Barrier analysis identifies and analyzes barriers that are associated with accidents. It considers potential hazards, targets, and assesses the adequacy of barriers that should have prevented or mitigated the accident. There are several types of barrier analysis including hazard-barrier-target analysis, energy trace and barrier analysis, and barrier and control analysis. Barrier analysis uses a chart and worksheet to graphically explain accidents and analyze barriers that could be corrected or added to prevent future accidents.

1. CHAPTER9
Barrier Analysis
0 ne of the most important purposes of a safety program is to
identify
hazards and establish barriers that will keep hazards from
coming in contact
11~th workers. Barrier analysis is the identification and
analysis of barriers that
are associated with accidents.
There are several types of barrier analysis. Most accident
investigators
use hazard-barrier-target (HBT) analysis, which considers
potential hazards and
potential targets and assesses the adequacy of barriers or other
safeguards
that should have prevented or mitigated the accident (Spear
2002). Energy trace
0nd banier analysis (ETBA) and barrier and control analysis
(BCA) are useful for
preventive analysis. ETBA traces the energy flow or energy
path throughout
the system and analyzes barriers for adequacy (Stephenson 1991
). BCA locates
hazards · In a system and focuses on how to control them.
AboutB · An . arner alys1s
Barrier anal · c • T ysis 1or accident investigations can be
traced back to the MOR
system creat db B" hni w e Y ill Johnson for the Department of

2. Energy. The tee que
as develop d · c
I
e to look at an unwanted energy flow and determine what
barners
ou d contain th . . reali e flow. Safety professionals and
accident investigators soon
~~thMo . anal e RT system and barrier analysis could be used
for reactive
Yses such · . 985) as accident Investigations with excellent
results (SSDC 1 ·
93
Part lJI· A , 1z· IT.
· na!Y ca ech11iq11es
94
Other types of barrier analyses and work h
1980 s eets wer . s and were called by different names HB1' e
used In the 1970,
t h · c · . · anaJys1s1sth b . 'lid ec nique ,or accident
mvestigations It c b e an:ier,n,1,...
. an e used for s· - ,,. well as complex accidents to determine
how th h linple accid,n~
e azard reached the
The Barrier Analysis Approach
Two products of barrier analysis-a chart and an analysis

3. Worksheet- arc
together to graphically explain accidents and analyze the
barriers that
0
,:!
be corrected or added. The chart illustrates hazards, barriers,
and tatgeij. 11,,
concept of the chart is simple: the investigator identifies a
hazard and,~
and then determines the barriers that could keep the hazard from
reaching
the target (see Exhibit 9.1). The analysis worksheet is used to
describe th,
purpose and evaluate the performance of each barrier.
Exhibit 9.1Afioicj
BARRIER ANALY$1S.,GRAPflW --c.
HAZARDS
)tr
B
A
R
R
I
E
R
. Analysis Process The Barner
9. Banier A na!ysis Chapter ·

4. . Chart h ard and the target. In alysts · fy the az th
Barrier Ml . al sis is to identl the hazard would be . e
fbe t step in baroer : e:ployee, for exampl~he next step is to
identify .
1],e firs fan electrocute uld be the employee: fi l, d barriers that
111ere
the case o d the target wo f barriers-bamers that a, e ,
dectricil)' an ee categories o . e Exhibit 9 .2). .
brainstorrn thr that did not exist (se I d only if all barners or d
bamers . be comp ete
not 1111d, an f barrier analysis can . . g is a good way to · "part
o d d Brainstonru.n Th "analysis . are inclu e .
e .th the accident Exhibit 9.3).
associated w1 . e list of barriers (see . e the types
·e-a comprehens1v . t investigators categonz
mak n safety professionals and acc1~:nhard (engineered) barrie
rs and _soft
Ma y . other way as well- . 1997) Engineered barriers f bamers
10 an Safety Society · .
o( d ·rustrative) barriers (Sys tem hi guards and protective
eqU1pment.
a rm . uch as mac ne d work
are physical res tram ts s olicies and procedures-approve . .
Administrative bamers are P . ntrol (SSDC 1985). Exhibit 9.4
· · nd superv1sory co d
methods, job trauung, a b . that would have prevente an f b ·
Any arner .
lists these types o arners. _ b . alysis. Categorizing barriers b .
ated into arner an f accident must e mcorpor the brainstormed
list o as "hard" and "soft" is a good way to structure

5. barriers.
Exhibit 9.2
C BARRIE( CATEGORIES
1. Barriers thatfalled The barrier was in place and operational at
the time
of the accident, but it failed to prevent the accident. 2
• Barriers that were The barrier was available, but workers
chose not to not used use it.
;--:--__~-:----------------:-----:-:----
3· Barriers that did The barrier did not exist at the time of the
accident. -------------
95
96
Part Ill· A · 11a!,tica/ T. . ech111q11es
Exhibit 9.3
Barriers that failed
1.
2.
3.
Brainstorm the barriers tho
used that failed and record ~:ere
here. em

6. Barriers that were not used
1.
Note: The key to h.
stormingsess· t. 1sbrain.
Ii
10n1stot ndal/ofther. .1 'Y to or nonexistent ab1 e~ unused,
n amers Do
ot be co~cerned if yo~ a,
not cena,n which cat e
they belong in. ,gory
2.
3.
Brainstorm the barriers that were
not used and record them here.
Note: The difference between
;:==:--=;:_-::-::-;:;-:-----:---------_J these two categories is that
Barriers that did not exist "barrierrnotused'were
1.
2.
3.
Brainstorm the barriers that did not
exist and record them here.
available but were not used·

7. "barriers that did not exist''
were not available.
The short example on the next page demonstrates the barrier
ana!Jsis
approach.
A worker was mowing a lawn when a rock flew out from
beneath
the mower and hit another worker who was walking to her car.
In this example, a failed barrier is the plastic rock guard
under=•
(
oineered barrier). A barrier not 11sed ,s the comp y
m ower an en,,-- · when
procedure that states that workers. should stop :~)~artier
_ "-'~ b (an adrrunistrattve barn ·
people are wauui,g near Y dminisrracive bar-
. • h kli t/walkaround (an a d
that did not exist 1s a c ec s . h k for rocks an b f, owing to c ec
rier) the worker should use e ore m d and equipment
d the ground and check that all guar s
h azar s on . . d O eracing,
are in place, in good condiaon, an p . invescig:icio~
. d es of barriers in ever)' A ,ou caJl
you will not find all ca tegones an typ e es and categones. s J
. . rirical to brainstorm all of th typ
However, tt is c

8. Chapter 9: Barrier A11afysis
ADMINISTRATIVE
ENGINEERED 1. Procedures s
I. Machine guards
H 2. personal protective 2. Training 0
equipment 3. Supervision
A J. Fall protection 4. communication F
R 4. Interlocks s. Work planning T
D
s. Electrical systems 6. Standards and
6. Safety valves
regulations
., in the lawn mower example, there were at least three ways
this accident
could have been prevented. A barrier analysis summary chart is
s h own in
Exhibi1 9.5. This type of chart is useful not only for fact
finding and analysis,
buralsofor identifyingcorrective actions. Use the chart and the
last column
of rheanalisis fonn to prevent recurrence of an accident.
Exhibit 9.5
HAZARD---- Flying rock
t

9. {
Rockguard
BARRIERS
Procedure
Checklist/walkaround
t TARGET--
Worker
Note: One of the key 1
uses for this type of
chart is to develop
corrective actions.
If any of these barriers
had worked, the
hazard (the flying
rock) would nat have
come into contact
with the worker and
the accident would
not have occurred.
97
Part Ill: A nafytiral Ttchniques
98
After all barriers are brainstormed cate . .
• gonzmg them way that benefits the organization It is all can be

10. handled ·
. . usu y useful to tn any barners from administrative barriers
f;or . d separate enoi"
ease In evelo i ct'•~ett-d to address o r alleviate the problems E
n,,;n d b _P ng corrective >cti~.
. . e,· eere arners that f . ·~ d esign problems that can be
corrected by en,,; ad are usu,,c
department, w hile adnurustrative barriers that fail ntenan« . . .
e,·neers or the mai ---.,
are usually man system p roblem s that must be corrected by
management. agcrn,n,
The Barrier Analysis Worksheet
A worksheet is u sed to analyze the performance of the barriers.
Exhib1t
9
_
6 is a sample worksheet.
• Column 1: List the barriers, as illustrated in Exhibit 9.6. They
can i,
lis ted b y category (failed, not used, did not exist) or type
(engineered or
administrative) .
Column 2: D escribe the intended function of each barrier. In
the 1,-.
m ower example, the guard is an engineered barrier intended to
keep items
from flying out om . . . . . ull . fr under the mower deck. The
procedure of stopputg

11. . alkin. b is an administraave bamer that ,o when someone 1s w
g near Y
have prevented a rock fro m hitting someone. . .
formance of the barrier. Each bamer Is • Column 3: Evalua te
the per hi a target. The lawn mowa
hazard from reac ng
supposed to prevent a . hi h allowed the rock to fly out
guard failed because it was defecnve, w c
. S mmary Chart . ol
Barrier Analysis u . list of the bacrierS assooat
. chart is slITiply a
I
d workshc<L
A b arrier analysis summary b generated from the compete
anagem01t
. d The list can e . port or m with the ace, ent. di . to an accident
re . ....,ding th<
lJent ad uon · coons '•o-This chart is an exce d develop
correcuve a
also be use to briefing, and it can
use of barriers.
Chapter 9: Banier Analysis
B~RRIER
~barriers.

12. BARRIER ANALYSIS FORM
PURPOSE OF
BARRIER
PERFORMANCE
OF BARRIER
,.
I.
2.
2. _______ _
Record the purpose of
each barrier.
Analyze the
performance of each
barrier. Try to focus on
the effect of the barrier
on the accident or
accident sequence.
Example Scenario
funieranalysis analyzes barriers that failed, were not used, or
did not exist.
)1011 oi the barriers in the forklift-ladder scenario either failed-
supervisor
1
runing-or were not used-scheduling , a safety review,
procedures ,

13. b1mcades, and communication. The barrier analys is form and
barrier analysis
'utnmary chart are illustcated in Exhibit 9.7 and Exhibit 9.8
respectively . 8
llritt,naJ},is demonstrates that when this accident occurred,
many barriers
""ltd
th
at could have prevented the accident, but they were not used.
99
Pan///: A
'
1abtu-a/ T echmqurs
Exhibit 9.7
BARRIER ANAL Ys1s OF
BARRIER PU
1. Scheduling and
safety review
2. Job procedures
3. Barricade
4 . Communication
s. Supervisor training

14. --
BARRIER PERFORMA,.CE
OF BARRIER 1- Toevatuatealljobs
and incorporate safety 1. This barn er fa iled
measures to ensure the because a safety
safety of Workers. review Was not
performed for thls
task; perforrning it
would have prornpted
the worker to use the
correct procedure.
2. To ensure that all
personnel who
perform tasks are
trained and use the
same sequence.
2. This barrier fa iled
because upper
management did not
enforce procedures
and the new supervisor
did not use the proper
procedure.
3. To wa rn forklift drivers 3. This barrier fa iled
that work is being
done in the aisles.
4. To ensure that all
information is shared

15. between supervisors
and employees.
s. To ensure that
supervisors are
adequately trained
on management
responsibilities.
---
because the
warehouse supervisor
failed to barricade the
aisle.
4. This barrier failed
because there was no
communication about
the job between the
supervisors.
5. This barrier failed
because the new
supel'l'isor did not
adequately perfo~
his supervisory doues.
The culture from op~
management seems t?
be "Get the job done. --
CbrlfJ/er 9: Bt1m 'er Ana(J•si.s
OF EXAIIIPLE SCENARIO
£.b>"'' 9.S ALYSIS su111111ARY

16. RRIERAN
8.1 Hit by forklift/
~,uARD --Fall tram height
!
{
Review
Procedure
BARRIERS Bamcade
commurncat1on
Super,,sr uam<ng
TARGET ----Worker
Summary
.:hoogh mmy types of barrier analys is exist, all see k to
accomplis h the
agotl-acc1dent analysis. The hazard -barrier-targe t (HB1) type
of barrier
~1m can be used on all accidents regardless of s ize . It is a
very e fficient
mro wlp:e smaller, first-aid-type accidents.
61Ccideminvestigations, barriers are either engineered or
adminis trative .
i:ry can be 1ewcd as barriers that failed, were no t used, o r did
not exis t.
Si.ma an1lys1s hdps an investigator to identify barrie rs, d
escribe the ir

17. f .. 7JS(, and analrze their performance. Afrc r t!Us analys is is
per fo rmed ,
:~ be used to develop corrective actions. (Please see the
Appendix fo r a
Barner Analysis fonn.)
101
102
Part Ifl: A 11a!Jtical Tech11iques
REVIEW QUESTIONS
1. What does barrier analysis try to accomplish?
2. How can barrier analysis be used to prevent accidents?
3. What three categories should be brainstormed during barrier
analysis?
4. List two types of engineered barriers and two types of
administrative barri ers.
s. How can a barrier analysis summary be used to recommend
corrective
actions?
6. Many barriers are used when mowing, edging, and weed
trimming. List
all of the barriers that keep you from receiving an injury when
doing yard
work. Also, list any additional barriers that could be added or
used that could

18. prevent injuries from yard work.
CHAPTERS
Change Analysis
A change of some sort is a major factor in most accidents.
Although
change is a necessary component of progress, it can also be
catastrophic.
Change can be planned, anticipated, or desired; it can also be
unintentional
or unwanted. Change analysis is a technique for analyzing the
changes that
led up to an accident. It can be combined with other techniques
or used
independently.
Change analysis can be used both reactively and proactively.
When it is used
reactively, the investigator looks back at the events that led up
to the accident
and determines the unintentional or unwanted changes that may
have caused
it. v'hat was different about how the process was performed
this time that
caused the accident to happen? When it is used proactively,
safety professionals
develop scenarios that introduce a planned, anticipated, or
desired change into
a 5Ystem and use change analysis techniques to identify
potential hazards or
accident situations that could arise because of the change.

19. Change analysis
can also be used to review processes or to identify the potential
effects of
changes before implementing a new procedure or process
(Stephenson 1991)
(Spear 2002). Many safety professionals use a modified change
analysis process
10 comp[ ·th I · t i Y w1 the Process Safety Management regu
atory reqw.remen s or
managem f enc o change.
83
Part Ill: ,-l11aJy11· I r, h . ra re mqurs
84
About Change Anal . ys1s
The technique of change analysis was first
1981) and was perfected by Chari K used before World W
U.S. Air Force in the 1950s Billjesh epner and Benjarnu,y
aru(Po,..
M . o nson I rego, I ,,
anagemem Oversight and Risk T a so used this tech . o, II,
D ree (MOR1) lllqo, .
epanment of Energy. When using it th . . system deveJo""d lo II,
f 1 . , e lnvesngator r- fo1 ,, o events eading up to an accide .th .
. compares th '"' nt w1 a sunilar . e seo., ....
find the causes of the accident non-acc1den, sequ ,~..,
. ~-

20. Although change analysis can be used with .
it is most useful for accidents that h ~ny accident investigatio
appen while routine
performed. For first-aid incidents, near misses and .d tasks are~
. I , aca ems that
sunp e tasks, change analysis may be sufficient on it
oceurdoriog
h d . will . s own to detennin .,,1... appene ; It provide enough
information to deterrnin h ' • ..,
the sequence from developing again. e ow to P•ev~,
For more complex accidents, change analysis must be
. . . _ structured ar.a
detailed. It 1s not enough for the rnvesagator to simply ask,
"What chang.i
to cause the usual sequence of events to turn into an accident
sequence?"
Every event that changed, including management systems
events, mus, I,
analyzed in detail, and frequently other analysis methods must
be osed i,
addition to change analysis.
The Change Analysis Approach
The approach of change analysis is to compare an accident
situation "
sequence with a similar accident-free situation or sequence. The
basic ~
analysis sequence is illustrated in Exhibit 8.1 and a summary of
compll!lOO
methods is illustrated in Exhibit 8.2.

21. Types of Accident-Free Situations
f . tion or sequence to
It is critical to find a directly related accident- ree smia . be
us,d:
f s1tuauons can compare with the accident situation. Three
types o
Chapter 8: Change Analysis
Analyze
Procedure as It Is Usually Performed 11,eSame .
. . . able to compare the accident sequence with the ideally the
,nvesogator IS th
' d it was performed accident-free-last week, last mon , same
proce ure as . . .
S. accident did not occur dunng that struaaon, what was
orlmyear. mcean . .
different in the sequence this time that may have comnbuted to
the acadent.
A Description of the Job as It ls Supposed to Be Performed
Comparing the accident sequence to a written description of
how a task is
supposed to be performed makes change analysis simple for the
investigator.
This process is also called Codes, Standards, and Regulations
(CSR), Procedure
Design Criteria Analysis, or Procedure Adherence Analysis. The
investigator
compares the accident sequence to the procedure, standard, or
regulation

22. ind discovers where change has occurred. One problem with
comparing the
accident sequence to a task description sequence is that the
worker involved in
ihe accident might not actually have changed the usual
procedure. It is possible
tluiworkers have neverperfonned the job as it is described by
the standard or
Procedure If this · th th • d . · " e case, en It was not a change
but a dijfmnce from the
ocnbed procedure that caused the accident.
85
Part I I I: Ana/ytiral Tuhniqun
86
Exhibit 8.2
1. ~n "'accident-free" Ho . :
situation w the Job was perfor last year with no accid med last
week, last rno
2. Plant procedures ents. ntti.or
How the task was supposed t
according to company policy~ be~
3• An "'ideal" situation How the job would be rf
circumstances. pe ormed unde~
A Description of the Job as It Should Be P rli
This sounds very much like the co . . e ormed . mpanson 111 the
•

23. ts s~btly different. In this kind of comparison, the ~r::~us
Patagnph, bu111
accident sequence events not with written standards :ugat.or
compucs die
of the way the task would be performed und .d I u_t with a
description hi h er I ea c1rcumstao With
t s met od. the investigator is not comparing changes but di;t !
between the accident sequence and the ideal sequence, since
the:;:
probably never been performed in the ideal way. lf the
investigator finds 1
be~er way to perform the procedure, it can be recommended as
a correCU·r
acaon.
Making Thorough Comparisons
Js you perform change analysis, you must compare all events
and conditioos
involved in the accident with corresponding events and
conditions in tht
accident- free scenario. Ask the following guestions about each
e·ent
u:a.t involved? lf:i"hat happened? IV'ht11 did ii happm? When
did it buppui? H,, ,,;
it happen? Analyze each set of events and conditions and ask
what changes
may have occurred: l s the time or place different? Are the
people UJ'oh-c-d
different? On a managerial level, was it managed, controlled,
reviewed, ci
implemented differently? (DOE 1999.) After you have made'
tho...,gh
comparison find the differences between the two sequences. In
most
situations, they are guite obvious. Finally, determine how th:u
differtllct

24. caused the accident.
Ch(Jpter 8: C/J(Jflge A11(J!Jf1S
. I w demonstrates the chwge analys is approach.
1be short e,xamplc be o
fi
h'ng every day for cwenty years, and every day he
b had gone is l . Bo '
1
aich fish for his lunch and dinner. One day, he
dbeenabetoC had
001
catch any fish, and he wondered why. He compared tl1e
ful d ,
10
all of the previous successful days and found
unsuccess 3} . • th:it he had used the same fishing hole and the
s~e hook size, and
had fished
31
the same time of day. TI1e o nly difference was chat
he h:.1d used different bait on the unsuccess ful day, so he
reasoned
that using different bait was the cause of his failure to catch
fish.

25. :cadent in,·escig.itions will never be this easy to analyze, o f
course, and
th~ uu]ysis does not stop with finding that different bait was the
reason for
fishing f:ulu re. The next steps are lO learn why Bob decided to
change his
b
1
nand why the new bait didn't seem to attract fi sh. ln change
analysis, you
must find out al/of the changes that occurred and analyze how
they affected
the outcome.
Change Analysis Procedures
(lunge analysis is performed r I on a iour-co umn worksheet
(see Exhibit 8.3) .
• Column 1: Write the accident sequence.
: ~:umn 2: Xhite the events of a comparable accident-free
se9uencc
o umn 3: Note the differences or cha b . l and column 2. , nges
etween the events in column
, Column 4: Analyze the djfferenc .
how they affected the outcome. es or changes In column 3 and
detem1ine
Example Scenario
tltn perfomun ch
<ornpa g ange analysis , re to the accid , •) ou must find an
accid f
is a non- . ent se9uencc. Alth I ent- ree SC<...juence co

26. recurring task that has no sp~u~f,1 o u.r _forklift -and-ladder
scenario
ec1 ic wri tte n des . . c n ptton, there are
87
Part Ill · A · na!Jtica/ T. h . ec. 111q11es
88
Exhibit 8.3
ACCIDENT
SEQUENCE MP
~---.c.:c::.::. __ ___:S~E~Q~U~E~NC~E~
1. 1. DIFFERENCE
ANALYSIS 2.----i:__ __ _!.:__1.
========~2. ======2~~-====-+--
Describe
the accident
sequence.
Describe a
comparable
sequence from
an accident-free
situation.

27. Identify the
differences
between
the accident
sequence and
the comparison
sequence for
each step.
Analyzet;;-
differences and
describe how
they affected
the accident
procedures for using ladders and working in warehouse aisles,
and changing
light bulbs is similar to installing signs, so that procedure was
used as the
comparison sequence. Exhibit 8.4 lists only the events in the
accident sequence
that are different from those in the comparison sequence. After
the firstthrt<
columns are filled in, analyze differences between the accident
sequence and
the comparison sequence that could be significant to the
accident. The fourth . . fi . t on theacadenc
column lists several differences that had a s1gru 1cant unpac
1s0F EXAMPL
ACCIDENT

28. sEQUENCE
t 1. All jobs go
1. n,isjobdid no through a safety
obiain a safety and scheduling
revieW, review. -- . 2_ The warehouse 2. Maintenance
supervisor per· workers perform
formed the task. maintenance
tasks.
DIFFERENCE
1. No safety or
scheduling
review was
performed.
2. The proper
personnel did
not perform the
job.
3. No communi-
cation was
made to
3. Communication 3. The work was
the night
warehouse
supervisor.
4. No rows were
barricaded.

29. about work will not communi-
go through the cated to
supervisors. the night
supervisor.
4. All aisles and
ends of rows are
barricaded off.
4. Rows were not
barricaded.
Chapter 8: Change A11afys1s
ANALYSIS
1. A safety
review was not
conducted; it
would have
initiated
the proper
procedures.
2. The workers
who are familiar
with the
procedures did
not perform the
job.
3. The night
supervisor did
not know about

30. the job and thus
did not alert the
forklift drivers to
potential closed
aisles. Lack of
communication
between
supervisors
seems common.
4. The forklift
driver did not
realize that the
row was closed.
-------------C-ontinued on nexr page
89
90
;:. rrn<£o
Pa,t 171 · . A11ajytica/ Tech . 111q11es
CHANG E ANALYSIS OF
ACCIDENT EXAMPLE SC
SEQUENCE COMPARISON
5. No cones were
placed in the
aisles.
6· The forklift
driver could

31. ~ot clearly see
in front of the
forklift.
? . The forklift
driver was
driving faster
than the posted
speed.
8. The supervisor
was new to the
job.
SEQUENCE
5. Cones are
placed before
the barricades
to_alert forklift
drivers that
aisles are closed.
6. Forklift drivers
are able to
clearly see in
front of the
forklift.
7. Forklift drivers
do not exceed
posted speed.
8- Supervisors are
experienced.

32. DIFFERENCE
6. The forklift was
~verloaded and
it was difficult
for the driver to
see.
7· The forklift was
going too fast.
8- The supervisor
was inexper-
ienced.
ANALYSIS
S. ~e forklift
dnver Wasu
to seein Sed
pla~ed ~~:es
:amtenance
partment
when aisles
were closed.
6. The forklift-
driver was Jn
a hurry and
overloaded the
forklift.
7· The forklift
driver was
rushing to get

33. through the
shift.
8. The supervisor
was new to
supervision and
was used to
getting things
done instead of
using the proper
procedure.
Chapter 8: Cha11ge A11alysis
summary
,,,rysis is, simple technique for analyzing differences between
the
(l,Jl1l' ,cident sequence and the events 10 an accident-free
comparison
tfllSJJl~a . · . Changes are usually important factors 10 an
accident sequence.
~ence. . . . · ,,
01
,,
0
, change anal)~" companng the acodent sequence to a co
mparable
;~dent-fr« sequence is valuable in finding abstract causes o f
accidents.
lnfo!111'cion discovered during change analysis will help

34. prevent accidents
"" ,ecurring-(Please see the Appendix for a sample Change
Analysis form.)
REVIEW QUESTIONS
1.fof what types of accidents is change analysis most useful?
2. '1cltare the three types of accident-free situat io ns t hat ma
b
1oanaccident situation? Y e compared
c ange analysis?
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a_::th'.:o:r~ou~g~h~~
9 1
1
Course Learning Outcomes for Unit
Upon completion of this unit, students should be able to:
3. Apply accident investigation techniques to realistic case
study scenarios.
3.1 Develop a barrier analysis chart and worksheet for an
accident investigation.
4. Evaluate analytical processes commonly used in accident
investigations.
Reading Assignment

35. Chapter 8:
Change Analysis
Chapter 9:
Barrier Analysis
In order to access the resources below, you must first log into
the myWaldorf Student Portal and access the
Business Continuity & Disaster Recovery Reference Center
database within the Waldorf Online Library.
Kongsvik, T., Haavik, T., & Gjøsund, G. (2014). Participatory
safety barrier analysis: A case from the offshore
maritime industry. Journal Of Risk Research, 17(2), 161-175.
Pranger, J. (2009). Selection of incident investigation methods.
Loss Prevention Bulletin, 2009(209), 1-12.
Unit Lesson
In the previous unit, we learned that documenting the sequence
of events that led up to an accident is critical
to the accident investigation process. When conditions
surrounding each event are added to the timeline,
potential causal factors begin to emerge. However, an events
and causal factors chart by itself may not be
enough to identify all causal factors. It is a best practice to use
more than one analysis technique during an
accident investigation. Every technique has some limitations,
and using multiple techniques will improve the
reliability of the investigation conclusions (Oakley, 2012).
In this unit, we examine two analytical techniques: change
analysis and barrier analysis. Both are simple to
use, and both can provide significant insight into answering the

36. question of why an accident happened.
Change analysis is used to determine if there was a change in
procedures or conditions that led to an
accident. This is done by comparing the accident sequence
(which we have already determined using an
events and causal factors chart) to a sequence for the task where
an accident did not occur, to a set of
procedures that say how the task should be performed, or to an
imagined “ideal” sequence (Oakley, 2012).
Routine and repetitive tasks are good candidates for this
analytical technique. Change analysis is useful as
long as there is an accident-free situation that can be used for
comparison.
The changes between an accident sequence and an accident-free
sequence can be subtle and easily
overlooked. One of the potential weaknesses of change analysis
is that it might lead some investigators to
place blame for changes on the workers. Not all “changes” are
caused by the workers. For example, the
temperature may have been warmer in the accident sequence
than in the accident-free sequence, or perhaps
a new, unfamiliar product was being handled. It is best to use
change analysis in concert with one or more
additional analysis techniques.
UNIT STUDY GUIDE
Analytical Techniques I
2
UNIT x STUDY GUIDE

37. Title
Barrier analysis looks at the barriers that should have, or could
have, allowed the hazard to reach the target
(Oakley, 2012). Barriers are control functions that are designed
to stop the accident sequence at one or more
points. Note once again the importance of documenting the
event sequence when conducting accident
analysis. Barriers can be “hard,” like a machine guard or
personal protective equipment, which will prevent
physical contact with the hazard; however, barriers can also be
“soft,” like training and written procedures,
which, if followed, will prevent contact with the hazard.
Barriers can be categorized into three main types, which are as
follows (Oakley, 2012):
These categories will be helpful when we begin to identify
corrective actions. Barriers that fail often
correspond to engineering failures. Barriers not used may be the
result of poor decision making or inadequate
training. Barriers that did not exist often reveal flaws in the
hazard identification and control process.
Now, we need to return to the accident sequence presented in
Unit IV, and we will use it for a brief
demonstration of how change analysis and barrier analysis can
be applied.

38. On January 2, 2016, at 5:34 a.m., Sam, the night maintenance
technician, noticed a leak in the water pipe in
the valve department. The valve had been leaking for four
months, but because a maintenance request had
not been submitted, the problem was not fixed. Sam was about
to clock out at 5:40 a.m. and decided to leave
a note for Mary, the first shift technician, to mop up the area.
At 5:53 a.m., an air horn was sounded for
everyone to respond to an area. As workers arrived, they noted
that Bob (another employee) was lying in a
pool of water. It was very obvious to everyone that Bob’s leg
was broken. An ambulance was called, and, at
6:00 a.m., Bob was transported to the hospital. During the
investigation, it was learned that Sam had noted
the water but decided not to clean the area immediately. Sam
left a note at the desk at 5:41 a.m. and
departed the area. Mary was supposed to clock in at 5:40 a.m.,
but she called her supervisor, Tom, at 5:33
a.m.; she was unable to talk to him, so she left a message that
she would be arriving at 6:00 a.m. since she
was running late. Tom, the supervisor, also called at 5:33 a.m.,
and he left a message for Mary, saying that
he was running 15 minutes late. Mary, who arrived at 5:53 a.m.,
heard the alert horns and responded to the
accident.
To see the events and causal factors chart for this accident,
click here.
Change Analysis
For demonstration purposes, we will use an ideal situation as
our comparison accident sequence. We see
that if there was no water on the floor, Bob would not have
slipped and fallen. Of course, we need to look a bit

39. further into the event sequence that resulted with the water on
the floor. In an ideal situation, the leak would
have been fixed when it was first discovered. In an ideal
situation, Sam would have cleaned up the water
when he noticed it. Finally, in our ideal situation, the
communication between Tom and Mary could have been
more effective.
To see the change analysis chart for the accident, click here.
We did not identify anything different than what we had
included in the earlier events and causal factors chart,
but the change analysis format provides a better opportunity to
lead us to possible corrective actions. The
analysis clearly shows responsibility at the worker, supervisor,
and management levels.
Barrier Analysis
The hazard in our accident scenario is the water on the floor.
The target is Bob, the injured worker. Our
analysis needs to identify barriers that could have prevented
Bob from coming in contact with the water.
Brainstorming barriers might result in a list, such as follows:
–
not used or does not exist);
barrier – not used or does not exist);
https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZUL
U/EmergencyServices/OSH/OSH4601/W15Jc/UnitIV_ECF_Even
ts_and_Conditions.docx
https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZUL
U/EmergencyServices/OSH/OSH4601/W15Jc/UnitV_Change_A

40. nalysis.docx
3
UNIT x STUDY GUIDE
Title
– not used or does
not exist); and
res (administrative barrier – not used or
does not exist).
There are many ways to look at barriers. If we knew that a
procedure requiring a “wet floor” sign did exist,
then we could say it was an engineered barrier that was not
used. An analysis is likely to change as more
information is revealed. Root causes are discovered only after
extensive investigative work.
To see the barrier analysis chart for the accident, click here.
The barrier analysis chart accomplishes the following: contains
additional information discovered after the
initial brainstorming of possible barriers, leads us directly to
causal factors, and starts us on the path to
possible corrective actions. Note that it also provides a bit more
depth on causal factors than provided by the
change analysis.
Change analysis and barrier analysis are easy to use and, when
used together, complement each other well.
In the next unit, we will examine more techniques that can be
used.

41. Reference
Oakley, J. S. (2012). Accident investigation techniques: Basic
theories, analytical methods, and applications
(2nd ed.). Des Plaines, IL: American Society of Safety
Engineers.
Suggested Reading
To learn more about conducting accident investigations, take a
few minutes to read the report below. It
explores some major methods of accident investigation that are
being used, and it discusses the application
of these methods.
Sklet, S. (2002). Methods for accident investigation. Retrieved
from
http://frigg.ivt.ntnu.no/ross/reports/accident.pdf
This handbook, created by the U.S. Department of Energy,
provides a sequential process for conducting
accident investigations. The document assists in determining
how and why an accident happened, and the
document touches on how to develop conclusions to prevent the
accident from happening again.
U.S. Department of Energy. (2012). Accident and operational
safety analysis: Volume I: Accident analysis
techniques. Retrieved from
http://energy.gov/sites/prod/files/2013/09/f2/DOE-HDBK-1208-
2012_VOL1_update_1.pdf
https://online.waldorf.edu/CSU_Content/Waldorf_Content/ZUL
U/EmergencyServices/OSH/OSH4601/W15Jc/UnitV_Barrier_An
alysis.docx

42. Events and Conditions
No direct communication to anyone prior to leaving
No one to act on messages
Clean up of floor not done immediately
No “wet floor” signs placed
Leak not repaired for four months
1/2/16 – 5:33 am Mary leaves message for Tom
(supervisor)
1/2/16 - 5:53am Bob found lying in pool of water
1/2/16 – 5:53 am Air horn sounds
1/2/16 – 5:34 am Sam notices leak and wet floor in valve
dept.
1/2/16 – 5:41 am Sam leaves note for Mary to mop
up wet floor
1/2/16 5:41 am
Sam goes home
1/2/16 – 5:33 am Tom leaves message for Mary
Emergency response was good

43. 1/2/16 – 6:00 am Ambulance transports Bob to hospital
Key:
Condition
Event
Accident
Change Analysis
ACCIDENT SEQUENCE
COMPARISON SEQUENCE
DIFFERENCE
ANALYSIS
1. Sam did not clean up the water.
Sam cleans up the water.
No water on the floor.
No clear requirement for immediate cleanup of spills.
2. Maintenance request to repair valve was not submitted.
Maintenance request submitted as soon as leak is discovered.
No potential for water on the floor.
Valve department supervisor did not submit valve repair
request.
3. Mary and Tom both called to say they would be late to work.
Neither one saw the other’s message; no one saw Sam’s note; no
one cleaned up the spill.
Messages from Mary and Tom are passed to another manager,

44. who takes action. Sam’s message is seen, and spill is cleaned
up.
Increased chance that spill is discovered and cleaned up before
someone slips and falls.
No one on the morning shift was aware of the spill due to poor
communication.
Unit Assignment
Barrier Analysis Worksheet Project
Read the U.S. Chemical Safety Board investigation report of the
2007 propane explosion at the Little General Store in Ghent,
WV.
NOTE: This is the same investigation report used to create the
events and causal factors (ECF) chart in Unit IV. Complete the
assignment as detailed below.
Part I: From the information in the report, create a three-column
barrier analysis worksheet. Use the sample form on page 173 of
the course textbook as a template, and follow the instructions
below:
1. In the first column, list the barriers. Group the barriers by
category (failed, not used, did not exist).
2. In the second column, describe the intended function of each
barrier.
3. In the third column, evaluate the performance of the barrier.
Part II: On a separate page, discuss the potential causal factors
that are revealed in the analysis. Are there additional causal
factors that were not identified in the ECF chart you created in
the Unit IV assignment? This part of the assignment should be a
minimum of one page in length.
Upload Parts I and II as a single document. For Part II of the
assignment, you should use academic sources to support your
thoughts. Any outside sources used, including the sources
mentioned in the assignment, must be cited using APA format
and must be included on a references page.

45. Barrier Analysis
BARRIER
PURPOSE OF BARRIER
PERFORMANCE OF BARRIER
1. Maintenance procedures
Ensure maintenance requests are submitted and acted on in a
timely fashion.
This barrier failed since the valve department supervisor was
not trained in maintenance request responsibilities.
2. Job Procedures - Housekeeping
Establish expected levels of safety for all tasks.
This barrier failed because the worker failed to follow the
procedures for cleanup of spills.
3. Barricade
Warn other workers of a hazardous situation.
This barrier did not exist – there are no written procedures
requiring the use of “wet floor” signs.
4. Communication
Ensure emergency information is shared and acted on.
This barrier did not exist – there are no established procedures
for relaying emergency information.
Unit Quiz
QUESTION 1
Which of the following statements is TRUE?
Change analysis can only be used proactively.
Change analysis should not be used to evaluate processes.

46. Change analysis can be used reactively.
Change analysis should not be combined with other techniques.
QUESTION 2
Which of the following questions is NOT typically asked about
each event when conducting a change analysis?
1.
What happened?
Why did it happen?
When did it happen?
Where did it happen?
QUESTION 3
Which type of barrier analysis works best for accident
investigations?
1.
Energy trace and barrier analysis (ETBA)
Barrier and control analysis (BCA)

47. Job safety analysis
Hazard-barrier-target (HBT) analysis
QUESTION 4
What are the two products of barrier analysis?
1.
Hazards and targets
Targets and barriers
Chart and analysis worksheet
Worksheet and report
QUESTION 5
Which of the following statements is FALSE?
1.
Change analysis must be structured.
Change analysis should not be detailed.
Change analysis should include management systems events.
Change analysis should include every event that changed.

48. Board Question
Using an injury scenario at work or at home that happened to
you or someone you know, discuss some hard and soft barriers
that, if in place, might have prevented the incident.