TWA for H2S Exposure ???
Ken Navarre
An office worker at a publicly owned sewage treatment facility has
measurable levels in her office building and is seeking the permissible
exposure over an 8 hr day.
An MSDS would be helpful...
Thanks in advance.
--
Ken Navarre
k...@netcom.com
John Douglas Porter
According to:
"TLVs (registered trade mark) Threshold Limit Values and Biological
Exposure Indices for 1986-1987", American Conference of Governmental
Industrial Hygenists, Second Printing, 1986, p.21. ISBN 0-936712-69-4
Hydrogen sulfide [CAS 7783-06-4] TWA = 10 ppm, 14 mg/m^3
STEL = 15 ppm, 21 mg/m^3
From p.3:
"The Threshold Limit Value-Time Weighted Average (TLV-TWA) -- the
time-weighted average concentration for a normal 8-hour workday and a
40-hour workweek, to which nearly all workers may be repeatedly exposed,
day after day, without adverse effect."
"Threshold Limit Value-Short Term Exposure Limit (TLV-STEL) -- the
concentration to which workers can be exposed continuously for a short
period of time without suffering from 1) irritation, 2) chronic or
irreversible tissue damage, or 3) narcosis of sufficient degree to
increase the likelihood of accidental injury, impair self-rescue or
materially reduce work efficiency, and provided that the daily TLV-TWA is
not exceeded. It is not a separate independent exposure limit, rather it
supplements the time-weighted average (TWA) limit where there are
recognized acute effects from a substance whose toxic effects are
primarily of a chronic nature. STELs are recommended only where toxic
effects have been reported from high short-term exposures in either humans
or animals.
A STEL is defined as a 15-minute time-weighted average exposure which
should not be exceeded at any time during a work day even if the
eight-hour time-weighted average is within the TLV. Exposures at the
STEL should not be longer than 15 minutes and should not be repeated more
than four times per day. There should be at least 60 minutes between
successive exposuresat the STEL. An average period other than 15 minutes
may be recommended when this is warranted by observed biological effects."
The publication emphasizes that interpretation of TLVs should be left to
qualified professionals trained in industrial hygene. Requests for
interpretation of TLVs "must be in writing, in care of the Executive
Secretary ACGIH". The Annals of ACGIH publishes the written
interpretations. You should check there to see if hydrogen sulfide has
been covered.
The address of ACGIH is:
ACGIH, 6500 Glenway Ave., Bldg. D-7, Cincinnati, OH 45211-4438
(513) 661-7881.
There is also a companion volume which gives scientific information and
references to works consulted in preparing the TLVs.
You could also consult the Merck Index.
J.P.
gro...@esvx12.es.dupont.com
An ALDRICH MSDS sheet lists under Section 15. Regulatory Info:
ACGIH TLV-TWA 10 ppm; STEL 15 ppm
I would suggest that you call SIGMA-ALDRICH Corp.at 1-800-231-8327
for Technical Service or FAX them at 1-800-962-9591 and they may send you
an MSDS hard copy.
hamil...@kosmos.wcc.govt.nz
The 1990-91 ACGIH "Guide to Occupational Exposure Values" lists
TWA STEL/CEIL (C)
ppm mg/m3 ppm mg/m3
ACGIH TLV 10 14 15 21
OSHA PEL 10 14 15 21
NIOSH REL C10 C15 (10 min)
DFG MAK 10 15
>An office worker at a publicly owned sewage treatment facility has
>measurable levels in her office building and is seeking the permissible
>exposure over an 8 hr day.
Anyone who has visited Rotorua in NZ will know how your sense of
smell is soon overwhelmed by H2S. As another poster has pointed out,
if there are detectable significant levels in the office, then the
source is likely to be much higher, and should be identified and
corrective action taken. ( extraction/ventilation/relocation/etc )
Bruce Hamilton