it is not easy to apply tests to assess cognitive function in real-time, except at the end of firefighting or in a laboratory environment, some tests are already known that allow easy evaluation.

CONCLUSION
As we have seen, innovation in firefighters has proved to be difficult to apply.The fact that firefighters carry out their tasks in diverse scenarios under extreme has made it difficult to apply innovative equipment.In addition, some of the equipment developed is not economically sustainable, making it a major obstacle to acquiring such equipment by the fire brigades, particularly in Portugal, where they are mostly non-profit corporations.The development of this equipment must be thought from the user's perspective, from the perspective of the environment where it will be applied and from an economic perspective.However, it is not always possible to develop innovative equipment that falls within these three perspectives, making it difficult to quickly and effectively apply it on the ground.

Table 2 .
Variables and apllied techniques