• REACH’s influence in establishing de
facto limits (derived no-effect levels,
or DNELs)
• a lack of understanding of the differ-
ence between acceptable risk and a
true threshold of toxic risk
Although these challenges are sub-
stantial, the speakers and audience
agreed that countries motivated by the
common goal of protecting human health
can set up a process for sharing scientific
information, develop exposure limits, and
align on the documentation for those
limits. Leadership of this collaborative ef-
fort would reside with a neutral third
party, preferably an international body.
The group also suggested that volun-
teerism, the hallmark of OEL-setting thus
far, could not carry the process forward.
And finally, funding must be made avail-
able to support this effort for the global
community. Presentations are posted at
www.ioha.net/internationaloelssues.html.
Another approach is to take advantage of the cross-sensitivity of the CO
working electrode in an unfiltered carbon monoxide sensor. Substance-spe-cific CO sensors normally include a
robust internal filter designed to remove H2S and other contaminants before they reach the sensing electrode.
When the filter is left out of the design,
H2S readily diffuses into the sensor and
is detected by the CO electrode. The
signal output of this type of sensor is
generally much stronger for H2S than
for CO. Some manufacturers use the
single signal to calculate two readings.
Each reading assumes that the entire
signal is due to the presence of one or
the other gas. Some manufacturers use
the ratiometric difference between the
signal strength for the two gases and
simply set the CO sensor alarm at a
concentration equivalent to the desired
“take action” concentration limit for
H2S. The obvious drawback with this
approach is that the user will not know
which gas is present, or the relative
concentrations of each. Manufacturers
do not usually require calibration of
this type of sensor using both gases,
but calibration is usually with CO only,
which is generally much less expensive
and stable for a much longer period
than calibration gas that includes H2S.
Future Collaboration
The October 2010 Professional Conference on Industrial Hygiene in Ft. Worth,
Texas, continued the dialogue with a
half-day session on OELs that included
presentations on ACGIH’s processes for
setting TLVs, OSHA’s preliminary deliberations on updating PELs, DNELs as de
facto OELs, and the pharmaceutical industry’s reliance on control banding and
its use of risk modeling when data are
limited. These presentations are accessible at www.pcih2011.org.
Efforts to define an “acceptable exposure level” continue at the national and
international levels. Although approaches
to this task vary, the discussions at IOHA
and PCIH revealed that we have a better
understanding of the challenges. While
no unitary solution is expected immediately, the conversation on OELs enables
a more robust future collaboration.
Conclusion
Electrochemical H2S sensors based on
oxidation of the target analyte at a
working electrode are among the most
dependable, stable, and reliable type of
gas-detecting sensors available. However, no sensor can detect gas unless it
is used. The only way of being sure that
toxic contaminants are not present in
dangerous concentrations is to look for
them with an atmospheric monitor designed for their detection. To protect life
and health, it is important for industrial
hygienists to understand their detection
instrument. Using the instrument when
needed to detect a dangerous airborne
contaminant such as H2S is critical.
PhilSmith,PhD,CIH,isanindustrialhygienistwith
theUSDOL-OSHAHealthResponseTeam,in
Sandy,Utah,andisthecurrentchairoftheAIHA
Real-TimeDetectionSystemsCommittee.Hecan
bereachedatSmith.Philip.A@dol.gov.
BobHenderson,MBA,ispresidentofGfGInstru-mentation,Inc.,pastchairoftheAIHAReal-Time
DetectionSystemsCommittee,pastchairofthe
AIHA Confined Spaces Committee, and past chair
oftheInternationalSafetyEquipmentAssocia-tion’sInstrumentsProductGroup.Hecanbe
reachedatbhenderson@gfg-inc.com.
CONNECT for CREDIT
www.aiha.org/syntestseries
ChrisLaszcz-Davis,MS,CIH,REA,isprincipal,The
Environmental Quality Organization, LLC, in
Lafayette,Calif.,presidentoftheCaliforniaIndustrial
Hygiene Council (CIHC) and former V.P., EH&S,
KaiserAluminum&ChemicalCorporation.Shecan
bereachedatChrisLD@EQ-Organization.comor
(925) 330-1774.
SusanD.Ripple,MS,CIH,istheNorthAmericaIn-dustrial Hygiene Expertise Center resource leader
andprincipalcoordinatorforoccupationalexposure
limits at The Dow Chemical Company in Midland,
Mich.Shecanbereachedatsdripple@dow.comor
(989) 636-5572.
LucHamelin,ROH,CIH,CSP,CRSP,isassistantdi-rectorforthePrevention&SafetyDepartmentat
UniversitéduQuébecàMontréal(UQAM)inMon-
treal,Quebec.Hecanbereachedat(514)987-3000
ext.0872orhamelin.luc@uqam.ca.
JimmyL.Perkins,PhD,CIH,isaprofessorinthe
UniversityofTexasSchoolofPublicHealthSanAn-tonio. He can be reached at (210) 562-5502 or
perkinsjl@uthscsa.edu.
CONNECT for CREDIT
www.aiha.org/syntestseries
References
