4-3 Industrial Hygiene

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.

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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



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



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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4-3 Industrial Hygiene

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