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7/30/2019 4-3 Industrial Hygiene
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INDUSTRIAL HYGIENE
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Science devoted to the identification, evaluation andcontrol of occupational conditions that cause sickness
and injury
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IH: IDENTIFICATION
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IH: Identification
Thorough study on:-
Chemical process
Operating conditions
Operating procedures
Source of information:-
Process design description
Operating instructions
Safety reviews
Equipment vendor descriptions
Info from chemical supply
Info from operating personnel
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Potential hazards
Liquids
Vapors
Dusts Fumes
Noise
Radiation
Temperature
Mechanical
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Entry mode of toxicants
Inhalation
Body absorption (skin or eyes)
Ingestion Injection
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Potential damage
Lungs
Ears
Nervous system
Kidneys Circulatory system
Skin
Eyes
Liver
Reproductive organs
Other organs
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Data useful for Health Identification
Threshold limit values (TLV)
Odor threshold for vapors
Physical state
Vapor pressure of liquids
Sensitivity of chemical to temperature or impact
Rates and heats of reaction
Hazardous by-products
Reactivity with other chemicals
Explosive concentrations of chemicals, dusts andvapors
Noise levels of equipment
Types and degree of radiation
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MSDS
Important references used during an IH studyinvolving toxic chemicals
List physical properties of a substance that may berequired to determine potential hazards of thesubstance
Industrial hygienist or safety professional mustinterpret the physical and toxicological propertiesto determine hazard associated with chemicals
MSDS available from;
The chemical manufacturer
Commercial source
Private library developed by the chemical plant
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IH: EVALUATION
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IH: Evaluation
Determine the extent and degree of employeeexposure to toxicants and physical hazards in theworkplace environment
TLV-TWA
Single exposure
Multiple exposure
All monitoring system has drawbacks:
The workers may be move in/out from exposed workplace
Concentration of toxicant may vary at different location inwork area
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THRESHOLD LIMIT
VALUE
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TLV
Refer to airborne concentrations thatcorrespond to condition under which noadverse effects are normally expected duringworkers lifetime.
The body is able to detoxify and eliminate theagent without any detectable effects.
Units:
ppm (by volume), mg/m3,
for dust mg/m3 and mppcf (millions of particles per ft3air)
The TLV assumes that workers are exposed onlyduring normal eight-hour workday
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TLV
The American Conference of Governmental Industrial
Hygienists (ACGIH) established 3 different types of TLV
1. TLV-TWA
2. TLV-STEL
3. TLV-C
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TLV-TWA
Time-weighted average for a normal 8-hour workdayor 40- hour work week, to which nearly all workerscan be exposed, day after day, without adverseeffects.
PEL (Permissible exposure level) defined by OSHA(USA) generally follow closely TLV-TWA
More TLV-TWA data are available than TWA-STEL andTWA-C
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TLV - STEL
Short-term exposure limit. The maximumconcentration to which workers can be exposed fora period of up to 15 minutes continuously withoutsuffering
Intolerable irritation
Chronic or irreversible tissue change
Narcosis of sufficient degree to increase accidentproneness, impair self-rescue, or materially reduce
worker efficiency, provided that no more than 4excursions per day are permitted, with at least 60minutes between exposure periods, and providedthat the daily TLV-TWA is not exceeded
16
17
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TLV-C
Ceiling limit. The concentration that should not beexceeded, even instantaneously.
17
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General Formula for TWA
n
i
i
n
i
ii
t
tc
TWA
1
1
ci is concentration during ith intervalti is duration of the i
th interval
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For workers exposed for more than 8 hour
Since the computation is normalized to 8 hours, ifworkers are exposed to TLV~TWA level for 12continuous hours, then TWA=(12/8)(TWA8)
Thus higher TLV is tolerated ? Think
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8-hour Time Weighted Average
For a worker who works at various locations in theplant, his/her exposure is measured usingintermittent samples at fixed points,
8
)(...)()(1 2
0 00 21
8
t t
n
t n
dttCdttCdttCTWA
8
2211
8
nnctctct
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
14ppmTWAhr2)2(4
ppm)m)(2hr)(20(2hr)(14ppm)(4hr)(11pp
TWA
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Another example
PEL for the chemical involved is 12 ppm
Partial period samples
4 hours @ 11 ppm, 2 hours @ 14 ppm
TWA calculation
12ppmTWA-hour6
hr2)(4
m)(2hr)(14ppm)(4hr)(11pp
TWA
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Another Example
PEL for the chemical involved is 12 ppm
Partial period samples
4 hours @ 11 ppm, 2 hours @ 14 ppm, 2 hour not sampled
TWA calculation
9ppmTWA-hour8
hr2)2(4
)(2hr)(0ppmm)(2hr)(14ppm)(4hr)(11pp
TWA
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TLV FOR MIXTURE
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Evaluation of Exposure to VolatileToxicant by Monitoring
For exposure to mixture of toxicants (assuming theeffects are additive), the TWA for mixture is,
n
i i
i
n
i
i
mix
TWAC
C
TWA
1
1
)(
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Compliance of mixture
For exposure to mixture of toxicants (assuming theeffects are additive)
0.1...2
2
1
1
n
n
TWATLV
c
TWATLV
c
TWATLV
c
C is the measured 8-hour TWA concentrationTLV-TWA is the exposure limit for substance
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TLV FOR MIXTURE EXPOSURE LIMIT FORWORKING GREATER THAN 8 HOURS
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Workers of extended hours
Many worker work longer than 8 hour per day or 40hours per week
Apply adjustments to ELs with caution
Should not be used to justify very high exposures asallowable" where exposure periods are short
Medical supervision during early adjustment
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EL for > 8 hour shift
Simplest form, dose (concentration x time) is heldconstant and new allowable concentration iscalculated
Other more complicated adjustment calculationscan account for pharmacokinetic behaviour
XhrallowedhrallowedTCTC )()(
8
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Example
What is the PEL for benzene over a 12-hour shift givenan 8-hour PEL of 1.0ppm?
0.67ppmxhr)(12
hr)(1.0ppm)(8
)(
)(x
)()(
allowed
hrallowed
Xhrallowedhrallowed
C
TCor
TCTC
8
8
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IH: CONTROL
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Medical test to determine exposurebefore symptoms appear
Compare results with a medical baseline results(usually done on new employees beforeemployment)
Respiratory problem (using spirometer): asthma, bronchitis
Nervous system disorder: mental status, motor system reflexes,sensory system
Skin texture, hair, nail, vascularity (blood vessel)
Blood count (red/white cell, haemoglobin, platelet count)
Kidney (test for quantity and for sugar and proteins in urine)
Liver (through chemical test on urine and blood)
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IH: Control
Control of Exposures: Employ methods to eliminate orreduce exposure resulting in elimination or reductionof the occurrence of occupational disease through:
Engineering (including process) interventions
Administrative/programmatic measures
Personal protective equipment
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IH: Control
Type Typical techniques
Enclosure Enclose hazardous operationsSeal rooms, sewers, ventilation
Local ventilation Use proper designed hoodUse local exhaust at sample point
Dilution ventilation Design ventilation to isolateoperation from rooms and office
Wet methods Clean areas frequently
Use water sprays to shield trenchesor pump seals
Good housekeeping Provide water and steamconnections for area washing
Personal protection Use safety glasses and face shields
Wear appropriate respirator, etc
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IH: Control
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Example of industrial Hygiene Activity
Monitoring toxic airborne concentration
Reducing toxic airborne by using ventilation
Selecting PPE to prevent worker exposure
Developing procedure for handling hazardousmaterial
Any other activity to ensure workers are notexpose to harmful levels
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