Hierarchical task analysis as a systems mapping tool in complex health care environments: Emergency department response to chemical, biological, radiological, and nuclear events

The emergency department (ED) is at the forefront of the chemical, biological, radiological, and nuclear (CBRN) response. This study adopted a multilevel systems approach using the human factors/ergonomics (HFE) method of hierarchical task analysis (HTA) with document analyses of CBRN plans to represent work‐as‐Imagined. Work‐as‐imagined was compared with data from semistructured interviews using prompt cards for CBRN scenarios (n = 57) representing work‐as‐done. The aim was to provide methodological evidence for the use of HTA with an empirical synthesis of the ED in response to CBRN events. HTA was the preferred systems mapping tool because it aligns with a systems thinking approach, allows multiple‐level comparisons, highlights variability, and has an established usability track record. This study demonstrates the usability of HTA in the context of the ED responding to a CBRN event. The findings for core CBRN concepts included (1) liaise and communicate, (2) isolate and contain, and (3) personal protective equipment.

Complex systems continuously change their interactions with the environment, and their boundaries are difficult to determine.In complex settings, staff often adapt their practices to the varying nature of presentations and gaps in resources.These adaptations often shift away from WAI and represent WAD (Falegnami et al., 2021).
Hierarchical task analysis (HTA) describes a task as a higher-level goal with a hierarchy of superordinate and subordinate tasks (Shepherd, 2001).HTA has been suggested to be an effective way of stating how work should be organized to meet system goals (Kirwan & Ainsworth, 1992).HTA is increasingly used in safetycritical environments such as aviation (Morowsky & Funk, 2016), transport (Wang & Fang, 2014), medicine management (Allitt et al., 2017), and surgery (Demirel et al., 2016;Sarker et al., 2008).
This study used HTA to analyze and unpack WAI and WAD to better understand how two EDs in England respond to CBRN events.WAI versus WAD was used as an overarching framework for thematic analysis.
Although other methods are considered in this study which have been used in a number of complex health care systems research (Hoffman et al., 2009;Sujan et al., 2014) the impetus for using HTA was the simplicity of unpacking a complex environment (ED) during a rare event (CBRN), and adaptability with color coding.It is pertinent to determine whether HTA is a useful method in the ED response to CBRN events, as the methods adopted in this study can be applied to a diverse range of critical health care emergency situations.

| Methodological framework: HTA as an effective systems mapping tool
Most HFE methods were not designed specifically for use in health care systems and have traditionally been used to examine incidents in high-reliability organizations such as aviation, oil and gas, and the nuclear industry (Watt et al., 2019).
HTA has been used to explore and describe health care work, for example in describing the intensive care unit (ICU) as a complex sociotechnical system which is prone to interruptions (Drews et al., 2019).
HTA was anticipated to be advantageous in understanding the ED response to CBRN events because it provided a rapid insight into how first receivers thought tasks should be carried out during a CBRN event.
HTA has been used as an effective method to map out complex surgical procedures (Catchpole et al., 2006;Menozzi et al., 2019).Similar to this study, a triangulation of methods such as a literature review (Razak et al., 2018), observations to form HTA representations of the process, and interviews were used to combine HTA and Systemic Human Error Reduction and Prediction Approach (SHERPA; Corbett et al., 2019) to represent the Functional Endoscopic Sinus Surgery (FESS) technique.SHERPA was applied to the HTA representation to identify errors, for frequency, severity, and potential reduction of occurrence.The combination of HTA and SHERPA was effective to standardize and optimize clinical practice during the FESS procedure.
In this study, HTA was used to provide a systems perspective for a top-down and bottom-up analysis of the complex processes.Other studies (Corbett et al., 2019) used HTA as a bottom-up approach only, with HTA representations formed through participant-driven observations.The research process in unpacking the ED response to CBRN events differs in two ways.First, previous research (Corbett et al., 2019;Demirel et al., 2016) was carried out in operating theaters; although a highly pressured environment, it differs from the ED environment in terms of predictability, team structure and roles, and patient presentations.Second, the research logic of the papers can be questioned, in terms of whether a complete systems representation was being presented.This paper aims to provide methodological evidence for the use of HTA for complex macro-and microlevel comparisons with empirical syntheses of the functioning of the ED in response to CBRN events.The research question asks whether HTA can be used as a versatile tool to compare WAI versus WAD in a safety-critical environment (the ED).
Like the ED, the ICU is described as a complex sociotechnical system which is prone to interruptions (Drews et al., 2019), but it does not have the additional challenge of unpredictability of patient presentations.In this study, HTA was felt to be advantageous because it provided a quick insight into how first receivers thought tasks should be carried out during a CBRN event.This insight links HTA to verbal protocol analysis (VPA), which was used and showed that experienced nurses provided greater insights into clinical decision making when caring for postoperative patients in the ICU (Hoffman et al., 2009).Although VPA is a useful method to collect data, it was felt not to be a suitable method to collect data in the ED because of the unpredictability in the ED compared with the controlled environment in ICU where patient presentations are elective and expected, one-to-one patient care is the norm (one nurse is allocated to one patient).This allows the researcher dedicated access to one nurse for an extended period, with time to record the care process.In the ED, there is a quicker patient turnover, and ED first receivers tend to talk to the patients (in most cases), limiting their ability to think aloud while providing care, making VPA an unsuitable method of enquiry for the ED.
Failure Modes and effects analysis (FMEA) has been used as a practical tool to identify and evaluate risk factors, and propose actions to eliminate risk involved in care processes in the ICU (Askari et al., 2017;Faye et al., 2010).However, one of the issues with this method is that it is reported to be time consuming and resource intensive (Bevilacqua et al., 2015) and with the unpredictability and complexity of the CBRN response it was felt not to be suitable for this study.Sutherland et al. (2019) used HTA as part of the SHERPA to enhance the care provided to patients in the complex pediatric intensive care unit (PICU) environment while highlighting multifactorial and contextual factors associated with prescribing errors.
SHERPA is based on HTA (first step) and then goes further with an analysis of human error, whereas this study aimed to explore whether HTA was a suitable method to map complex sociotechnical systems rather than explore error opportunities.
It is evident that HTA can be applied in different health care settings to understand processes and be combined with other methods (e.g., SHERPA).The ED is a uniquely unpredictable complex environment and CBRN events are a rare and real threat, with the potential for detrimental outcomes if not responded to adequately.
For clarity in such a complex environment, HTA was used as a single HFE method for simplicity and detail.

| MATERIALS AND METHODS
This paper describes how HTA was applied to better understand ED response to CBRN events in two hospitals in England by comparing Data were collected in two types one EDs: a "consultant led 24 h service with full resuscitation facilities and designated accommodation for the reception of accident and emergency patients" (NHS Data Dictionary, 2017).ED-A served a population of 1 million residents and the hospital specialized in cardio-respiratory diseases, cancer, and renal disorders.ED-B served a population of 600,000 residents and the hospital specialized in inpatient and outpatient surgical and medical specialities, intensive care, maternity services, children's services and accident and emergency care, vascular, cancer, and stroke care.ED-A employed 15,000 staff, whereas ED-B employed just over 8000 staff.The last CBRN event ED-A response was for a white powder incident in 2004 and ED-B responded to the accidental contamination from an industrial site in 2018.ED-A treated 237,000 patients and ED treated 116,000 patients during the study period (2016)(2017).
The study design was divided according to the HFE theoretical framework of WAI (document analyses of CBRN Plans) and WAD (interview response to scenario cards).The data collection process used a qualitative methodological approach with both inductive and deductive logic, to move between sources of information as illustrated in Figure 1.
In the WAI (top-down) component, CBRN plans were converted to HTAs.These were verified by CBRN planners at both EDs to ensure that subject matter experts participated in and informed both the data collection and analysis process (Hignett et al., 2005).The HTAs were also reviewed by HFE experts to check for inconsistencies.
The WAD (bottom-up) phase had two phases of data collection, both using semistructured interviews.The first phase collected data about WAD, with participants recruited on varying ED shifts at both hospitals including week-day day shifts, weekend day shifts, weekday night shifts, and weekend night shifts.Scenario cards (Figure 2) were presented at a convenient time when the identified first receiver was available.Scenario cards were based on National CBRN Guidance (Health Protection Agency, 2008) and reviewed by a Hazardous Area Response Team specialist to ensure that they were realistic.The participant was presented with the scenario card in the ED, given time to read it, and then asked to describe their actions when faced with the scenario.Probes were used to expand on responses with "what, why, and who" questions.The interviews lasted approximately between 5 and 15 min.Field notes were made which were transcribed (for record-keeping and analysis) and converted to HTAs.
The second (WAD verification) stage, followed the guidance from Stanton (2006) to confirm the reliability of the HTA to represent the data correctly.The verification process was carried out on a separate occasion and began by providing the first receiver with the scenario card as a memory aid.The functions of HTA were then explained and the participants were given time (approx.3 min) to review the HTA.The first receiver was then asked, "Do you think this diagram is a true representation of what you would do in a CBRN event?" with the opportunity to discuss and amend the HTA.This phase of the study was carried out in a quiet room with each interview lasting 10-25 min.WAI and WAD HTAs were then colorcoded based on themes formulated from applied thematic analyses.
Intra-rater reliability was reviewed during the thematic analysis process to check for interviewer (S.R.) bias or leading prompts.This was further reviewed during the HFE expert check for inconsistencies.As there was only one interviewer, inter-rater reliability was not relevant.S. For the verification (member checking) interviews (n = 20), first receivers were selected from the first stage (WAD interviews) using stratified purposive sampling to compare, contrast, and identify similarities and differences in the phenomenon of interest (Palinkas et al., 2015).This group comprised of eight nurses, four doctors, two security officers, two HCA's, two receptionists, one porter, and one medical physicist (mean age 43 years, range 24-58 years, mean length of ED employment 9 years, range 3 months to 20 years, 10 males and 10 females).This was combined with the percentage RAZAK ET AL.

R. attended NHS Good Clinical
| 149 distribution to keep consistency as well as provide representative verifiers for the HTAs.

| Analysis and synthesis
Data were recorded through field notes which were transcribed and converted to HTA representations.These were thematically analyzed and then color-coded to facilitate visual comparison of themes.The combination of applied thematic analysis (Guest et al., 2014 operations (Embrey et al., 2009).Color coding has also been used to identify actions involved in prescribing drugs in the complex PICU (Sutherland et al., 2019); color coding in these studies was combined with HTA for descriptive purposes to show different tasks.The color coding of HTAs to unpack the ED response to CBRN events was used differently-to augment the thematic analysis with a visual representation to aid the review process.
Applied thematic analysis takes a pragmatic approach by using appropriate tools to achieve the analytical goal in a transparent, efficient, and ethical manner.It can be used with different types of qualitative data (e.g., field notes, transcripts, and HTAs), and with more applied research.The CBRN response required practical action from the first receivers.

| Rigor and credibility
Rigor is relevant to the reliability, validity, and reduction of bias in qualitative research (Bowling, 1997) tasks are generic in ED-B (Figure 4).One key difference between both EDs is the importance place on documentation, ED-A frame documentation as a legal requirement, whereas documentation is not a priority in ED-B.Another key difference is the importance placed on decontamination, in ED-A it is a higher-level task, in ED-B it is not.
The recovery phases are variable in both EDs with "Debrief" being a characteristic of ED-A.
The action card HTAs were different between the EDs for stages 3 and 4 of response: (1) Prepare to respond to CBRN incident (ED-A and B).
Finally, there was a difference in the total number of GOR themes; ED-A had 13 GOR themes and ED-B had 20 GOR themes, with 13 overlapping themes including decontaminate, personal protective equipment (PPE), clinically assess, and triage.ED-B had additional GOR themes for consider capacity and patient flow, provide equipment/stock, and base response on incident type (major incident or CBRN event).

| WAD
NICs at ED-A managed CBRN presentations by taking the lead while protecting their team and the environment through responses such as: "Restricting people going in, limit to the assessment nurse and doctor going into the patient, seal off, and evacuate the department" (ED-A NIC).Early care nurses implemented crucial CBRN actions such as isolate and contain.It was found that there was a lack of focus on the importance of carrying out decontamination amongst band six nurses across both ED's.All doctors made decisions at ED-B, however, senior doctors additionally secured the department and managed staff.
Similarities between the EDs were found for the importance placed on actions for isolate and contain, liaise and communicate, and escalate.
Differences were found for the importance of PPE, decontamination, treatment, and investigation of the presentation (Table 1).
The similarities identified for WAD result in a bottom-up perspective to consider standardization based on WAD (how first receivers respond to CBRN events).This study found that WAI focuses on actions such as documentation, checking, timing, and providing equipment, whereas WAD and first receivers prioritized patients' needs through assessment, treatment, and diagnosis.Table 1 illustrates that along with variability on the organizational response, there exists differences on key CBRN tasks such as decontamination; which is a key task for ED-B staff, and is not mentioned in ED-A frontline responsibilities, however, decontamination is a high-level organizational task for ED-A Figure 3.  thematic analysis.Themes were given specific colors to allow detailed mapping of the CBRN process.For example, Figure 5 illustrates how the PPE theme (green) was included in the GOR of the ED-B CBRN plan; the visualization assisted with the comparitive analysis.Figure 5, is a hierarchical representation of PPE which was core to both the GOR and individual first-receiver action cards.For example, PPE was a part of preparing the infrastructure and equipment in ED-Bs GOR as shown in Figure 5.The implementation of PPE was mentioned on one action card (P1 lead doctor: Figure 6).

| WAI versus WAD in the ED response to CBRN events
PPE was also discussed in the WAD responses by ED-B doctors as shown in the synthesis HTA (Figure 6).
The implementation of PPE is used as an example of how HTA was able to unpack, compare, and enhance the ED CBRN response.
Donning (putting on) PPE would form the preincident phase in Figure 4 (p.8) under 2. Prepare for incident.PPE was not prioritized until high-level task 6. Carry out required decontamination procedure; suggesting that although a part of the higher-level tasks, staff would not don PPE until after a CBRN event was declared, whereas ED-B would be donned.HTA has allowed to identify variability both in tasks, and prioritization of response processes it has also highlighted that there is an importance in the order of the execution of tasks.

| DISCUSSION
This paper aimed to provide methodological evidence for the use HTA for complex macro-and microlevel comparisons with empirical syntheses of the functioning of the ED in response to CBRN events.
This paper clearly evidenced that HTA was a versatile and dynamic tool to make top-level and granular analyses, which resulted in opportunities to unpack, understand, and enhance the ED response to CBRN events through the standardization of time-critical processes.Using HTA identified core CBRN concepts: (1) liaise and communicate, (2) isolate and contain, and (3) PPE.
The ED is a complex sociotechnical system (CSS) (Braithwaite et al., 2017), in which groups of people such as patients, relatives, and clinicians interact with different technologies in various physical and organizational environments (Catchpole, 2006;Effken, 2002).CSSs  (Razak et al., 2018).
The adaptability and effectiveness of HTA as a systems mapping tool are discussed in the context of health care as a complex, dynamic, and interdependent system based on patient variability and multiple care interactions (Vosper et al., 2018).HTA was chosen because it is a flexible technique that can be used to describe any system (Kirwan & Ainsworth, 1992).It was used as a stand-alone method to provide a rapid and rigorous analysis of the care processes in the ED.
It is noted that HTA forms the initial stage in other methods, including, CTA, AH, WDA, VPA, and Event Analysis of the Systemic Team (EAST).Although this study adopted a number of methods EAST framework (Stanton et al., 2008), is an example of a method that is useful for examining performance in complex systems.An applicable advantage of EAST to the ED CBRN response is that it is generic so that it can be used to evaluate activities in number of domains.EAST also incorporates key HFE components such as situational awareness, decision-making, teamwork, and communications (Stanton et al., 2018).EAST would be applicable to the microcomponents of this study (Figure 7, p. 13) in terms of nontechnical aspects of the ED response to CBRN events.
Another applicable method to this study is the Networked Hazard Analysis and Risk Management System (NET-HARMS) (Dallat et al., 2018).NET-HARMS provides a compact framework to allow practitioners to (1) Identify risks across the overall work system and (2) Understand emergent risks that are a result of risks across the system interacting with one another.NET-HARMS could be used to streamline the analyses to highlight risks and how these risks interact with one another in both macro-and microanalyses of the ED CBRN response.Providing a highly valid template to identify and eliminate risks in emergency responses (Dallat et al., 2023).
CTA provides insights to cognition which could be useful in adaptive feedback mechanisms and models the hierarchical safety control structure present in the system to implement safety constraints (Leveson, 2011) was used to understand the application of an HFE-led systems approach to health care incident analysis by Canham et al. (2018) focusing on a medication error incident involving two health care providers in the United Kingdom.STAMP was effectively used to guide health care stakeholders towards consideration of system design issues and remedial actions.Applying these findings to the current study, STAMP can be used as a second analyses method to investigate CBRN responses.
WDA is a framework that defines the work demands of complex sociotechnical systems in term of constraints placed on people in the system.Although a useful method for improvement, it is vital to have an understanding of the complex sociotechnical system.Like HTA, WDA can be used to provide a better understanding of how complex health care environments like the ED function, however, there still exists a void in ED systems and ED design (Read et al., 2018).It has been recommended to combine WDA with another method, for example, abstraction hierarchy to identify and produce new ED design concepts.Similar to this study, HTA was combined with a number of methods (Interviews, color coding, and thematic analysis) to provide recommendations to enhance the ED CBRN response.
Mapping out a rare event (CBRN) in a complex clinical setting (ED) is challenging as a result of the pressure, unexpected presentations, fatigue, and being constantly short-staffed.The patients are often unpredictable and treatments often delayed to technical as well as environmental factors.HTA was considered the optimal method to unpack the ED CBRN response, and even more so make a comparison between two ED's.WDA is often used as a method to identify features of health care work systems that should be considered when planning improvement and interventions (Sutherland et al., 2022).Although WDA can be applied to identify variations and constraints between EDs, once ED's have been mapped out individually and analyses standardized, a WDA can be carried out for future enhancements as well as develop a detailed model of a generic CBRN response as demonstrated by Salmon et al., while identifying issues which could prevent a successful return from lockdown.HTA was adaptable to all components of the ED CBRN response due to its adaptability to micro, meso, and macro components, hence being chosen over WDA as an initial analysis.
FRAM (Hollnagel, 2004) which was initially proposed as an alternative way to analyze accidents in complex systems, including aviation (Hollnagel et al., 2008) and operating theaters (Woltjer, 2010) was considered as a relevant method due to the concept of variability in this study.
FRAM elicits information about how variations in the performance of individuals, technology, and organizations impact accidents in complex sociotechnical systems (Hollnagel et al., 2008) and was considered to be used in this work.FRAM uses the concept of functions which are the means needed to achieve a goal and defines sociotechnical systems through the functions they perform rather than by their structure (Hollnagel, 2004).This categorization limits the applicability of FRAM in this research because the ED CBRN response is defined by both (organizational) structures such as adhering to instructions by Command-and-Control teams as well as departmental and individual (first receiver) functions.Therefore, FRAM would jeopardize obtaining a complete functional and structural understanding of the ED response to CBRN events.
Hence, HTA was chosen to represent both the structure and function of the ED CBRN response.FRAM did not offer the multilayer versatility that HTA offered, the ED CBRN response is multifaceted, it needed a simple yet rigorous method to understand, break down, and standardize key components of the ED CBRN response.
Although, FRAM focuses on variability in policy and practice, it is daily policy and practice.The context of this study is responding to a CBRN event, which consists of tasks that are not daily practice, in fact, consist of tasks that are rare such as donning and doffing powered respirator protective suits and wet decontamination.
Therefore, although FRAM takes into consideration crucial principles such as variability and WAI and WAD, HTA served to be a better method in this context because it shows an understanding of how tasks are organized in terms of levels and how they can be structured.
Whereas FRAM represents necessary functions to carry out the target activities, which in this context are already known through CBRN plans (Hollnagel, 2018).
The WAI versus WAD framework provided a robust theoretical framework to identify gaps and improvement opportunities in the ED CBRN response.Accordingly, HTA has been demonstrated to be a versatile tool to compare WAI versus WAD in the ED CBRN response.This paper provides methodological evidence for the use RAZAK ET AL.
| 155 of HTA in complex multilevel comparisons, and as a tool to address and streamline variability to enhance the ED CBRN response.This study provides empirical evidence to show that the method of HTA can be used to unpack a multifaceted event in a complex environment, and is versatile enough to be used to better understand other time-critical processes such as the Sepsis framework, responding to Diabetic Keta Acidosis, as well as being applied to mental health crises.

| Limitations
While this study makes contributions to existing research it is important to acknowledge the methodological limitations.
Transferability in qualitative research is equivalent to external validity in quantitative research (Ferguson, 2004).The transferability of findings can be questioned because the study was carried out across two NHS type one EDs in the Midlands region of England, which limits the generalizability of the findings on an organizational and regional level.Transferability can be confirmed by providing thorough descriptions of the research context and research environments (Hayre & Muller, 2019).This was ensured through ethically approved protocols which contained rich descriptions of the ED's.
Study data were generated from a purposive sample at a single point in time, document analysis was carried out on CBRN plans, which are reviewed and revised bi-yearly, and clinical guidance which formed the scenario cards had been updated, therefore the analysis could be considered "out of date" once the plans and guidance were updated.
A limitation of HTA is, if used as a standalone method, it will describe the CBRN process rather than explain it.However, it was decided that HTA was the most appropriate method for the following reasons: • The ED is a complex and unpredictable environment in which "quick" data collection methods must be implemented.
• CBRN events are multifaceted situations that require a simple method of effectively unpacking to enhance understanding and communication.
• HTA provided a consistent method for top-down and bottom-up analyses and has been used in other HFE health care projects.
The ED is a uniquely unpredictable complex environment and CBRN events are a rare and real threat, with the potential for detrimental outcomes if not responded to adequately.For clarity in such a complex environment, HTA was used as a single HFE method and provided ample information for comparison and recommendations for enhancing how the ED responds to CBRN events.

| CONCLUSION
The aim of this study was to provide methodological evidence for the WAI and WAD.It uses HTA with thematic analysis and then colorcoding to facilitate visual comparison of themes to explore differences between WAI and WAD.Ethical approval was received from the Loughborough University subcommittee (C17-22) with Health Research Authority (HRA) approval granted through the Integrated Research Application (IRAS) (219968) and Research and Development (R&D) approval from both hospitals.
Practice training, Informed Consent Training and Site File Training before carrying out the interviews.A total of 57 participants were recruited (30 females and 27 males).Roles included: 12 doctors, 21 nurses, 8 Health Care Assistants, 8 Receptionists, 4 security officers, 2 porters, 1 medical physicist, and 1 ED Assistant.Ages ranged from 21 to 60 years (mean = 39 years, SD: 10).Participants were employed by the NHS in a different role or different department for an average of 12 years (SD: 8).The length of employment in the ED ranged from 3 months to 20 years (mean: 8 years, SD: 5).
) and color coding to both the field notes and the HTA representations of responses resulted in themes, which consisted of actions crucial to responding to a CBRN event.Color coding has previously been combined with HTAs for highlighting various purposes.For example, color coding has been used to highlight initial tasks and plans for predicting and preventing human errors in safety-critical plant F I G U R E 1 Representation of human factors/ergonomics components of the study relative to methods implemented.CBRN, chemical, biological, radiological, and nuclear; ED, emergency department; HTA, hierarchical task analysis; WAD, work-as-done; WAI, work-as-imagined.
Figures 3 and 4 illustrate the variability between the organizational response frameworks between ED-A and ED-B.The preincident phase is shorter in ED-A, consist of "1.Understand roles and responsibilities," whereas, ED-B consists of two preparatory tasks.The incident phase in ED-B, however, is shorter, with ED-A consisting of five separate tasks and ED-B having three tasks in this phase.The tasks are granular in the incident phase in ED-A while the response Multiple analyses were possible by combining HTA representations of WAI and WAD, with color coding as data visualization for the F I G U R E 4 ED-B: general organizational responsibilities superordinate tasks.ED, emergency department; CBRN, chemical, biological, radiological, and nuclear.T A B L E 1 WAD results.
have been associated with unexpected variability in performance in which patient safety can be compromised(Saurin & Werle, 2017).The complexity of the ED combined with a rare occurring event, with the stresses of the ED in terms of it being a time-critical environment (4-h breaches), short staffing, and a proportion of bank and agency F I G U R E 5 Personal protective equipment theme (green color) in general organizational responsibilities (ED-B) (work-as-imagined).ED, emergency department; PRPS, powered respirator protective suit.F I G U R E 6 Personal protective equipment theme (green color: Task 1.2.) discussed by ED-B doctors (work-as-done).ED, emergency department.RAZAK ET AL. | 153 staff add to this complexity primarily because they are unfamiliar their environment, processes, and clinical demands (Appleby, 2019).HTA was a valuable tool to recognize CBRN response nuances in established emergency organizational responses as well as operational responses.HTA established that although these were the accepted responses, there existed a large degree of variability, which could be detrimental to an effective response.Variability is a lack of consistency in clinical practice and processes-variability in practice between health care organizations, departments, and even amongst clinicians pose challenges to responding to rare CBRN events.A means of streamlining emergency responses for staff who are unfamiliar with their environment and clinical expectations is that of standardization.Standardization overcomes variability by "Setting formal rules to guide employees 'activities, which are operationalized in organizations by means of work instructions, guidelines, manuals, and work procedures" (Nissinboim & Naveh, 2018, p. 44).Standardization aims to embed best professional practice, while minimizing the risks of variation, consequently maximizing consistency of actions across teams, organizations, and the health system (NHS England, 2014).The findings of this study are that variability exists between 2 NHS EDs in England, with reference to the CBRN response.Variability was evident in the (1) differences in the number of first receivers included in the response, (2) having different nursing roles across hospitals, (3) having unspecified banding/experience for CBRN roles, and (4) differences in number of phases in the CBRN response.The implications of ED CBRN response variability on staff, and particularly locum/bank and agency staff are that they will have conflicting guidance on how to provide safe and effective care during a CBRN event.This variability can also have negative consequences on substantial staff as they are distracted because they are required to "manage" nontemporary staff (Bajorek & Guest, 2019), adding to their demanding workload.It is also reported that temporary staff who are familiar with their work environment are favored more so than those that are unfamiliar.HTA was effective in allowing top-down (macro) and bottom-up (micro) analyses in the ED CBRN response as illustrated in Figure 7.The analyses allowed the identification of micro-, meso-, and macrolevel differences.HTA was used at macro-(CBRN Framework and policies/procedures) and micro-(operational activities: action cards) and ED team working (mesosystem) with multiple analyses to provide a comprehensive analysis and representation of the ED response to CBRN events (Figure 8).A means of overcoming various discrepancies is by providing standardized and streamlined guidance or set of CBRN algorithms as are prevalent in time-critical safety situations, examples include Anaphylaxis and Life Support guidance by the Resuscitation Council UK (Resus.Org, 2023) as well as CBRN response planners checklists

F
I G U R E 7 Multiple level analyses, interpretation, and comparison through HTA.CBRN, chemical, biological, radiological, and nuclear; ED, emergency department; GOR, general organizational responsibilities; HTA, hierarchical task analysis; WAD, work-as-done; WAI, work-as-imagined.F I G U R E 8 Multiple systems in the emergency department chemical, biological, radiological, and nuclear response.
enhancing response, particularly through training.For example, Chan et al. (2016) used CTA to enable doctors to prioritize patients in simulated patient environments, in turn, being a resource for clinical educational materials.Additionally, in line with the recommendation to standardize the ED CBRN response, Guo et al. (2021), used CTA to used CTA to create template case reports as a means of enhancing their emergency thinking ability through standardized training; Suggesting a combination of CTA and HTA to both unpack and standardize ED CBRN training.Systems Theoretic Accident Modeling and Processes (STAMP) describes an accident in terms of a hierarchy of control based on use of HTA with an empirical synthesis of the ED in response to CBRN events.It has been demonstrated that HTA is an effective HFE method that allows multiple comparisons and is a versatile tool for use in a safety-critical health care environment.Most importantly HTA as provided the granular analyses which highlights the variability in multiple layers of the ED CBRN response.A means of overcoming this variability with particular implications for temporary staff such as doctors, nurses, and HCA's who constantly move around different EDS, is that of standardization of the organizational CBRN response as well as the standardization of key response processes.There were differences in priority and importance placed on numerous tasks, this variability extended to having specific responders in one ED and not in the other, the Medical Physicist role exemplifies this, as there was a medical physicist in ED-A and not in ED-B, in fact there was no radiological cover for ED-B CBRN response.Based on these pertinent nuances for CBRN responses, the ED CBRN response is in need for standardization, for familiarity with a rare event, as well as high-quality care being delivered in an unfamiliar context.HTA in this context highlighted the negative effects of variability and provided a solution of standardization particularly for temporary staff who move around various EDsThe WAI versus WAD framework provided a robust theoretical framework to identify gaps and improvement opportunities to prioritize a safe work environment for first receivers to provide high-quality care to patients during a CBRN event.HTA is an effective system mapping tool, which can be used alone or (where appropriate) in combination with other HFE tools to unpack a multifaceted event in a complex environment.The use of color coding for visualization of the thematic analysis made a useful contribution to enhance the usability of HTA as a systems mapping tool in health care.The analysis and results identified key CBRN concepts which include the importance of sharing information through uncategorized and extended communication means, isolate and contain, and the ambiguity and variability associated with PPE.CBRN events are timecritical situations; in which the clinical and organizational skills of first receivers should be prioritized to deliver safe and concise patient care.A means of achieving this could be to standardize the CBRN response in NHS hospitals.Future work can be used to develop standardized ED CBRN training materials through using CTA.STAMP can be implemented to investigate CBRN responses with future enhancements being applied to CBRN responses through WDA.