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7/31/2019 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
Threshold Limit Values
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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 .
Threshold Limit Values
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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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THRESHOLD LIMIT VALUES
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.
Threshold Limit Values
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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.
THRESHOLD LIMIT VALUES
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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
Design by S chaudhary