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Developing a Voluntary Safety Standard for Step Stools

Authors:
  • Loring Human Factors, LLC

Abstract

American Institutes for Research (AIR) assisted the Consumer Product Safety Commission (CPSC) to identify the human factors issues that should be addressed in a forthcoming voluntary safety standard for step stools. According to CPSC data, older people, children, and women of all ages are over-represented in step stool accidents. We studied the accident scenarios, recommended requirements for step stools, and evaluated the completeness of a draft of the standard with respect to user interaction.
PROCEEDINGS
of
the
HUMAN FACTORS
SOCIEn'
33rd
ANNUAL MEETING-I989
DEVELOPING A VOLUNTARY
SAFETY STANDARD FOR STEP STOOLS
Beth
A.
Loring
American Institutes for Research
Bedford.
MA
ABSTRACT
American Institutes for Research (AIR) assisted the Consumer Product
Safety Commission (CPSC) to identify the human factors issues that
should be addressed in
a
forthcoming voluntary safety standard for step
stools. According to CPSC data, older people. children. and women of
all
ages
are
over-represented in step stool accidents.
We
studied the
accident scenarios. recommended requirements for step stools. and
evaluated the completeness of
a
draft of the standard with respect to
user
interaction,
THE
NEED FOR
A
STEP
STOOL
STANDARD
According to the U.S. Consumer
Product Safety Commission (CPSC).
step stool injuries result in about
three
times
as
many hospitalizations
(12%)
as
the average of
all
National
Electronic Injury Surveillance System
(NE1SS)-reported injuries (Present.
1983). In September 1985, the CPSC
and the American So,ciety for Testing
and
Materials
(ASTM) held
a
joint
conference on Safety for Older
--_--
Consumers, and determined that
a
voluntary safety standard for step
stools
was
needed. While
ASTM
was
well-prepared to develop strength and
construction requirements, the CPSC
recognized the need to evaluate the
completeness of the standard with
respect to user interaction.
We
at
American Institutes for Research
assisted the CPSC in determining the
human factors issues to be addressed
in the standard.
WHO
IS
INJURED
MOST OFTEN
AND
HOW?
With CPSC's direction. this two-
year study
was
limited to three types
of step stools:
(1)
chair stools.
which have steps and
a
seat.
(2)
folding stools. which may look like
miniature step ladders or have an
llX1l
or frame construction, and
(3)
utility stools. which have
a
single
platform about ten inches off the
floor. Spring-loaded. library type
stools also fall into the third
category.
We
performed background
studies to define the scope and
nature of human factors requirements.
We
developed our recommendations
independently from the committee
writing the standard in order to
provide
a
viewpoint emphasizing human
factors objectives.
Problem Assessment
--------------
We
first
analyzed in-depth and
summary accident data from the NEISS.
The accident data included
information about the age,
sex
and
health of the victims,
as
well
as
information about the products
involved and how the accidents
occurred. From this data and
previous studies performed by the
CPSC on step stool safety (eg.
Present. 1983).
we
found trends in
the demographics of step stool
accident victims and created
a
list
of the most common accident
scenarios. Older consumers (people
over 55) and children under
five
are
the high risk groups. Women make up
the majority of
victims
by
almost two
to one (see Figure
1).
Seventy-five
percent of the victims in one ten-
year study
were
over
65
years of age
(Present. 1983). The most common
scenario involved people losing their
balance while standing or kneeling
on
the stool. Other common scenarios
were:
the stool folded and col-
lapsed; the stool broke and
collapsed; the person fell while
descending; and the person
fell
from
a
seated position.
We
also learned
that:
a
the majority of the step stools
were
metal
most step stools
were
used
indoors
the products ranged in age from
5
to 25 years
479
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ANNUAL MEETING-I989
non-skid step surfaces
were
absent in wood models. but
included in
metal
step stools
the victims usually had something
in their hands
the victims were usually standing
and reaching while on the stool
This information and data gathered
through morphological charting of
step stools on the market uncovered
the most critical areas of needed
safety improvements.
Next,
we
observed and videotaped
people performing structured tasks
with each of seven sample step
stools. The tasks
were
representa-
tive of common step stool usage.
Through task analysis
we
identified
(a) body positions during opening,
carrying, positioning, ascending,
standing. reaching. sitting.
descending. and closing, (b) varia-
tions in interaction from one person
to another and among various types of
stools. and (c) errors users made and
problems they encountered. We
surveyed the subjects to provide in-
sight into their preferences and
attitudes toward step stools.
Without this information,
we
could
have overlooked safety requirements
that
were
not identified in the
CPSC
statistics.
RECOMMENDED
HUMAN
FACTORS
REQUIREMENTS
Using the most common accident
scenarios.
we
created fault
trees
to
aid in-developing recommended human
factors requirwents for the
standard. The fault
tree
analysis
uncovered the primary factors con-
tributing to the accidents in each
scenario. From this.
we
developed
a
list
of the issues contributing to
step stool safety:
sturdiness
stability
slip resistance
ease and safety of use
discouraging unsafe behavior by
the user
We
identified the functional charac-
teristics influencing these five
issues. and defined the unsafe
behaviors that should be discouraged.
We
were
then able to define the scope
of the requirements. The requirements
were
performance-based rather than
prescriptive in that they were not
intended to restrict design freedom.
For
example, one of our requirements
stated "The spreading mechanism (for
folding stools) shall provide
a
positive lock to prevent inadvertent
closing."
We
did not specify the type
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of locking mechanism. since many
designs would be effective.
We
did
not address issues relating to the
physical strength of the
materials
used unless they directly affect the
human factors
of
the step stool.
EVALUATION
OF
THE
DRAFT STANDARD
When
a
draft of the standard
became available (ASTM. 19881,
we
created
a
cross-reference
matrix
to
show where the standard addressed
human factors issues and
areas
where
it
did not. For example. the
standard requires
at
least
one and
one-half threads of each bolt to be
exposed beyond the nut. but does not
define
a
maximum number of threads
that can be exposed. Such
a
require-
ment
is
necessary, since the
CPSC
has
received complaints about step stools
having bolts that protrude danger-
ously. These bolts have caused users
to injure themselves (NEISS, 1987).
We
also critiqued the organization of
the standard and
its
readability and
usability. based on past experience
in document design (Felker
et
al.,
1988).
In general. the draft ASTM
standard
is
well
prepared, and an
important step forward. However,
there
are
areas
in which
it
does not
address human factors engineering
considerations. Specifically, the
following design considerations
should be considered
as
additions to
the standard:
the position of the stepping
surfaces with respect to the
footprint of the stool on the
floor, to reduce the chance that
the stool
will
tip when people
lean over
the proportion of stool height to
width. to eliminate
tall,
narrow
stools that tip easily from side
to side
the maximum weight of the step
stool.
so
that people with
limited strength, particularly
the elderly,
are
not injured
trying to lift the stool
the appearance
of
areas.
such
as
seats.
that
are
not meant to be
used
as
steps,
so
that they do
not have
a
step-like appearance
we
an indication of the orientation
of the
step
stool,
so
that people
do not step off on the wrong side
of the stool. expecting the steps
to be there
the need for
little
or no routine
maintenance. since people tend to
use step stools on the spur of
the moment and
it
is
unlikely
that they
will
consider
maintenance on
a
routine basis
the maximum inclination of the
steps, to reduce the chance of
people falling backward
(particularly when no handhold
is
provided),
or
falling during
descent because
a
step could not
be easily located
safe and easy operation of the
spreaders and hinges to eliminate
pinch points and the need for
excessive force
the addition of locking
mechanisms on the hinges, to
prevent inadvertent collapse,
particularly to protect the hands
of children
the minimum force required to
operate spring-loaded
casters,
so
that
a
small
weight
is
sufficient
to cause them to compress.
allowing the
rim
of the stool to
form
a
seal with the floor
the
ease
of understanding the
instructions for assembly, use,
and maintenance
the design. height. and diameter
of hand holds. which should be
considered
as
safety features and
would particularly help the
elderly
In the last phase of the project.
tested
a
sample of seven step
stools using the procedures described
in the draft standard and reported
areas
where the procedures
were
successful and
areas
where they could
be improved.
We
evaluated the tech-
nical accuracy and appropriateness of
the proposed values (e.g.. "the step
stool shall not slip more than
1/4
inch when the force
is
applied") by
comparing the
values
with (a) perfor-
mance standards for step ladders
(ANSI, 19821, (b) data in human
factors literature. (c) our previous
481
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research on the step stool problem,
and
(d)
our experience during
testing
.
In the process, we recorded the
performance of each individual step
stool. It was notable that six of
the seven step stools we tested did
not pass all of the tests, and conse-
quently would not be acceptable
according to the draft standard.
CONCLUSION
The draft standard is a step
toward improving the safety of this
common household product. However,
it could be improved by addressing
more than safety as related to the
quality of manufacturing and strength
of materials. It needs to address
the human interaction issues
necessary to ensure safe use. We
expect that the final standard will
incorporate test procedures that
evaluate the safety of interaction
between people and step stools.
REFERENCES
American National Standards
Institute. "American National
Standard for Ladders
-
Portable
-
Safety Requirements.11 ANSI A14.1.
A14.2, and A14.5, 1982.
American Society for Testing and
Materials. "Standard Consumer
Safety Performance Specification
for Step Stools (Fourth Draft)."
ASTM. August, 1988.
Felker, G. and others. Guidelines
for Document Designers,
Washington, D.C.: American
Institutes for Research, 1981.
National Electronic Injury
Surveillance System
(NEISS).
Statistics collected on step
stool-related accidents, 1987.
Present,
P.
"Step Stools." U.S
Consumer Product Safety
Commission, Sept 1983.
482
at HFES-Human Factors and Ergonomics Society on April 26, 2016pro.sagepub.comDownloaded from
ResearchGate has not been able to resolve any citations for this publication.
Standard Consumer Safety Performance Specification for Step Stools (Fourth Draft)
American Society for Testing and Materials. "Standard Consumer Safety Performance Specification for Step Stools (Fourth Draft)." ASTM. August, 1988.
American Institutes for Research, 1981. National Electronic Injury Surveillance System (NEISS) Statistics collected on step stool-related accidents
  • G Felker
  • Guidelines
  • For Document Designers
  • D C Washington
Felker, G. and others. Guidelines for Document Designers, Washington, D.C.: American Institutes for Research, 1981. National Electronic Injury Surveillance System (NEISS). Statistics collected on step stool-related accidents, 1987.
National Electronic Injury Surveillance System (NEISS)
  • G Felker
  • Others
Felker, G. and others. Guidelines for Document Designers, Washington, D.C.: American Institutes for Research, 1981. National Electronic Injury Surveillance System (NEISS). Statistics collected on step stool-related accidents, 1987. Present, P. "Step Stools." U.S Consumer Product Safety Commission, Sept 1983.