Rules of Thumb

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E U iExposure Unit

hThe exposure assessment process is performed independently on each physical hazard, chemical or chemical mixture in the ,SEG. Each chemical - SEG combination is referred to as a exposure unit (EU).

The product of the exposure assessment process is to classify exposures into ranges ( b d ) d t(exposure bands) as compared to an occupational exposure limit.

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E B dExposure BandsExposure Relationship to the OEL (95th Percentile)Exposure Rating

Relationship to the OEL (95 Percentile)

0 X0.95 ≤ 0.01 x Exposure Limit (OEL)

1 0.01 x OEL < X0.95 ≤ 0.1 x OEL2 0.1 x 0EL < X0.95 ≤ 0.5 x OEL3 0 5 x OEL < X ≤ OEL3 0.5 x OEL < X0.95 ≤ OEL4 1 x OEL < X0.95 ≤ 2 x OEL5 2 x OEL < X0.95 ≤ 5 x OEL6 5 x OEL < X0.95 ≤ 10 x OEL

7 10 x OEL < X0.95 ≤ 50 x OEL8 X > 50 OEL

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8 X0.95 > 50 x OEL

T f I h l i H dTypes of Inhalation Hazards

VaporsVaporsGasesFumesFumes MistsA lAerosolsParticulates

T t lTotal Respirable fractions

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F d C di iForm and Conditions

Pure materialMixtureSolubilitySuspendedTemperature

Air Material

Pressure

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M h i f I d iMechanism for Introduction

EvaporationSublimationDecompositionGeneration via chemical reactionVaporization (heat to a point above boiling point - e.g., welding fume)Mechanically generated – e.g., spraying or agitation

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V PVapor PressureVapor pressure is the pressureexerted by the

h f t h /li idgaseous phase of a two phase—gas/liquid or gas/solid system.The pressure of the vapor that is formed above its li id lid i ll d thliquid or solid is called the vapor pressure. If a substance is in an enclosed place the two phase system will arrive at an equilibrium state. h l b d b l dThis equilibrium state is a dynamic, balanced

condition with no change of either phase. For a specific temperature, the pressure of the vapor measured at equilibrium state is the equilibrium ormeasured at equilibrium state is the equilibrium or saturated vapor pressure. This pressure is a fraction of the total pressure, which is equal to 760 mm Hg at sea level

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which is equal to 760 mm Hg at sea level.

V PVapor PressureAn agents vapor pressure at it’s boiling point is 760

f H ( t h i )mm of Hg (atmospheric pressure)The vapor of specific agents in mixtures is lower than the agent’s vapor pressure in its pure state.Vapor pressure changes (increases) with temperature.Vapor pressures and boiling reports are usually

d l bl d dreported on MSDS or are available in standard sources (e.g., TOXNET – HSDB, NIOSH Pocket Guide)For comparison vapor pressures must use some

bl t t ( ll 25 d C)comparable temperature (usually 25 degrees C)

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E P i l V R l f 10Exposure Potential Vapors: Rule-of-10

Level of Control Fraction of SaturationLevel of Control Fraction of Saturation

Confined Space –Virtually no circulation

1/10th of SaturationVirtually no circulationPoor – Limited Circulation

1/ 100th of SaturationCirculationGood – General ~ 6 air turnovers/hr

1/1,000th of Saturation 6 air turnovers/hr

Capture 1/10,000th of Saturation

Containment 1/100 000 of Saturation

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Containment 1/100,000 of Saturation

E lExample

Benzene has a saturated vapor pressure at 25°C of 95.2 mm of Hg and atmospheric pressure is 760 mm of Hg. The saturated vapor pressure (VP) of benzene at 25°C is calculated in the following manner:

Saturated VP of Benzene =Saturated VP of Benzene = (95.2 mm of Hg/760 mm of Hg) * 1,000, 000

= 125,000 ppm benzeneIf benzene were used in a room with only good general ventilation, exposures would be expected on the order of 125 ppm, a level ~ 100 times its OEL.

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o 5 pp , a e e 00 t es ts O

B E lBenzene Example

Most IH’s who have worked with exposure scenarios associated with benzene know that b i t i t i ibenzene requires containment engineering controls to reduce exposures to the order of magnitude of the 0 5 ppm TLVmagnitude of the 0.5 ppm TLV.

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Vapor Pressure Changesi h Twith Temperature

The vapor pressure increases with the temperature of the liquid rather than ambient temperaturetemperature.Vapor pressure at temperatures other than ambient (25 degrees C) can be found in( g )

Standard chemistry textsCalculated using

A t i ’ E tiAntoine’s Equation Clausius-Clapeyron Equation

Estimated with a rule-of-thumb

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Calculate Vapor Pressure Using A t i ’ E tiAntoine’s Equation

log10(p) = A - (B / (t + C))

Where:p = vapor pressure (mm of Hg)

( 0)t = temperature (C0)A, B & C are constants unique to each h i lchemical

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Cl i Cl E tiClausius-Clapeyron Equation

Plot Log10(p) vs. 1/TLog10(p) = m(1/T) + C

Where:p = vapor pressure in mm of HgT = temperature in degrees Absolute (K)T temperature in degrees Absolute (K)

m = slope of the linec = intercept of the line

Note: At the BP, the VP=760. If the vapor pressure of one more point is known, the vapor pressure at any temperature can be calculated

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Estimated of Vapor Pressure with a l f h brule-of-thumb

The vapor pressure (VP) of the chemical will approximate double with each 10°C increase i t t f th li idin temperature of the liquid.

For example, if the VP of a chemical is 25 mm of Hg at 25°C its VP at 35°C will beof Hg at 25°C, its VP at 35°C will be approximately 50 mm of Hg and at 45°C approximately 100 mm of Hgapproximately 100 mm of Hg

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D fi i i f V H d R iDefinition of Vapor Hazard Ratio

Vapor Hazard Ratio (VHR) - The measure of a PURE material’s ability to volatilize ( d ) di id d b(expressed as vapor pressure) divided by the material’s Occupational Exposure Level (OEL)Level (OEL).

VHRVHR = vapor pressureOEL

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R fReference

Popendorf, W., Vapor Pressure and Solvent Vapor Hazards. Am. IND. Hyg. A J 45(10) 719 726 (1984)Assoc. J. 45(10): 719-726 (1984)

Note:Reference also defines the term Vapor H d I d (VHI) th l (VHR)Hazard Index (VHI) as the log (VHR)Reference does not address mixtures

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U f V H d R iUse of Vapor Hazard Ratio

If two chemicals have the same VHR, they will require the same level of control to assure exposures are not excessive. The VHR is the Rosetta Stone of IH

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V H d R i S lVapor Hazard Ratio Scale

Vapor Pressure (mm of Hg)/ OEL (ppm)

Vapor HazardRatio Scale

0 05 1< 0.05 1

0.05 to < 1 21 to < 25 31 to < 25 3

25 to < 500 4500 to < 3000 5500 to < 3000 5

> 3000 6

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Chemicals in the same Vapor Hazard R i CRatio Category

S l S lScale - 1 cyclohexanolbiphenyl

Scale - 4ammoniabenzene p y

Scale - 2acetoneaniline

Scale - 5ethylene oxidemethyl mercaptananiline

Scale - 3toluene - 2,4 -diisocyanate (TDI)

methyl mercaptanScale - 6

chlorine hdiisocyanate (TDI)

n - hexanephosgene

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V H d R i C lVapor Hazard Ratio - ControlsVapor Pressure Vapor Required Levels of Control

(mm of Hg)/ OEL (ppm)

HazardRatio Scale

< 0.05 1 General Ventilation ~ 3 to 6 air< 0.05 1 General Ventilation 3 to 6 air turnovers /hr

0.05 to < 1 2 Good general ventilation ~ 6 to 12 air turnovers/hr (GGV)turnovers/hr (GGV)

1 to < 25 3 GGV with capture at emission points

25 to < 500 4 Capture at points of emission with containment wherever practical

500 to < 3000 5 Containment

> 3000 6 Primary and Secondary Containment

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> 3000 6 Primary and Secondary Containment

E lExamplesMEK has a VP = 86.7 mm of Hg and an OEL of 200 ppm, g pp ,VHR = 0.42 – requires good general ventilation ~ 6 to 12 air turnovers/hr (GGV)Methylene chloride has a VP = 430 mm of Hg and an OEL of 25 ppm VHR 17 2 requires GGV with capture atof 25 ppm, VHR = 17.2 – requires GGV with capture at emission pointsHexachlorocyclopentadiene(C56) has a VP= 0.06 mm of HG and an OEL of 0.01 ppm, VHR = 6 – requires GGVHG and an OEL of 0.01 ppm, VHR 6 requires GGV with capture at emission pointsBenzene has a VP = 95.2 mm of Hg and an OEL of 0.5 ppm, VHR=190.4 - Capture at points of emission with

t i t h ti lcontainment wherever practical

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E lExamplesIf a plant would like to purchase cyclohexane for aIf a plant would like to purchase cyclohexane for a process at 25°C. Cyclohexane’s VP = 96.0 and its OEL is 100 ppm. The process ventilation is at scale 3 (GGV ith t t i i i t ) Will(GGV with capture at emission points). Will exposures be acceptable? The VHR = 0.96 which on the border between scale 2 and 3. Controls are adequate and the exposure band will likely be 2.

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E lExamplesAssume that the plant has a good exposure assessment p g pillustrating that the cyclohexane exposure is 25 ppm or exposure band 2. If the plant would like to use MEK in the process, what would be MEK’s exposure level and what would be its exposure band. Note that MEK’s VHR=0.42, meaning that p gthe controls would be more than adequate for MEK. The likely MEK exposure can be estimated by the following equation:

MEK Exposure = [VHR / VHR ] x [Cyclo Exposure/OEL ]MEK Exposure = [VHRMEK / VHRCyclo] x [Cyclo Exposure/OELCyclo] x OELMEK

The cyclohexane exposure is currently 25% of its OEL and h f h [ 2/ ] 2 2therefore the MEK exposure = [0.42/0.96] x 0.25 x 200 ppm =

22 ppm. MEK exposures would be at the low end of exposure band 2.

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P i l F d MiParticulates, Fumes and Mists

Define a Potential Hazard Ratio analogous to the VHR.

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Potential Hazard Ratio Scale for S lid d MiSolids and Mists

Particle sizeParticle densityParticle density Drop sizeStratification by OELStratification by OEL

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P i l H d R iPotential Hazard Ratio

OEL Range(mg/m3)

Potential HazardRatio (PHR) Scale

> 5 1

≤ 5 to 1 2≤ 5 to 1 2

≤ 1 to 0.1 3

≤ 0 1 t 0 01 4≤ 0.1 to 0.01 4

≤ 0.01 to 0.001 5

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≤ 0.001 6

P i l H d R i C lPotential Hazard Ratio - ControlsOEL Range Potential Required Levels of Control(mg/m3) Hazard

Ratio Scale> 5 1 General ventilation> 5 1 General ventilation

~ 2 to 4 air turnovers/hr ≤ 5 to 1 2 Good – General + fans

4 t 6 i t /h~ 4 to 6 air turnovers/hr ≤ 1 to 0.1 3 Good – General + fans

~ 6 to 8 air turnovers/hr≤ 0.1 to 0.01 4 Capture

≤ 0.01 to 0.001 5 Containment

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≤ 0.001 6 Secondary containment

R l f Th b D iRule of Thumb - Dustiness

If particles are very small (high degree of dustiness), increase the PHR scale by 1. For example, if an chemical agent has an OEL of 0 5 mg/m3 (PHR Scalechemical agent has an OEL of 0.5 mg/m3 (PHR Scale 3) and is dusty, increase the expected controls to a PHR Scale 4.

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Using Determinants of Exposure to D i E B dDetermine Exposure Band

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D i f EDeterminants of ExposureEnvironmental determinants:Environmental determinants:

Type of controlEfficiency of controlEfficiency of control

Canopy hood vs. laboratory hood

Frequency and duration of exposureFrequency and duration of exposureDistance form sourceSize of container openingSize of container openingSurface area

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D i f EDeterminants of Exposure

Agent Determinants:Agent surface areagVapor hazard indexCompositionpQuantity of agent Absorption rateAbsorption rateApplication method

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Identify Determinant RatingS l U i S ifi d D fi i iScale Using Specified Definitions

Exposure ControlExposure ControlFrequency and DurationVapor Hazard Ratio

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C l R i S l D fi i iControl Rating Scale DefinitionsScale ESTIMATION OF OVERALL LEVEL OF CONTROLScale ESTIMATION OF OVERALL LEVEL OF CONTROL

(Circle)

0 Closed system; no potential for release to work area

1 Primarily closed systems with effective engineering controls1 Primarily closed systems with effective engineering controls are in place to control exposure at potential contact points.

2 Open system; effective engineering controls in place to contain/remove airborne contaminants from work environment.

3 Combination open and closed system; a combination of engineering and administrative controls in place to control exposures

4 Open system; ineffective or no engineering controls in place

5 Open system; no program in place to minimize worker

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exposures; visual airborne contaminants, odors or sensory response indicate potential exposure exists

Frequency and Duration Scale D fi i i

Scale ESTIMATION OF OVERALL FREQUENCY (Circle)

DefinitionsScale ESTIMATION OF OVERALL FREQUENCY (Circle)1 Stressor is present less than 1 day/month; or less than 5

minutes/day 2 Stressor is present at least one day per month as follows: for 82 Stressor is present at least one day per month as follows: for 8

hour shifts, 5 minutes to 1 hour/day; for 12 hour shifts, 5 minutes to 1.5 hours/day

3 Stressor is typically present; for 8 hour shifts, 1 to 2 hours/day; f 12 h hift 1 5 t 3 h /dfor 12 hour shifts, 1.5 to 3 hours/day

4 Stressor is typically present; for 8 hour shifts, 2 to 4 hours/day; for 12 hour shifts, 3 to 6 hours/day

5 for 8 hour shifts, 4 to 8 hours/day;5 for 8 hour shifts, 4 to 8 hours/day; for 12 hour shifts, 6 to 12 hours/day

STEL Identify tasks that are conducted infrequently such as less than one day/month

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Vapor Hazard Ratio (VHR)S l D fi i iScale Definitions

Vapor Vapor Pressure ( mm ofVapor Hazard Index Scale

Vapor Pressure ( mm of Hg, @ 25C) / OEL (ppm)

Scale 1 < 0.05 2 0.05 - < 13 1 - < 254 25 - < 5005 500 – 30006 > 3000

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E R ti E ti tiExposure Rating Estimation

Exposure Rating Estimation (ERE) =(C l i )(Control Rating) X (Frequency and Duration Rating) X(Vapor Hazard Index Rating)

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D i E R i B dDetermine Exposure Rating or Band

Exposure Rating Estimation (ERE)

Exposure Rating (ER)

<20 0

20 – 40 1 20 40 1

40 – 60 2

60 80 3 60 – 80 3

>80 4

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Exposure RatingExposure Rating(Note: This rating system is not AIHA’s)

Exposure Rating

Statistical Interpretation

0 X0.95 ≤ 0.1 x Exposure Limit (EL)

1 0.1 x EL < X0.95 ≤ 0.25 x EL2 0.25 x EL < X0.95 ≤ 0.5 x EL3 0.5 x EL < X0 95 ≤ EL3 0 5 0.95

4 X0.95 > EL

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E lExampleAssume the following mixture:g

Chemical Weight %

OEL (ppm)

Molecular Weight (MW)

Pure Vapor Pressure (VP) in torr at 25°C

T l (T l) 40 20 92 1 28 4Toluene (Tol) 40 20 92.1 28.4

Xylene (Xy) 20 100 106.2 8.74

ethyl acetate (EA) 20 400 88.1 93.2

Benzene (BZ) 2 0.5 78.1 94.8

methylene chloride 3 25 84 9 435methylene chloride (MeCl)

3 25 84.9 435

Carbon tetrachloride (CCl4)

15 5 153.0 115

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tetrachloride (CCl4)

C lli CControlling Component

Which component is controlling? That is, in this mixture which component has the highest potential to exceed its’ corresponding OEL.

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E lExampleAssume the following mixture:g

Chemical Weight %

OEL (ppm)

Molecular Weight (MW)

Pure Vapor Pressure (VP) in torr at 25°C

T l (T l) 40 20 92 1 28 4Toluene (Tol) 40 20 92.1 28.4

Xylene (Xy) 20 100 106.2 8.74

ethyl acetate (EA) 20 400 88.1 93.2

Benzene (BZ) 2 0.5 78.1 94.8

methylene chloride 3 25 84 9 435methylene chloride (MeCl)

3 25 84.9 435

Carbon tetrachloride (CCl4)

15 5 153.0 115

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tetrachloride (CCl4)

C l l iCalculationsA B C D E F G H I A B C D E F G H I

Chemical WT %

OEL (ppm)

MW VP

Mole Fraction

Mole % CorrectedVP

PHR PHR Norm.

(A/C) (E/ Total E) (F x D) (G/B) (H/ Largest H) x 100H) x 100

Tol 40 20 92.1 28.4 0.434 0.43 12.2 0.611 12.70% Xy 20 100 106.2 8.74 0.188 0.187 1.63 0.016 0.34 EA 20 400 88 1 93 2 0 227 0 225 20 9 0 052 1 09EA 20 400 88.1 93.2 0.227 0.225 20.9 0.052 1.09Bz 2 0.5 78.1 94.8 0.026 0.026 2.41 4.814 100.00 MeCl 3 25 84.9 435 0.035 0.035 15.2 0.610 12.66 CCl4 15 5 153 0 115 0 098 0 097 11 2 2 236 46 44CCl4 15 5 153.0 115 0.098 0.097 11.2 2.236 46.44 Total: 100 1.009 1.00

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Why Do We Need Rules-of-Thumb?

Consider the following cases.

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S iScenarioA plant uses high purity toluene as a solvent in a

th t i l 35 k It i 4 30process that involves 35 workers. It is 4:30 pm on a Friday afternoon and you, the IH, and your family will be leaving on a week long vacation at the shore early the next morning You must leave the plant no laterthe next morning. You must leave the plant no later than 5:00 pm and you have another 3 or 4 items on your task list that have to be complete before you leave. A process engineer comes into your office andleave. A process engineer comes into your office and asked you to sign off on using a lower grade of toluene that contains up to 1% benzene. Using this lower grade of toluene will save the plant $250 000/ Th ti d t t h l d$250,000/yr. The operations department has already concluded that the lower grade toluene is acceptable and the safety and environmental departs have also already signed off on the change

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already signed off on the change.

S iScenario

The engineer indicates that he realizes that the OSHA hazard communication and benzene standards will require some new labels and that the workers will have to be trained and that these requirements will be completed prior to receiving the new material in the plant. The plant will need to order a shipment no p p plate than Saturday.

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S iScenario

C l h l i i d bi hl d hCurrently, the toluene is monitored bimonthly and the data collected over the last year indicates the exposure is 9.5 ppm (95th percentile, GM=2.10, GSD=2.5, N=6).

Pertinent information:Toluene’s TLV = 20 ppm, BP=110.6°C, VP=28.44 mm of Hg MW 92 1of Hg, MW=92.1

Benzene’s TLV = 0.5 ppm, BP=80.1°C, VP=95.18 mm of Hg MW 78 1Hg, MW=78.1

Do you sign off on the change?

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The vapor hazard ratio (VHR) of toluene i 28 4 f H / 20 1 42is 28.4 mm of Hg / 20 ppm = 1.42.

The vapor pressure of benzene is suppressed because it is a small ppcomponent of a mixture but the corrected vapor pressure can be p pcalculated using Raoults law. Therefore the VHR for benzene = 1.12Therefore the VHR for benzene 1.12 mm of Hg / 0.5 ppm = 2.24.

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VHRbz / VHRtol = 2.24/1.12 = 1.58

Currently toluene exposures are 9.5 y pppm/20 ppm = 47.5 % of the OEL

Benzene exposures will = 1.58 X 47.55% of it corresponding OEL of 0 5 ppmof it corresponding OEL of 0.5 ppm

Therefore benzene exposures can be expected to = 1.58 X 0.475 X 0.5 = 0.38 ppm.

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Although this value is below the benzene TLV it is above the action level which usually triggers medicalabove the action level which usually triggers medical surveillance requirements along with other requirements.

It would be my recommendation as an IH to not approve the use of toluene with 1% benzene Aapprove the use of toluene with 1% benzene. A known human carcinogen would be introduced into the workplace where a significant number of employees

ld b ff t d t i ifi t l l fwould be affected, at a significant level of exposure and there would likely be a series of other costs that would have a negative impact on the projected savings.

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