topic 3 occupational health standards · pdf file–4 hours @ 11 ppm, ... simplest form,...
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1
Topic 3
OCCUPATIONAL HEALTH
STANDARDS
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Threshold Limit Value (TLV)
Threshold limit values (TLVs)refer to airborne concentrations of substances and represent conditions under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects
Because of wide variation in individual susceptibility, however, a small percentage of workers may experience discomfort from some substances at concentrations at or below the TLV
A smaller percentage may be affected more seriously by aggravation of a pre-existing condition or by development of an occupational illness
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TLV (USA)
Published by ACGIH
Established in 1946 (updated annually)
Approximately 750 chemicals covered
Guidelines not law
Documentation of TLVs and BEIs
“Balancing of health considerations and cost to industry”–ACGIH 1948
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Examples of TLV
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5
Standards of Exposures (USECHH
2000)
"permissible exposure limit" means a ceiling limit or an eight-hour time-weighted average airborne concentration or the maximum exposure limit;
"ceiling limit" means the airborne concentration that should not be exceeded during any part of the working day;
"time-weighted average" in relation to airborne concentration, means an average airborne concentration over a specified period of time;
"maximum exposure limit" means a fifteen-minute time-weighted average airborne concentration which is three times (3x) the eight-hour time-weighted average airborne concentration of the chemicals specified in Schedule I; - same as STEL (ACGIH)
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6
Threshold Limit Value (ACGIH)
1. TLV-TWA Threshold Limit Value – Time Weighted Average (TLV-TWA): 8 Hour time weighted average
2. Time Weighted Average– Short Term Exposure Limit (TLV-STEL): TLV for short term exposure, Contaminant concentration averaged over a 15-minute period
3. Threshold Limit Value-Ceiling (TLV-C): maximum concentration that cannot be exceeded at any time / location at work. This is an instantaneous concentration; or concentration averaged over a 15 minute period if technology does not exist to measure instantaneous concentrations
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General Formula for TWA
n
i
i
n
i
ii
t
tc
TWA
1
1
ci is concentration during ith interval
ti is duration of the ith interval
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Evaluating Exposure to Volatile Toxicant
by Monitoring
Worker exposures using online continuous monitoring of
air concentrations of toxicants (C), the measured time–
weighted average concentration is,
8
wt
dttCTWA08 )(
8
1
TWA is time weighted average (concentration)
C(t) is concentration in ppm or mg/m3 of chemical in air
tw is the worker shift time in hours
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For workers exposed for more than 8
hour
Since the computation is normalized to 8
hours, if workers are exposed to TLV~TWA
level for 12 continuous hours, then
TWA=(8/12)(TWA8)
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8-hour Time Weighted Average
10
For a worker who works at various locations in
the plant, his/her exposure is measured using
intermittent samples at fixed points,
8
)(...)()(1 2
0 00 21
8
t t
n
t n
dttCdttCdttCTWA
82211
8nnctctct
TWA
...
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Example
PEL for the chemical involved is 12 ppm
Partial period samples
– 4 hours @ 11 ppm, 2 hours @ 14 ppm, 2 hours @ 20 ppm
TWA calculation
14ppmTWA
hr 2)2(4
m)(2hr)(20ppm)(2hr)(14ppm)(4hr)(11pp
TWA
Health risk? Risky…why?
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TLV for Mixture
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Evaluation of Exposure to Volatile
Toxicant by Monitoring
13
For exposure to mixture of toxicants (assuming the
effects are additive), the TWA for mixture is,
n
i i
i
n
ii
mix
TWAC
CTWA
1
1
)(
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Compliance of mixture
(Health risk)
14
For exposure to mixture of toxicants (assuming the
effects are additive)
012
2
1
1 .... n
n
EL
c
EL
c
EL
c
C is the measured 8-hour TWA concentration
EL is the exposure limit for substance (8h)
acceptable risk
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Workers of extended hours (> 8 hour
shift)
Many worker work longer than 8 hour per day or 40 hours per week
Simplest form, dose (concentration x time) is held
constant and new allowable concentration is calculated
Other more complicated adjustment calculations can
account for pharmacokinetic behaviour
XhrallowednewhrELallowed TCTC )()( _8)(
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Example
What is the PEL for benzene over a 12-hour shift given an 8-hour PEL of 1.0ppm?
0.67ppmx
hr) (12
hr) (1.0ppm)(8
)(
)( x
)()(
8
_8)(
allowed
hrallowed
XhrallowednewhrELallowed
C
TCor
TCTC
How to check if the obtained x value is correct? Common sense…
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Another example
Partial period samples
– 4 hours @ 11 ppm, 2 hours @ 14 ppm
TWA calculation
So what is the 8 hours TWA? (answer: 9pm)
12ppmTWA- hour 6
hr 2)(4
m)(2hr)(14ppm)(4hr)(11pp
TWA
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18
CARCINOGEN
Category:
A1: Confirmed human carcinogen
A2: Suspected human carcinogen
A3: Confirmed animal carcinogen with unknown relevance to humans
A4: Not classifiable as a human carcinogen
A5: Not suspected as a human carcinogen
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19
BIOLOGICAL STANDARD
Analysis of substances that do not change in body tissues
– Analysis for metabolite (from metabolism process)
– Analysis of variation of enzyme or biochemical levels
Biological Exposure Indices (BEI)
– Measurement of chemical determinant in a biological media
– Examples • Acetone in urine
• S-Phenylmercapturic acid (metabolite of benzene) in urine
• n-Hexane in end-exhaled air
• Lead in blood
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20
Occupational Standard of
Exposure in Malaysia
AKTA KILANG & JENTERA 1967 – Peraturan-Peraturan Kilang dan Jentera (Timah Hitam)
1984 – Peraturan-Peraturan Kilang dan Jentera (Proses Asbestos)
1986 – Peraturan-Peraturan Kilang dan Jentera (Habuk Galian)
1989 – Peraturan-Peraturan Kilang dan Jentera (Pendedahan
Bising) 1989
AKTA KESELAMATAN & KESIHATAN PEKERJAAN 1994 – Peraturan-Peraturan Keselamatan dan Kesihatan
Pekerjaan (Penggunaan & Standard Pendedahan Kepada Bahan Kimia Berbahaya Kepada Kesihatan) 2000
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Adjustments of PEL
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Adjustments of PEL
Mathematically, correction can be made, thus requiring lower PEL (stricter)
Medical supervision during early adjustment use advisable
Should not be used to justify very high exposures as “allowable” even though exposure periods are short
Adjustments do not have the benefit of historical use and long term observation (no previous exposure data)
Apply adjustments to Exposure Limits with caution because the dose/effect relationship is not linear