Why Bump Testing Saves Lives
New data reveals the correlation between
bump test intervals and gas detector failures
By: Dave Wagner, Director of Product Knowledge, Industrial Scientific Corporation
Why do I have to bump test my gas detectors?
This is a common response that many manufacturers and
industry associations hear when they recommend “bump”
testing gas detectors prior to each day’s use.
In the past, the reasons for this may
have been hard to understand. Without
quantifiable evidence, the importance
of bump testing was often lost in a
deluge of other safety best practices and
recommendations. A few years ago,
misleading information about so-called
“maintenance-free” gas detectors only added
to the confusion.
Analysis powered by data from:
• 1 billion+ datalogged readings
• 4.7 million+ bump test records
• 2.5 million+ alarm events
• 1.1 million+ calibration records
• 27,000+ gas detectors
• 1,100+ customer sites
Over the past seven years, we have collected and
monitored data from tens of thousands of gas
detectors. A recent analysis of this data has
produced some surprising results. Now, we
have hard evidence that supports the
need for routine bump testing.
In this paper, we will explore these findings
and demonstrate the life-saving importance
of bump testing prior to each day’s use.
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Why Bump Testing Saves Lives
Bump Test Defined
A “bump” test of a portable gas detector
is performed in order to verify the
functionality of sensor(s) and alarms. The
test is performed by briefly exposing the
instrument to a known concentration(s)
of the target gas(es) and verifying that the
instrument responds accordingly.
Bump tests verify
the gas detector’s
alarm functions by
simulating alarm
conditions for each
sensor.
The bump test is only a verification
of functionality. It is not designed
nor intended to measure a gas
detector’s accuracy. Therefore, the
concentration of gas used in the
exposure is not critical; but it should
be higher than the alarm settings for
each sensor.
Simply stated, bump tests verify the gas
detector’s alarm functions by simulating
alarm conditions for each sensor.
This is necessary considering that the output
of a typical gas sensor in clean air is zero.
That’s the same as the output of a nonfunctional or dead sensor. So exposing the
instrument and sensors to gas is the only
way to know that the sensor will respond to
dangerous gas in the atmosphere.
... 3 gas detectors
out of every 1,000
will fail to respond
properly to gas
during a bump test
on any given day.
Bump Test History
In the pre-confined-space era of gas
detection, portable gas detectors
were characterized by analog meter
movements, LED indicators, and in
some cases, crude digital displays
tied to analog electronic systems.
Instruments were used primarily for
declassifying areas in hot work operations;
or for detecting dangerous levels of methane
or oxygen depletion in mining applications.
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These instruments were considered to be
more analytical in nature and more precise
than their technology permitted. Therefore,
many manufacturers recommended
calibration prior to each day’s use to ensure
functionality and accuracy.
Then confined space legislation went into
effect in the United States in 1993 and
later in the UK in 1997. As a result, the
use of portable gas detection instruments
proliferated worldwide. With widespread
use in virtually every industrial environment,
performing calibration prior to use on large
fleets of gas detectors became onerous and
economically burdensome.
The legislation required instruments to
be calibrated according to manufacturer’s
recommendations. This led to end user
requests for manufacturers to reduce these
requirements and ease their customers’ pain.
This gave birth to the bump test as a way
to ensure that instruments were tested prior
to use while reducing the recommendations
for calibration; saving customers time and
money.
Today, the term “bump test” is part of the
regular vocabulary of every manufacturer
and end user of portable gas detectors.
Analysis of Bump Test Failure Data
Industrial Scientific Corporation collects
data from portable gas detectors used
in the field through iNet, a premier fleet
monitoring service. Collected data includes
calibration and bump test records, diagnostic
test information, gas readings and alarm
events uploaded from the datalogging
memory of each gas detector.
In all, the iNet database holds more than 1
billion datalogged gas readings, 4.7 million
bump test records, 1.1 million calibration
records and 2.5 million gas alarm events.
This data has been uploaded from more than
27,000 gas detectors used in over 1,100 enduser locations.
Analyzing this data has revealed that the
incidence of bump test failure in instruments
tested on a daily basis is approximately
0.3%. That failure rate appears to be trivial.
But in practical terms, it means that 3 gas
detectors out of every 1,000 will fail to
respond properly to gas during a bump test
on any given day. The plot below shows
that increasing the bump test interval to 20
days doubles the expected failure rate.
A further study combined this test data
with an analysis of how frequently gas
detectors are exposed to hazardous, alarming
conditions. The study found that, on
average, one out of every 100 gas detectors
not bump tested before use will fail to
respond and alarm properly to an actual gas
alarm event every 25 days.
Why Bump Test Failures Occur
Why do bump test and instrument
failures occur? Does the frequency of
failure reflect poorly on the quality
and reliability of the product? Most
often, failure is not attributed to the gas
detector or the gas sensors themselves.
Failure is created in the environments
that the instruments are used in and the
manner in which they are used.
Failure is created in
the environments
that the instruments
are used in and the
manner in which
they are used.
Portable gas detectors are used in harsh
applications. They are dropped from high
places and subjected to extreme shock.
They are exposed to extreme temperatures
and humidity, and to dust, water and mud.
Delicate sensors and electronics can be
damaged by shock. Sensor membranes
and openings can also be blocked by debris
preventing gas in the atmosphere from
reaching the sensors.
The damage to the instrument in these
cases is not always visible and may only be
apparent when a bump test failure occurs.
(Continued)
Probability of Bump Test Failure
Test Failures (%)
0.014
0.012
0.01
0.008
Probability of Failure
0.006
0.004
0.002
0
0
10
20
30
40
Bump Test Interval (Days)
New data supports manufacturers’ recommendations for a daily bump test. This graph shows
that the bump test failure rate in instruments tested on a daily basis is approximately 0.3%.
Increasing the bump test interval to 20 days doubles the expected rate of failure.
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Why Bump Testing Saves Lives
Why Bump Tests are Important
On any given day,
1 in every 2,500
untested instruments
will fail to respond
to a dangerous
concentration of
gas.
Failure can also be attributed
to improper maintenance as
demonstrated in the following
documented incident: Workers in
a refinery control room noticed the
smell of gas during a routine shift.
They contacted their plant safety
department, which sent a portable
gas detector to test the atmosphere.
After several minutes, the instrument
showed that no gas was present.
With the odor from the gas strengthening,
the workers decided to evacuate the control
room. As they left the area, one of the
workers ignited a blast that catastrophically
damaged the control center. Luckily,
there were no fatal injuries.
The daily bump test
is the only way to
detect these failures
before they occur.
An investigation revealed why the
gas detector failed to see the gas. An
improper calibration prevented the
gas detector from responding to the
hazard and producing an alarm.
If a simple bump test had been performed
before the gas detector was used, the
incident would have been avoided.
Bump Test Gas Detectors Daily
Portable gas detectors are precise electronic
devices that play a critical role in protecting
workers. Their ability to do their job
properly is not always visually apparent.
On any given day 1 in every 2,500 untested
instruments will fail to respond to a
dangerous concentration of gas. The daily
bump test is the only way to detect these
failures before they occur. Don’t take your
gas detector to the job and rely on it to save
your life without testing it first.
Tools to Automate Bump Tests
Many organizations find it difficult to bump
test gas detectors this frequently. They may
also want these tests performed consistently
and without operator error.
Calibration stations and docking systems
have made these challenges easy to
overcome. They also save the time that it
would take for an operator to perform the
same function manually.
Another option that has gained momentum
in recent years provides Gas Detection as a
Service. Industrial Scientific’s iNet is the
only choice that combines these automated
functions with automatic equipment
replacements. Plus, subscribers have full
visibility into their gas detection program.
Hosted software shows trends and data
related to their gas detector alarms, exposure
and usage. That way, safety managers have
the tools they need to address problems
before they happen.
Find out which solution is the best fit for
you. Contact Industrial Scientific for a free
evaluation of your gas detection program.
© 2009 Industrial Scientific Corporation
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