ACGIHACGIH®® TLVs TLVs®® for for Physical Agents Physical Agents

Committee UpdateCommittee Update

Vice-Chair: Thomas BernardUniversity of South Florida College of Public Health

TLVTLV®®

Physical Agents CommitteePhysical Agents Committee

Process for Hazardous Agent Selection and Decision Making

MissionMission

To foster, solicit, collect and evaluate data on potential health hazards of exposures to physical agents. When appropriate, recommend ACGIH® Threshold Limit Values® for physical agents.

2002 PAC2002 PAC

Harry MaharMaurice BitranThomas BernardGerald ColesAnthony CullenDaniel JohnsonJohn LeonowichWilliam MurrayBhawani Pathak

Robert Patterson

Thomas TenfordeCarla Treadwell

Consultants:Thomas AdamsThomas ArmstrongGregory LotzMartin MainsterGary Myers

OverviewOverview

• Physical Agents

• Process– Committee Activities– TLV® Development

• Future– Format– Agents

DisclaimerDisclaimer

The opinions expressed here are those of the author

and not ofhis employer,

the Physical Agents Committee or

the ACGIH® Worldwide.

Physical AgentsPhysical Agents

It’s the Movement of Energy

Risk of Health Risk of Health EffectsEffects

• What is the nature of the energy?

• How much energy?

• What is the interaction with tissue?

Nature of EnergyNature of Energy

• Electric and Magnetic Fields

• Photons

• Kinetic Energy– Pressure– Vibration– Mechanical

• Heat

Amount of EnergyAmount of Energy

• Total Amount of Energy Absorbed– What does it take to raise water temperature?

• Rate of Absorption (Power or Intensity)– How fast does the temperature rise?

• Normalized to Surface Area(e.g., mJ/cm2, mW/cm2)

InteractionsInteractions

• Electric and Magnetic Fields– Induce Currents– Align Molecules– Vibrate Molecular Bonds

• Photons– Vibrate Molecular Bonds– Disrupt Molecular Bonds

More InteractionsMore Interactions

• Mechanical Disruption of Tissue– Pressure– Vibration– Force Applications

• Loss of Tissue Function– Thermal: Gain or Loss of Heat

Bernard Watt-O-MeterBernard Watt-O-Meter

Power Limits for Various Exposures [mW/cm2]

Electric and Magnetic Fields 170,000 Radiofrequency/Microwave 1.0

Infrared Light 10Blue Light 0.0001

Ultraviolet Light 0.0012 Ionizing Radiation 0.00000003

Noise 0.00003Heat Stress 30

{Not Accepted, or Considered Acceptable, by Any Authority}

ExposureExposure

• Energy Distribution in the Immediate Environment

• The distribution is usually described as Power or Intensity (directly or through a surrogate) versus Frequency or Wavelength in Bands

Exposure ThresholdExposure Threshold

• Total Energy– Ability to Absorb Energy

• Rate of Energy (Power or Intensity)– Ability to Dissipate Absorbed Energy

In a Band

Integrated Over All Bands

ProcessProcess

Committee ActivitiesDevelopment of TLVs®

RepresentationRepresentation

• Usually one or two members with an expertise for a particular agent (e.g., a small portion of the electromagnetic spectrum)

• Small committee to maintain a working and collegial group. We meet as a whole.

• Leverage with outside experts

Updating TLVsUpdating TLVs®®

• PAC meets with outside experts

• Members bring recommendations to the PAC for discussion

• Consideration of actions taken by national and international committees or agencies

New TLVsNew TLVs®®

• Quintessential Example: Hand Activity

• Formed a cadre of consultants• Convened a conference• Developed recommendation and Documentation

• Presented to PAC and discussed• PAC voted after internal deliberations

FutureFuture

Format

Agents

FormatFormat

• TLV® Book– Use of Flow Charts– Evolving (see Heat Stress and RF/MW)

• Training• Documentation

– Expanded and Focused (see HAL and Lifting)

– Health Effects and Exposure Indices– Guidance (see Heat Stress)

FormForm

• Physical agents have their own history and character with respect to measurement and exposure assessment

• There is an underlying similarity among the physical agents that may be introduced

Example SetExample Set

• Radiofrequency / Microwave Radiation

• Optical Radiation (IR, Visible and UV)

• Vibration (Hand-Arm and Whole Body)

• Noise

Energy DistributionEnergy Distribution

0.01

0.1

1

10

100

1000

0.001 0.01 0.1 1 10 100 1000

Ene

rgy

Bands

Energy Limits Energy Limits Within BandsWithin Bands

1

10

100

1000

10000

100000

1000000

0.001 0.01 0.1 1 10 100 1000

Ene

rgy

Lim

it

Bands

Emin

Limits by BandLimits by Band

Is the limit exceeded within one or more bands?

0.01

0.1

1

10

100

1000

10000

100000

1000000

0.001 0.01 0.1 1 10 100 1000

Ene

rgy

Bands

PD Exp Lmt

Sensitivity CurveSensitivity Curve

Sensitivity = Energy Limit / Emin

0.1

1

10

100

1000

0.001 0.01 0.1 1 10 100 1000

Sen

sitiv

ity

Bands

Hazard FunctionHazard Function

0.001

0.01

0.1

1

0.001 0.01 0.1 1 10 100 1000

Filt

er M

ultip

lier

Bands

Hazard Function = 1.0 / Sensitivity

Effective ExposureEffective Exposure

0.00001

0.0001

0.001

0.01

0.1

1

10

100

1000

0.001 0.01 0.1 1 10 100 1000

Ene

rgy

Bands

ED E-eff

Effective Exposure = Energy Distribution x Hazard Function

Total EnergyTotal Energy

Multiplying– Energy Limits by Band– Hazard Function by Band

and Integrating (Summing)

Yields a Constant Value:

A Total Energy Limit

Limit by Total Limit by Total EnergyEnergy

Total Energy – In One Band– Under the Effective Energy Curve

Compared to

Total Energy Limit

In SummaryIn Summary

• TLVs®

– Limit Power (Ability to Dissipate)– Limit Total Energy (Ability to Absorb)

• Limit by– Band– Total

Agents Under Agents Under ReviewReview

• Lasers

• Vibration

• Cold Stress

• HAL• Lifting• WMSDs• Wide-Band RF

• Altitude

• Impulse Noise

• ELF H-Fields

Scheduled BreakScheduled Break

Take a minute to stretch!