Derivation of IDLH Values - Esafetyline - the source for … s/EEI Spring... · 2011-10-25 ·...

Derivation of IDLH Values

G. Scott Dotson, PhD, CIH

CDC/NIOSH/EID

Cincinnati, OH

[email protected]

Disclaimer

The findings and conclusions in this presentation have not been formally disseminated by the National Institute for Occupational Safety and Health (NIOSH) and should not be construed to represent any agency determination or policy.

3

Introduction

• Inhalation of chemicals– Primary exposure pathway within many occupational settings

• Acute or short-term exposures to high concentrations of some airborne chemicals have the ability to quickly overwhelm workers, resulting in a wide spectrum of undesirable health outcomes:

– that may include irritation of the eyes and respiratory tract,

– severe irreversible health effects,

– impairment of the ability to escape from the exposure environment and,

– in extreme cases, death.

4

Introduction

• Within occupational settings, these “high risk” situations are often referred to as Immediately Dangerous to Life or Health (IDLH) environments, atmospheres, conditions or situations

• Dynamic exposure scenarios – Unique– Non-routine

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IDLH Environments

IDLH environments

– Result from both unplanned & planned events

• Fires

• Chemical releases/spills

• Industrial accidents/explosions

• Clandestine drug laboratories

• Terrorist attacks

• Confined space operations

• Non-routine work tasks

IDLH Values

• Established to characterize the toxic effects associated with IDLH environments and identify airborne concentrations that may:

– Impair escape;

– Cause severe irreversible effects; or

– Death

• History

– 1974- Standard Completion Program (SCP)

– 1994 Update

– Present Date6

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IDLH values

• IDLH values are defined as: – “An atmospheric concentration of any toxic, corrosive

or asphyxiant substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual’s ability to escape from a dangerous

atmosphere” (29 CFR 1910.120).

Original (intended) use of IDLH value

• Key component of the NIOSH Respirator Selection Logic [NIOSH 2004],

– Ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment; and

– Is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted.

9

IDLH Values

• IDLH values reflect airborne concentrations; applied to inhalation exposure– Assume that other routes are of limited importance

• Dermal• Ingestion

• Based on health effects (toxic) considerations– Exceptions:

Safety Considerations [10% lower explosive limits (LEL)]

• Based on a 30-minute duration– Theorized escape period in the event of respirator failure

Available via NIOSH website

Revised (1994) IDLH Values and Support Documentation

• No standardized rationale

• Limited transparency

• Limited discussion on the critical effects, data or process

• Do they reflect current state of knowledge?

Example: Acetaldehyde


Objectives of Current IDLH Project

• To update the scientific basis and risk assessment methodology used to derive IDLH values

• To provide a consistent and transparent rationale and derivation process for IDLH values

• To demonstrate how scientifically credible IDLH values can be derived based on available data resources

Draft IDLH CIB

• Current Intelligence Bulletin (CIB)

• Presents the scientific rationale and derivation process for IDLH values

– Weight of evidence approach

– Not a formulaic approach

• No magic formula for setting an IDLH value

Draft IDLH CIB

• Incorporates the process used to establish AEGLsand other acute exposure guidelines– Approved by the NAS and NRC

– Current state of knowledge

• Provides guidelines for:– Selecting critical endpoint data [point of departure

(POD)]

– Time scaling

– Selection of uncertainty factors (UF)

• “Defines” IDLH values and their purposes

– Develop health protective IDLH values

– Safety issues are communicated, but are not the basis of the IDLH value

• Defines the use of IDLH values

Draft IDLH CIB

Defines the Purpose of IDLH values

• Purpose of an IDLH value– Definition from the NIOSH

Respirator Decision Logic

1. to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and

2. is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted

• Traditional vs. non-traditional uses– Respirators

– Emergency and workplace planning

• Improper uses – Not an OEL

– Should not be used as a relative index of toxicity*

Additional information

• 30-minute value

• Health (toxicity) based vs. Safety based

– Respirator uses

• Sensitive populations

Select Candidate Chemical Substance

Conduct and Review Literature Search

Array Key Data

Yes

NoAcute Inhalation data?

HumanNOAEL/LOAEL/BMDLC50

RD50

Time Scaling

Uncertainty Factor Applied

Final IDLH Value

WOE Analysis Determines

Potential IDLH Value

Repeat InhalationSAROther Routes

Time Scaling

Uncertainty

Final IDLH Value

WOE Analysis Determines

Potential IDLH Value

Other Data?

Insufficient

No

Yes

Derivation Process

• Hazard characterization

– Review of human & animal data

– Identification of critical effects

– Mode of Action (MOA)

• General description of how a chemical exerts its toxic effects

– Direct irritant vs. Metabolic pathway vs. Neurotoxicity

• Used to determine UF, time extrapolation, choice of POD and consideration of interspecies differences

– Identification of a POD

• NOAEL, LC value data, LOAEL, NOEL, LOEL, BMC, etc.

• Time scaling – Duration adjustments to determine 30-minute

equivalent exposure concentrations– ten Berge equations (Cn X T)– Default values vs. Chemical specific models

• Additional dosimetric adjustments– Hydrolysis Products

• e.g., sulfur trioxide

– Analogous compounds• e.g., HI, HBr

– Route to route extrapolation

Derivation Process

• Application of appropriate Uncertainty Factor (UF) – Based on the study and POD– Provide guidelines to selecting UF based on NIOSH

analysis and other lines of data – Not a magic formula– Preferred ranges for different PODs; guidance

provided

• Determination of the final risk value

Derivation Process

Simplified IDLH equation

Risk Value =Time-adjusted POD

UF[POD = Point of Departure

UF = Uncertainty [

Case study

Vinyl Acetate

Data (health endpoints) that may serve as the basis of an IDLH values

Impairment of ability to escape

Irreversible health effect

Lethality

Cri

tica

l He

alth

En

dp

oin

t

IDLH Value

28

Potential Health Endpoints that May Qualify as IDLH

• Impairment of ability toescape

• Serious irreversibleeffects

• Death

Respiratory– Irritation– Pulmonary edema – Dyspnea/Respiratory depression

Neurological– CNS depression– Cholinesterase (AChE) inhibition – Behavioral changes/disorientation– Muscle fasciculation/twitching – Severe intoxication– Ataxia/Incoordination

Other – Cardiac – Development/Reproductive– Ocular damage– Sensory irritation/ Vision-impairing

lacrimation

Example: Vinyl Acetate

• Human data– No lethality data– Limited non-lethality data

• Irritation at 4 to 72 ppm– At 72 ppm, eye irritation and slight URT irritation (30 min)– At 22 ppm, eye irritation described as intolerable (10 min)

» Quality of study ?

• Animal data– Lethality data available in multiple species

• Mice for sensitive to vinyl acetate than other animals

– Non-lethality data limited• LOAEL of 1000 ppm for histopathologically observed degeneration,

necrosis, and exfoliation of olfactory epithelial cells of rats exposed to vinyl acetate for 6 hours


Species Reference

LC50

(ppm)

Time

(minutes)

Adjusted

30 minute

(0.5-hour)

LC* UF†

30 minute

(0.5-hour)

Derived Value

(ppm)§

Mouse Smyth and Carpenter [1973] 1460 240 2920 30 97.33

Rabbit Smyth and Carpenter [1973] 2760 240 5520 30 184.00

Rat Smyth and Carpenter [1973] 3680 240 7360 30 245.33

Guinea Pig Smyth and Carpenter [1973] 5210 240 10420 30 347.33

Table A.3: Calculation of 30 minute (0.5-hour) Derived Values for Vinyl AcetateLC50: The statistically determined median concentration of a substance in the air that is estimated to cause death in 50% (one

half) of the test animals; ppm = part per million; UF = uncertainty factor

*For exposures other than 30 minutes the ten Berge et al. [1986] relationship is used for duration adjustment (Cn x t = k); no empirically

estimated n values were available, therefore the default values were used, n = 3 for exposures greater than 30 minutes and n = 1 for

exposures less than 30 minutes.

• UF selection: 30 – Effects severity (type –lethal ) (3X); [LC50/3 = LC01] – animal to human differences (3X)– human variability (3X)

• Risk values: ~100 to 350 ppm

• Human data comparison– Supportive, but not sufficient to be basis of IDLH value – Quality issues

• Final IDLH value: 100 ppm (97 rounded to 100)

• NIOSH REL = 4 ppm [(C) 15-min]


New support documents

• Will provide:– Critical assessment of all reviewed data

• Human vs. animal

• Lethal vs. non-lethal

– Discussion on the critical toxicological effects• MOA (irritant vs. CNS)

• Lethal vs. irreversible vs. impairment

– Application of time scaling, dosimetry adjustments, UF, etc.

– Additional information

Next Step

• External peer review– Currently being concluded (February – May 2011)

• Specific topics addressed– Safety vs. Health-based IDLH values?

– Non-inhalation IDLH values? • Dermal

– Definition and Purpose of IDLH values?

– Additional information?

Next Step

• Revision and publication of CIB (2011-2012)

• Development of IDLH values for 150+ high priority chemicals

– Updated IDLH values

– New IDLH values

Summary

• Transparent and consistent process

– Weight of evidence approach

– Not a cook book approach

– Need to critically evaluate each chemical on a case by case basis

Questions?

G. Scott Dotson, PhD, CIH

Industrial Hygienist

CDC/NIOSH/EID513.533.8540

[email protected]

Derivation of IDLH Values - Esafetyline - the source for … s/EEI Spring... · 2011-10-25 ·...

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