RESOURCE ARTICLE

Using [2_TD$DIFF]bowtie methodologyto support laboratoryhazard identification, riskmanagement, and incidentanalysis

[36_TD$DIFF]Mary Bethe U.S.PennsylvWashing

Chris BoGL, 14077449, U

SamuellA.R. SmAppalacRivers S

Ralph Stmental HCollege [41_TD$DIFF],03435-2Tel.: +1(E-mail:

14 �A

Hazard prevention and control systems for specific laboratory processes must be readily shared between labworkers, their colleagues, and lab supervisors. In order for these control systems to be effective in atransferable and sustainable way, effective risk management communication tools must be present. Thesetools need to be adaptable and sustainable as research processes change in response to evolving scientificneeds in discovery based laboratories.

In this manuscript, the application of a risk management tool developed in the oil and gas industry knownas a ‘‘bowtie diagram’’ is assessed for application in the laboratory setting. The challenges of identifyinglaboratory hazards and managing associated risks as well as early experiences in adapting bowtie diagramsto the laboratory setting are described. Background information about the bowtie approach is provided andthe technique illustrated using an academic laboratory research scenario. We also outline the role bowtiediagrams could play in a proactive safety culture program by facilitating hazard communication andmaintaining hazard awareness across a wide spectrum of stakeholders.

By Mary Beth Mulcahy,Chris Boylan,Samuella Sigmann,[3_TD$DIFF]Ralph Stuart

th Mulcahy is affiliated withChemical Safety Board[37_TD$DIFF], 1750ania Avenue, NW, Suite 910,ton, DC [38_TD$DIFF]20006, USA.

ylan is affiliated with DNV0 Ravello Drive, Katy, TXSA.

a Sigmann is affiliated withith Department of Chemistry [39_TD$DIFF],hian State University [40_TD$DIFF], 525treet, Boone, NC 28608, USA.

uart is affiliated with Environ-ealth and Safety Keene State

229 Main Street, Keene, NH502, USA.802 316 9571rstuartcih@me.com).

2017 Division of Chemical Health and Safety

ll rights reserved.

A series of highly publicized incidents

[4_TD$DIFF]INTRODUCTION

have highlighted the physical hazardsof energetic, pyrophoric, and flamma-ble materials used in academic re-search laboratories.1–3 Theseincidents have brought attention tothe challenge of safely managing themultiple, rapidly-evolving chemicalprocesses that are characteristic ofthe laboratory environment. To keeppace with this evolution, the Associa-tion of Public and Land Grant Univer-sities (APLU) has suggested that a newapproach to laboratory safety is re-quired. The APLU suggests that thenew approach should address bothtechnical and cultural aspects of thisissue.4 Several hazard identification,evaluation, and management toolshave been described in the NationalAcademy’s Prudent Practices in theLaboratory and the American Chemi-cal Society’s publication Identifyingand Evaluating Hazards in ResearchLaboratories to address the technicalside, but the cultural aspect of the

of the American Chemical Society. Published by Elsevier Inc

challenge requires that risk manage-ment knowledge must be readilyshared between laboratory workers,their colleagues, and administrators.5,6

To be effective, risk assessment andcommunication tools must also beadaptable to research processes as theychange in response to evolving scien-tific needs.

SAFETY MANAGEMENT IN THELABORATORY SETTING

Academic laboratories host many dif-ferent operations serving a variety ofpurposes. Teaching, research and ser-vice laboratory functions are routinelyintermixed with personnel moving be-tween them as needs arise. This diver-sity in laboratory operations is asignificant challenge when addressingsafety management in this setting.

Academic laboratories are quite di-verse in scope and activities. For thepurposes of this paper, ‘‘laboratories’’refer to workplaces that conform to the

. 1871-5532

http://dx.doi.org/10.1016/j.jchas.2016.10.003

Occupational Safety and HealthAdministration’s (OSHA’s) definitionof laboratory ‘‘scale and use’’ definedin 29 CRF 1910.1450.7[5_TD$DIFF] In these labora-tories, diverse chemicals are used inmultiple processes in quantities thatone person can safely manipulate usingtraditional laboratory safety practices.These practices include generic engi-neeringcontrols suchas laboratoryven-tilation and chemical storage devices,emergency response equipment, work-er training and oversight, and personalprotective equipment. It is important toremember that many research activitiesin higher education go beyond this def-inition by involving significant non-chemical hazards, using amounts ofchemicals beyond OSHA’s definitionof laboratory scale, orby using materialsfor which insufficient hazard informa-tion is available.

As noted by both the US ChemicalSafety Board (CSB) and the NationalResearch Council (NRC), the tradi-tional laboratory safety model is beingchallenged in the modern academiclaboratory.1,8 Emerging factors, suchas the increasing turnover and diversi-ty of laboratory workers, and the crea-tion of new materials with unknownhazards, have rendered the traditionallaboratory safety practices listed aboveinadequate, taken alone, for addres-sing research hazards. Preventingand mitigating laboratory incidentsrequires effective management of a sys-tem of barriers that includes physical,operational, and organizational ele-ments. For example:

� T

Jo

he institution must determine whatfacilities and management resourcesare required to support specific re-search proposals (including the abil-ity to house new chemicals andassess additional hazards they createin the laboratory) and determinewhether such facilities are availablewhen such proposals are funded;

� L aboratory equipment with appro-

priate controls must be provided forthe experiments being conducted;

� S afety equipment must be identified,

provided, maintained, and inspectedto ensure that it will function asdesigned if it is needed (i.e. emergen-cy shut-offs, safety showers, eyewashes, etc.);

urnal of Chemical Health & Safety, May/J

� O

un

rganizations and individual labo-ratories must support safety educa-tion and training by establishingclear safety expectations throughpolicies and procedures and thenmaintaining oversight services thatidentify opportunities for improvingtraining;

� A ppropriate emergency response

and waste management servicesmust be provided for the laboratorywork being conducted, and

� C ontinuous monitoring and re-

sponse is required at all levels ofan organization to ensure adequateand effective barriers to prevent ormitigate laboratory incidents.

Compounding the challenge of effec-tive safety management is the increas-ingly interdisciplinary nature oflaboratory science. As biologists, physi-cists and engineers collaborate withchemists, the complexity of the hazardspresented increases correspondingly.Control strategies for chemical hazards,biological agents and physical dangerscan differ significantly and sometimescompete for attention and resources.Cross-disciplinary collaboration can re-sult in workers being involved in labo-ratory processes that they may not bewell educated in. For this reason, it isimportant to develop a safety commu-nication system that clearly highlightssignificant hazards while being easy touse, share, and modify as work changes.

It is also important to remember thatthe management of laboratory safetyhas the potential to affect people otherthan those physically conducting thework. The disruption of neighboringactivities on many campuses and thelegal impacts of the 2008 fatal fire atthe University of California, LosAngeles (UCLA) made it clear that lab-oratory incidents can have conse-quences impacting not just theprinciple investigators overseeing thework, but neighboring researchersand institutions as a whole in terms ofboth productivity and reputation.9,10

Even incidents that result in no injuriescan have serious financial conse-quences, such as recovery costs of over$1,000,000.11

These considerations mean that alarger network of stakeholders shouldbe included in developing safety tools.

e 2017

The bowtie approach described in thispaper presents an opportunity toimprove institutional understandingof laboratory risks by facilitating com-munication and management of theseissues among the wide variety of sta-keholders in academic laboratory re-search. Stakeholders includeuniversity presidents, senior adminis-trators, laboratory faculty and staff,environmental health and safety staff,and students.4 Such a diverse group ofstakeholders means that communica-tion tools may have to be redesignedwith different levels of detail to addressvarious questions from differentgroups. Fortunately, software forbuilding bowties is available to supportthe reuse of information developed forone set of stakeholders, thus commu-nication tools may easily be adaptedfor the needs of others.12,13

To address this daunting list ofneeds, ongoing communication amongthe various stakeholders at an academ-ic institution is necessary. A graphicalrepresentation of an institution’s safetybarriers and controls is likely to besignificantly more valuable to supportcommunication than a collection oftext-based policies, procedures, andchecklists – especially when commu-nicating with audiences who do nothave a background in the chemicalsciences or risk assessment.

THE ORIGIN OF BOWTIE DIAGRAMS

Using graphical imagery to describesafety systems has been shown to beeffective in supporting hazard commu-nication needs. In 2000 James Reasonpresented a popular model depictingthe progression of an incident througha series of leaky barriers.14

[6_TD$DIFF] This model,aptly referred to as the ‘‘Swiss cheesemodel’’, is presented schematically in[1_TD$DIFF]Figure 1. In this model the slices ofcheese represent ‘‘barriers’’ such asthose outlined above, while the holesrepresent barrier deficiencies in specif-ic elements in the system. These defi-ciencies can allow a threat to penetratethe system and result in an incident. Anincreased number of barriers withsmaller and fewer holes will lead to amore robust barrier system for prevent-ing incidents.

15

[(Figure_1)TD$FIG]

[1_TD$DIFF]Figure 1. James Reason’s Swiss Cheese model of accident causation.

A more sophisticated graphical toolknown as the ‘‘Bowtie Diagram’’ alsoexists. Bowties garner their name fromtheir shape (see [1_TD$DIFF]Figure 2) and depictthe relationships between hazards andbarriers in a holistic way. The firstappearance of bowtie diagrams hasbeen attributed to lectures on HazardAnalysis given at The University ofQueensland, Australia in 1979, butthe exact origin of bowtie diagrams isnot clear.15

[7_TD$DIFF] Their use was pioneeredlargely by the oil and gas industry, andnow can also be found in the aviation,mining, maritime, chemical and healthcare industries.

After hazards have been identified,the bowtie tool can be used as a risk

[(Figure_2)TD$FIG]

[1_TD$DIFF]Figure 2. Generic bowtie diagram depictinprogress to a variety of negative consequen

16

assessment aid and communicationdevice to depict the number and typeof barriers (e.g., physical, organization-al, or operational) that must fail inorder for an incident to occur. Whilethis model has been used in large-scaleindustrial settings, we believe the con-cept can be adapted to the laboratorysetting to create a useful communica-tion tool for this challenging manage-ment environment.

Because best practices in developingbowtie diagrams are still evolving,there are a variety of terms and con-cepts that need to be defined in orderto develop a useful bowtie diagram.The precise use of these terms andconcepts will vary depending on the

g multiple threats that can escalate to a loces.

Journal of Che

expertise of the people involved in de-veloping the diagram. However, themain goal for developing a bowtie dia-gram is to aid in communication andassessment of the fundamentals of thesafety system. The following sectiondescribes the basic process of develop-ing a bowtie.

� H

ss

m

azard – As illustrated in [1_TD$DIFF]Figure 2,at the top of a bowtie diagram is ahazard of concern, i.e. somethingthat has a potential to cause damageor loss if it is not properly controlled.Hazards are dangerous intrinsicproperties of the materials or pro-cess that cannot be eliminated. In alaboratory setting, these hazardscould be described as ‘‘explosive sol-id,’’ ‘‘flammable liquid,’’ or ‘‘corro-sive chemical’’ amongst others.Safety Data Sheets that conform tothe Globally Harmonized Systemprovide a general approach for iden-tifying chemical hazards associatedwith a process.

� T op Event – The center of the bowtie

is the ‘Top Event’ which identifies thepoint in time when control of a spe-cific hazard is lost, and this loss couldresult in specific forms of harm.

� T hreat– The threats listed on the left

side of the bowtie are events that canbegin the chain of action leadingtoward the top event.

� C ontrol– Preventive barriers, shown

between a threat and the top event,are designed to either prevent the

of control of a hazard, and in turn,

ical Health & Safety, May/June 2017

Jo

threat from occurring or stop theescalation of a threat to the pointwhere it becomes involved in a topevent. If a top event occurs, then themitigation barriers on the right sideof the bow tie are intended to eitherstop or minimize the severity of un-wanted consequences.

A [8_TD$DIFF]LABORATORY EXAMPLE

In March 2016, the Division of Chem-ical Health & Safety (DCHAS) pre-sented an interactive symposium atthe American Chemical Society(ACS) national meeting. The sympo-sium was held to assess the value of thebowtie methodology in a laboratorysetting.16 The example used in the ac-tivity was based on the 2011 CSB casestudy of a laboratory incident at TexasTech University (TTU).1

To construct the bowtie, participantswere asked to identify its parts in ac-cordance with widely accepted bestpractice in the oil and gas industry inthe following order17,18

[9_TD$DIFF]:

1. H

u

azard/Top Event

2. A ll Consequences 3. A ll Threats 4. P reventive Barriers 5. M itigation Barriers

Initially a variety of possible top

events were identified, but the hazardwas generally agreed upon by all parti-cipants as ‘‘energetic material’’ Possibil-ities for the top event discussed were:

� I

ntentional scale-up � E xplosion/detonation � E xceed safety critical limit (In this

case, a safety critical limit is the min-imum amount of material that couldcause permanent bodily injury if det-onated)

[1_TD$DIFF]Figure 3. Initial bowtie diagram showing hazard and top event.

The group agreed to use ‘‘exceedsafety critical limit’’ as the top eventfor two reasons. First, identifying thescale-up as ‘‘intentional’’ limits the ap-plicability of the bowtie. For example,prior to the 2011 incident, anotherTTU student unintentionally scaled-up the synthesis of another energeticmaterial.1 While the barriers to prevent

rnal of Chemical Health & Safety, May/J

unintentional or intentional scale-upsmay be different, once safety criticalamounts are exceeded, the barriers toprevent or mitigate consequences of adetonation are the same. Therefore,choosing ‘‘exceed safety critical limit’’allows the bowtie to cover multiplethreat scenarios for a single hazard.

Secondly, choosing ‘‘exceed safetycritical limit’’ as opposed to ‘‘explo-sion/detonation’’ puts the risk man-agement focus on a point in timewhen the laboratory workers can stillrespond and avoid a detonation alto-gether. Figure 3 presents the initialbowtie diagram with the group-decid-ed hazard and top event.

Several potential consequenceswere suggested:

� I

un

njury/fatality due to detonation

� P roperty damage due to detonation � R eputation damage due to detona-

tion

� L oss of business/productivity/grant

funding due to detonation

� R egulatory/external review

Potential consequences extend be-

yond the individuals and laboratoryinvolved and can affect multipledepartments in the university, as ap-parent from the above list. Althoughproperty damage and regulatory/exter-nal review would be valid conse-quences, due to the time constraintsthe workshop leaders focused on threeconsequences listed in the evolvingbowtie diagram shown in [1_TD$DIFF]Figure 4.

Identifying potential threats was themost challenging part of constructing a[(Figure_3)TD$FIG]

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bowtie for the group. The participantsinitially listed the following as poten-tial threats that could lead to exceedingsafety critical limits (top event):

� N

o written procedures � N o personal protective equipment

(PPE) policy

� U ntrained laboratory workers � I nadequate supervision � L ack of communication

Listing failed or degraded barriers

(such as those listed in the bulletsabove) as threats is a common mistakein bowtie development. In response,the workshop leaders guided the grouptoward [10_TD$DIFF]threats describing an initiatingevent that if left unchecked could es-calate to a laboratory worker exceed-ing a safety critical amount of energeticcompound. After this instruction, thegroup identified three key threats:

� I

ntentional synthesis scale-up of en-ergetic material � I nadvertent synthesis scale-up � U nauthorized (criminal) activities

[1_TD$DIFF]Figure 5 shows the developing bow-

tie diagram which now includes thegroup-identified threats that couldlead to the top event (exceeding thesafety critical limit). Finally, the groupdiscussed and listed the various pre-ventive and mitigative barriers. Theresulting bowtie diagram based on thisworkshop activity is shown in [1_TD$DIFF]Figure 6.The bowtie diagrams in this manu-script were prepared using BowTieXPsoftware.13

[1_TD$DIFF]

17

[(Figure_4)TD$FIG]

[1_TD$DIFF]Figure 4. The evolving bowtie diagram showing group suggested consequences.[(Figure_5)TD$FIG]

[1_TD$DIFF]Figure 5. Bowtie diagram showing the threats agreed upon after group leaderguidance.

BOWTIE [11_TD$DIFF]DEVELOPMENTPRECAUTIONS

A potential pitfall of the bowtieapproach is that users over-identify[(Figure_6)TD$FIG]

[1_TD$DIFF]Figure 6. Bowtie diagram for the detonatio

18

barriers and generate a false sense ofsafety since more barriers may beexpected to reduce associated risks.For example, the bowtie in [1_TD$DIFF]Figure 6 lists‘‘activating emergency alarms and

n of energetic material in a laboratory settin

Journal of Che

response’’ as a barrier. To ensure thisbarrier functions, a laboratory workerneeds training to know where the alarmis located, how to activate it, and how torespond once it is activated. Further-more, it is imperative the alarm is prop-erly maintained so that it will functionwhen activated. Ultimately, the alarmand associated training and mainte-nance actually represent a single barriersystem, without which there is no as-surance the barrier will function at all.When an ‘‘alarm’’ is listed as a barrier, itshould be with the understanding thatthere is safety management system sup-porting it that includes training andmaintenance. Without this, there are‘‘holes’’ in the barrier analogous to theSwiss cheese model.14

Management systems are the formalprocesses where management (e.g.,principal investigator, departmentchair, etc.) commits to policies or pro-cedures that support safety, implementsthe policies and procedures, monitorstheir performance, and implements ap-propriate corrective actions when nec-essary.19 Monitoring performance andimplementingcorrectiveactions shouldbe a continual process which results inimproving the management of risks andsafety throughout the lifetime of a re-search program. This is true whetherthe barrier is physical in nature likethe alarm example (technical), or anorganizational policy (cultural). Ulti-mately, a piece of paper is not a barrier– risk assessment and management isan active process. It is the actual workconducted under the policy or proce-dure that creates the barrier. If a policyor procedure is not consistently moni-tored and reinforced, the operational

g.

mical Health & Safety, May/June 2017

barrier can degrade and fail. In the lab-oratory setting, operational barriers arenecessary and heavily relied upon. Thisis illustrated on the bowtie in Figure 6where the only barrier listed to prevent‘‘intentional scale-up’’ is a policy not tosynthesize amounts greater than thesafety critical limit.

USING [12_TD$DIFF]BOWTIES TO FACILITATERISK CONVERSATIONS

Bowties are part art and part science.There is no single ‘‘right’’ way to createa bowtie. As long as a group developingthe bowtie leverages in-house exper-tise and identifies their most significanthazards and the needed controls, thenthe bowtie can be a useful tool tofacilitate risk conversations amongstnumerous stakeholders. For example:

� A

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s the bowtie in [1_TD$DIFF]Figure 6 indicates,mitigating potential consequencesmay require resources outside ofthe chemistry department such apublic relations department to han-dle media attention.

� B owties help depict whether a risk

management approach is focused onpreventing dangerous situations ormitigating them after they have oc-curred. For example a fire hazardwill not be controlled by PPE andso a well-developed bowtie wouldhighlight that PPE is only helpfulin mitigating potential burn injuries,not in preventing the hazardousconditions that can lead to a firefrom occurring in the first place.

� A graduate student or other labora-

tory worker initiating a procedurecan review an existing bowtie as areminder of the critical barriers toensure they are in place and func-tioning before initiating work.

� D uring a laboratory safety audit, an

inspector without expert knowledgeon a process and its hazards couldreview a bowtie and ask about thesafety management systems con-nected to the barriers indicated onthe diagram. This can include talkingwith the individuals responsible formonitoring and maintaining differ-ent barriers.

� I ncidents and serious consequences

occur when barriers fail. Bowties

urnal of Chemical Health & Safety, May/Jun

can be the starting point of an acci-dent investigation to determine howand why the barriers had failed, wereinadequate, or were bypassed.

CONCLUSION

Bowtie methodology could prove use-ful in aiding universities to furtherimprove how they manage their labo-ratory risks. It provides a structuredapproach to identifying key safety bar-riers and controls so their strengthsand conditions can be monitored moreeffectively to prevent barrier degrada-tion. These are the types of improve-ments necessary to go beyond currentlaboratory safety practices and achievea proactive safety culture.

Bowties facilitate effective risk con-versations by providing a visual aid toprompt conversation rather than rely-ing on sometimes cumbersome text-based policies, procedures and check-lists. Presenting information in multi-ple formats supports learning by adiverse group of workers whose learn-ing styles, languages skills and techni-cal expertise can be expected to varysignificantly. Universities can also ap-ply this technique as part of their audit-ing process to help identify wherebarriers may need to be strengthenedor added, and this can drive the crea-tion of effective actions toward [13_TD$DIFF]furtherrisk reduction efforts. Ultimately, bow-ties provide a good roadmap for asses-sing the quality and number of riskcontrols to prevent serious laboratoryincidents and facilitate the identifica-tion of clear actions to improve con-trols and advance the ‘‘cultural’’ side ofsafety management.

REFERENCES1. U.S. Chemical Safety and Hazard In-

vestigation Board (CSB), 2011. TexasTech University Laboratory Explosion:Lubbock, TX, 2010, January 7, ReportNo. 2010-05-I-TX. http://www.csb.gov/assets/1/19/CSB_Study_TTU_.pdf[accessed 06.09.2016].

2. Kemsley, J. Researcher Dies After LabFire: UCLA research assistant burnedin incident with tert-butyl lithium.Chem. Eng. News, 2009 Web Date:January 22, http://cen.acs.org/articles/87/web/2009/01/Researcher-Dies-Lab-Fire.html [accessed 06.09.2016].

e 2017

3. Kemsley, J. Spark from pressure gaugecaused University of Hawaii explosion,fire department says. Chem. Eng. News,2016 Web Date: April 19, http://cen.acs.org/articles/94/web/2016/04/Spark-pressure-gauge-caused-University.html [accessed 28.04.2016].

4. The Association of Public and Land-grant Universities, A Guide to Imple-menting a Safety Culture in OurUniversities. http://www.aplu.org/library/

safety-culture/file [accessed 31.08.2016].

5. National Research Council. PrudentPractices in the Laboratory: Handlingand Management of Chemical Ha-zards, Updated Version;; National Aca-demies Press: Washington, DC, 2011,doi:10. 17226/12654.

6. American Chemical Society. Identify-ing and Evaluating Hazards in ResearchLaboratories. 2015. http://www. acs.org/hazardassessment [accessed 06.09.2016].

7. Occupational Exposure to HazardousChemicals in Laboratories, Definitions,29CFR1910.1450(b). https://www.osha.

gov/pls/oshaweb/owadisp.show_document?

p_table=STANDARDS&p_id=10106 [acces-

sed 06.09.2016].

8. National Research Council. SafeScience: Promoting a Culture of Safetyin Academic Chemical Research; Na-tional Academies Press: Washington,DC, 2014, doi:10.17226/18706.

9. Torrice, M.; Kemsley, J. Patrick Harranand L.A. District Attorney Reach DealIn Sheri Sangji Case. Chem. Eng. News,2014 Web Date: June 25, http://cen.acs.org/articles/92/web/2014/06/Patrick-Harran-L-District-Attorney0.html [accessed 31.08.2016].

10. Kemsley, J. AAAS rescinds election ofPatrick Harran as a fellow. The SafetyZone by Chem. Eng. News, 2015Posted on December 23, http://cenblog.org/the-safety-zone/2015/12/aaas-rescinds-election-of-patrick-harran-as-a-fellow/ [accessed 06.09.2016].

11. Bierman, P. The University of Ver-mont, Cosmogenic Nuclide Laboratoryand Geomorphology Research Group,Memorial Day 2007, was not such agood day http://www.uvm.edu/cosmolab/

?Page=fire.html&SM=about_sub_menu.

html. [accessed 06.09.2016].

12. BowTie Pro, Home Page, http://

bowtiepro.com [accessed 04.09.2016].

13. Software Products, CGE Risk Manage-ment Solutions, http://www.cgerisk.com/

software [accessed 04.09.2016].

14. Reason, J. Human error: models andmanagement. Brit. Med. J. 2000,320(7237), 768–770.

19

15. The history of Bowtie, CGE Risk Man-agement Solutions, http://www.cgerisk.

com/knowledge-base/risk-assessment/

the-bowtie-methodology [accessed 04.09.

2016].

16. Mulcahy, M.; Boylan, C. Introductionto Bowtie Methodology for a Labora-tory Setting. Presented at the 251st

American Chemical Society NationalMeeting & Exposition. Boston, MA,March 15th, 2016.

20

17. A Barrier Focused Approach: How toGet Started with Process Safety, Vol. 2(Draft), ENFORM. The Safety Associa-tion for Canada’s Upstream Oil andGas Industry, 2016 (http://www.enform.ca/files/pdf/process_safety/Barrier_Focused_Approach_How_to_get_started_draft.pdf [accessed 10.06.2016].

18. Project 237: Guidelines for BarrierRisk Management (Bow Tie Analysis),

Journal of Che

http://www.aiche.org/ccps/community/

projects/project-237-guidelines-barrier-

risk-management-bow-tie-analysis [acces-

sed 04.09.2016].

19. ANSI/AIHA/ASSE Z10 Committee.Occupational Health and Safety Man-ag. Syst. 2012 viii.

mical Health & Safety, May/June 2017