Significance of Threshold Limit Values

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SIGNIFICANCE OF THRESHOLD

LIMIT VALUES

Dr.D.J.PARIKH,

Environmental Hygiene/ Monitoring,

NIOH ,Ahmendabad,

Gujarat...


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Threshold Limit Values and its

Significance One of the concepts is that the TLV

for a toxic substance below which

there is no likelihood of any workerexposed to the contaminant beingharmed.Thus the use of TLV serves

the end purpose of protecting a largemajority of workers from healthhazards.


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Threshold Limit Values

The concept is similar to the inoculationprogramme against communicable

disease in public health If TLV is used intelligently in practice the

end purpose of occupational health ofprotecting a large majority of workers

from health hazards can be achieved .


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INDUSTRIAL HYGIENISTS HAVESOUGHT TO ESTABLISH,ADOPT

AND ENFORCE SAFECONCENTRAION LEVELS FOR THEVARIOUS TOXIC CONTAMINANTS

LIKELY TO BE ENCOUNTEREDOCCUPATIONALLY



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Maximum Permissible Concentration(MPC.)

Maximum Allowable/ Admissible orAcceptable Concentration (MAC)

Threshold Limit Value (TLV)

Maximum Permissible Limit (MPL)

Ceiling Limit (C)

..

DIFFERENT NAMES OF TLV


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(A) Airborne concentration of toxic substancerepresenting condition under which it is believed that

all workers exposed repeatedly for 8 hours daily of a40 hours week would not suffer any adverse effectsduring their working life or subsequently.

(B) Airborne concentration of toxic substance at which

neither direct or indirect behavioral and neurotoxineffects, including alteration or reflexes, or adaptive orprotective reaction are detectable.

According to the definition (A) are practical andrealistic, whereas those according (B) represent anideal desirable goal.

USA and Western European Countries =(A)

USSR and East European Countries = (B).

DEFINITION


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SOVIET VALUES ARE CEILING LIMITS ATANY ONE TIME AND ARE THEREFORE MORE

RIGOUROUS IN PRACTICE U.S TLVs ARE BASED ON TIME

WEIGHTED AVERAGE CONCENTRATION FOR

8 HOURS SHIFT AND 40 HOURS

(C)


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BEST AVAILABLE

INFORMATION

PERTAINING TO

TOXIC SUBSTANCE

INDUSTRIAL

EXPERIENCE

EXPERIMENTAL

STUDIES ON

HUMAN

VOLUNTEERS AND

ANIMALS

COMBINAT

ION

OF THREE

TLVs ARE BASED


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TLV ARE BASED ON :

Information pertaining to the toxic

substance

From Industrial Experience

Experimental Studies on Human andAnimal

A combination of the three .



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THRESHOLD LIMIT VALUES

TLV is based on the basis of a NORMAL

Work day

Exposure may differ depending upon : Production Rate

Use of the Substance

Climatic Conditions Intensity of Work


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Workers who breathe through their

mouth ,rather than nose may be exposed tohigher concentration of contaminants

Lung ventilation rate may increase if :-

The nature of work is heavy

Work requires a high metabolic work rate

The work-conditions are hot or humid

Work is performed at altitude


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The American Conference of GovernmentIndustrial Hygienists is an organization

devoted to the administrative andtechnical aspects of occupation andenvironmental health .The association hascontribution to the development of worker

health protection .The conference is aprofessional society,not a governmentagency .

A.C.G.I.H


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THE THRESHOLD LIMIT VALUES (TLVS) ANDBIOLOGICAL EXPOSURE INDICES (BEIS) AREDEVELOPED AS GUIDELINES TO ASSIST IN THECONTROL OF HEALTH HAZARDS.

THESE RECOMMENDATIONS OR GUIDELINE AREINTENDED FOR USE IN THE PRACTICE OF INDUSTRIAL

HYGIENE, TO BE INTERPRETED AND APPLIED ONLY BY APERSON TRAINED IN THIS DISCIPLINE .

THEY ARE NOT DEVELOPMENT FOR USE AS LEGALSTANDARDS,ACGIH DOES NOT ADVOCATE THEIR USE

AS SUCH.

POLICY STATEMENT ON THE

USES OF TLVs AND BELs


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U.S.A: TLVs are incorporated inlegislation by the OSHA

INDIA : TLVS are adopted orrecommended officially by GOVTAgencies

OTHER COUNTRIES : Voluntarycompliance is expected.



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AMENDED FACTORIES ACT 1987,SECTION 41-FCOVERS PERMISSIBLE LIMITS OF EXPOSURE OFCHEMICALS AND TOXIC SUBSTANCES AND THESECOND SCHEDULE PRESCRIBING SUCH LIMITS

FOR 117 CHEMICALS WERE ALSO ADDED. IN U.S.A THE TLVs ARE INCORPORATION INLEGISLATION BY THE OCCUPATIONAL SAFETYAND HEALTH ADMINISTRATION (OSHA).THEY ARE

NOT LEGALLY DEFINED VALUES BUT REPRESENTLEVELS FOR GOODS WORK PRACTICE.


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TLVs ARE AT BEST ESTIMATES

ARRIVED AT THROUGH EDUCATEDGUESS AND INCORPORATION AFACTOR OF SAFETY, WHICH MAY

VARY DEPENDING ON THEINHERENT TOXICITY OF THESUBSTANCE.


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TLV should be used as guideline in thecontrol of health hazards and should not be

used as a dividing line between safe anddangerous concentration .

They are not a relative index of the hazards,

a criteria of air pollution or nuisance, anestimate of toxic potential of interruptedexposure or a proof of an existing diseasesor physical condition.



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Time- Weighted Average: The time-weighed average concentration for anormal 8-hour workday and a 40-hourworkweek,to which nearly all workers

may be repeatedly exposed, day by day,without adverse effect.

DEFINITION OF

TIME-WEIGHTED AVERAGE

CONCENTRATION


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Short Term Exposure Limit (TLV-STEL)

The concentration to which workers can

be exposed continuously for a shortperiod of time without suffering from

(1) Irritation

(2) Chronic or Irreversible tissue damage

(3) Narcosis of sufficient degree toincrease injury,impair self-rescue ormaterially reduce work efficiency , andprovide that the daily TLV-TWA is not

exceeded.

SHORT TERM EXPOSURE LIMIT

(TLV-STEL)


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The concentration that shouldnot be exceeded during any partof the working exposure.

CEILING(TLV-C)


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STELs are recommended only when toxiceffects have been reported from high

short-term exposures in either humans oranimals.A STEL is defined as a 15-minuteTWA exposure which should not be

exceeded at any time during workday evenif the 8-hour TWA is within the TLV-TWA.

STEL-TLV


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THE CONCENTRATION THAT SHOULD NOT BEEXCEEDED DURING ANY PART OF THE

WORKING EXPOSURE.IN CONVENTIONAL INDUSTRIAL HYGIENEPRACTICE IF INSTANTANEOUS MONITORINGIS NOT FEASIBLE, THEN THE TLV-C CAN BEASSESSED BY SAMPLING OVER A 15- MINIUTEPERIOD EXCEPT FOR THESE SUBSTANCESTHAT MAY CAUSE IMMEDIATE IRRITATION

WHEN EXPOSURES ARE SHORT.

THRESHOLD LIMIT VALUE CEILING (TLV-C)


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TLV in mg/m3=

(TLV in ppm)(Gram Molecular W eight of Substance)24.45

TLV in ppm = (TLV in mg/m

3

)(24.45)( Gram Molecular Weight Of Substance)

Conversion of TLVs in ppm to

mg/m3


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BELs are reference values intended asguidelines for the evaluation of potential

health hazards in the practice of industrialhygiene

BELs apply for eight hour exposures,fivedays a week.

BELs are not intended for use as ameasure of adverse effects or fordiagnosis of occupational illness.

BIOLOGICAL EXPOSURE INDICES

(BELs)


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(1)Rational Approach to setting communitair quantity standards to protect notonly population at large,but alsoanimals life, vegetation and structure a

necessary .(2)Occupation T.L.V is reduced by a factor

of 10,25,50 or 100 depending upon the

toxicity of substance.


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DIFFERENCE BETWEEN

OCCUPATIONAL ANDCOMMUNITY EXPOSURES

(A)Duration of Exposure

(B)Concentration levels

(C)Nature of pollutants(D)Controlmeasures


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TOXIC AGENT SOURCE OF

DETERMINATION

NORMAL

VALUES

BIOLOGICAL TLV

Metals

Arsenic As in Urine 0-59 l/l 30l/l

Cadmium Cd in Blood 0-.5 l/dl 2l/dl

Cd in Urine 0- 3 l/l 10 l/l

Lead Pb in Blood 0-20l/dl 60l/dl

ALA dehydratasein Blood

1500-500U/l ---

ALA in Urine 1-9 mg/l 15mg/l

Coprophorphyrine inUrine 0-100 l/l 500l/l

Recommendation for biological TLVs

TOXIC SOUREC OF NORMAL BIOLOGICAL TLV


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TOXICAGENT

SOUREC OFDETERMINA-TION

NORMALVALUE

BIOLOGICAL TLV

Mercury Hg in Blood 0-1l/dl 3.5l/dl

Hg in Urine 0-20l/l 100l/l

Selenium Se in Urine ------- 100l/l

Vanadium V in Urine 0-20l/l 30l/l

SOLVENTS

Benzene Phenols in Urine 1-10mg/l 40mg/lPerchieroethylene

Perchieroethylene inBlood

0 70l/dl

Styrene Mandelic Acid in Urine 0 2000mg/l

Toluene Hippuric Acid in Urine 500- 3000mg/l


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FORMULAE APPLY ONLY WHEN THE COMPONENTS IN A MIXTUREHAVE SIMILAR TOXICOLOGICAL EFFECTS :

C1 +C2 + C3 + . = 1

T1 T2 T3

C= CONCENTRATION IN AIR

T= TLV OF THE SUBSTANCE

EXAMPLE :

AIR CONTAINS 400 ppm OF ACETONE (TLV =750 ppm ) ,150 ppm OFSEC-BUTYL ACETATE (TLV = 200 ppm ) , AND 100 ppm OF METHYLETHYL KETONE (TLV= 200ppm )

400 + 150 + 100 = 0.53 +0.75 +0.5 = 1.78

750 200 200

THRESHOLD LIMIT VALUES IS EXCEEDED

T.L.V FOR MIXTURES


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THANK YOU

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Significance of Threshold Limit Values

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