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1 February 200 8 Revised TPQ Method for EHS solids in solution

I. Introduction:

EPA is proposing a rule to consider an alternative approach for the threshold planning quantity (TPQ) for chemicals on the Extremely Hazardous Substances (EHSs) list that exist as solids in solution form. The current TPQ for solids in solution is based on an assumption that the entire quantity of the solid chemical in solution at a facility has the potential to become airborne in the

event of an accidental release

. Syngenta petitio ned EPA to revise the TPQ for the chemical paraquat dichloride, a solid chemical which is used commercially in solution. EPA researched data and studies on aerosol air releases of liquids and solutions to investigate how much aerosol

remains airborne duri ng accidental air releases. Results of this search (USEPA May 2007) show

that much less than 100% of a n amount of solid in solution involved in an accidental release to air would remain airborne for distances beyond a facility ’ s fence line. Therefore, EP A believes that the assumption of 100% potential airborne release for solids in solution is too conservative and a new approach is warranted.

II. B ackground

The TPQs were originally developed as relative measures of concern rather than absolute values.

The threshold planning quantity is not necessarily applicable to any specific situation with respect to predicting the actual quantity or “safe” level. This is best determined by the local planning authorities using specific parameters for that facility becau se there are wide variation of

site

- specific conditions that affect airborne dispersion.

TPQs were developed using a ranking approach based on each chemical’s physical state, acute toxicity and “V”, the potential for the chemical to become airborne. The ranking index was defined as the Level of Concern (LOC) divided by V. V was set equal to 1 for gases and solids in powder form with particle size less than 100 microns. For solids with particle size of 100 microns and higher, the TPQ is 10,000 pounds. For chemicals that are molten solids, the amount

on

- site is multiplied by 0.3 to before comparing to the lower TPQ for reporting purposes because 0.3 is the maximum fraction estimated to potentially volatilize.

For liquid EHS, V is a calculated number bas ed on a volatilization modeling equation and is actually the rate of volatilization (mass vaporized per unit time) per mass of liquid spilled for a spill, assumed to be 1 cm deep.

III. P roposed Revised Method for Solids in Solution TPQ

Based on review of expe rimental data on accidental releases of solutions, EPA is proposing that the maximum fraction of a release of solid in solution aerosols that could be expected to remain airborne and affect a community outside a facility’s fenceline is 0.2. Facilities cou ld use theDRAFT SUBMITTED FOR PEER REVIEW

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2 maximum expected airborne release fraction multiplied by the amount of chemical on site and then determine if this amount exceeds the established lower TPQ. This procedure is the same as is done now for molten solids, except that molten solids apply a fraction of 0.3 (30%).

IV. Experimental data on accidental releases of aerosols

EPA found a comprehensive study by US Department of Energy ( DOE ) that compiled experimental data on accidental releases of heavy metal (uranium) salts in solution (USD OE 1994) . The study estimated the fractions of liquid aerosol releases that remained airborne for

various release scenarios. EPA reviewed and summarized the scenarios with the highest airborne fractions (ARF) in USPEPA, May 2007. The accidental release s cenario with the highest

airborne release fraction had an ARF of 0.2 The airborne fractions generally contain aerosol sizes less than or equal to 100 microns, the size above which droplets are expected to fall out before they reach a community outside a facility.

EPA also looked at experimental data collected by the Center for Chemical Process Safety (CCPS) for aerosol releases of water and cyclohexane, although these liquids did not contain any solid material in solution. The reported airborne rele ase fraction for water was 0.03 to 0.54 and for cyclohexane was 0.36 to 0.94. CCPS also had experimental release data for CFC

- 11 and chlorine (both gases) and methylamine (a highly volatile chemical), but we did not consider this data for use as a good an alogy because the releases were probably more in the form of vapor than liquid aerosols.

V. Use experimental aerosol release data to revise TPQs for EHS solid in solutions.

A. Appropriate experimental data

The original TPQ rationale for solid in solution T PQ was based on using conservative worst case scenarios and assuming 100% of the solution would be released as aerosol. Both the DOE and CCPS data support the argument that assuming that 100% of the liquid aerosol release remain s airborne is too conservat ive.

Cyclohexane is a more volatile chemical than water (95 vs 24 mm Hg vapor pressure), so its higher airborne release fraction would not be comparable for a solid chemical in water solution. Also, the experimental data for water and cyclohexane used b y CCPS had much larger mean aerosol diameter sizes, generally over 100 microns . Because a erosols larger than 100 microns

will likely fall out of the air before they reach a community, the CCPS water and cyclohexane aerosol experimental data would not be u seful for our purposes of determining TPQs.

The DOE data have results from several release scenarios with the maximum airborne release

fraction of 0. 2

. The value is based on the scenarios of aqueous solution or air dried salts under gasoline fire on a m etal surface. Using the highest airborne release fraction rather than anDRAFT SUBMITTED FOR PEER REVIEW

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3 average result of the scenarios would be more consistent with the intent of the emergency planning program to plan for worst case scenario. Th is data is a good surrogate to use to p redict maximum potential aerosol release fraction of EHS solids in solution in event of an accidental release. Water is probably the most common solvent that would be used with most of the EHS solids, whether they are dissolved, suspended or emulsified in water. Many of the EHS solids are pesticides and pesticides are commonly applied as water solutions or emulsions.

B. Consis tency issues

Liquid EHS could also be released accidentally as aerosols via the same catastrophic scenarios (overpressure, superhea ting). It could be argued that perhaps the TPQ method for solids in solution could apply to liquids. However, this goes against the intuitive ranking of the extent and likelihood of airborne release by physical state as being higher for gases, lesser for liquids and even less for solids in solution. Currently the release scenario used for developing the liquid TPQs requires only a spill of the liquid, a loss of containment. The liquid then escapes into the air by volatilization. An airborne release of solids in solution will require more than a failure of containment and will need an energy source such as overpressure or high temperature to drive the solution into the air and create aerosol droplets. Not all of the droplets will stay airborne (unlike v olatilized vapors) and affect the community, whose exposure depends on droplet size and distance to the facility fence line.

Thus, to address any consistency issues, EPA also want s to determine if the current TPQ method for liquids g ives more conservati ve (or at least as conservative) TPQs (lower threshold s ) than if

the same proposed TPQ method for solids in solution was applied to pure liquids. A new liquid TPQ based on V=1 was calculated. Then this TPQ was multiplied by 5 (1 / 0. 2 ) to determine the

a mount of liquid a facility could have on

- site and this result is referred to as the effective TPQ. For 117 out of the 163 EHS liquids, current TPQs based on volatilization were still smaller than or equal to the new effective TPQs based on aerosolization. Most of the other 46 liquids had effective TPQ s th at were half the current TPQ

.

VI. Alternative approaches considered

A. Use original ranking index method and develop a new TPQs

TPQs were developed using a ranking approach based on each chemical ’ s physica l state, acute toxicity and “ V ” , the potential for the chemical to become airborne. The ranking index was defined as the Level of Concern (LOC) divided by V. V was set equal to 1 for gases and solids in powder form with particle size less than 100 microns

. For solids with particle size of 100

microns and higher, the TPQ is 10,000 pounds. For chemicals that are molten solids, the amount

on

- site is multiplied by 0.3 to before comparing to the lower TPQ for reporting purposes because

0.3 is the maximum frac tion estimated to potentially volatilize.DRAFT SUBMITTED FOR PEER REVIEW

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4 For liquid EHS, V (the potential to become airborne) depends upon the property of volatility (evaporation of liquid into gas phase) . The same calculation for V for liquids cannot be used for

solids which are basi cally non

- volatile materials at ambient temperatures

.

One might argue that for solids in solution, V could equal the airborne aerosol fraction released based on experimental data. However, this V would not be directly comparable to the V

calculated for liquids, because it would have no time component.

B. Use old TPQ multiplied by maximum aerosol airborne fraction.

Developing and listing a third set of TPQs for solids in solution could be potentially confusing to the regulated community. For each solid chemical, there already exists two TPQs, one developed based on the ranking index methodology of (Index = Level of Concern/V ) and on the default TPQ of 10,000 pounds for all solids not meeting criteria for using the lower TPQ.

VII. Aerosol size

One issue that EPA agreed to consider in this rulemaking was whether aerosol size should be used as a factor in developing new TPQs for solids in solution

. Particle size was considered as a factor for the TPQ for powdered solids. In the EHS final rule of April 22, 1987, EPA modified the TPQs for solid chemicals so that only powdered solids with particle size less than 100 microns would be subject to the lower TPQ. Otherwise the TPQ defaults to 10,000 pounds.

This decision was based on data indicating that a parti cle of a size less than 100 microns are not likely to be deposited more than 100 meters from the source. For example, for a typical wind speed of 10 mph, particles larger than about 100 microns are like to settle out within 6 to 9 meters from the point of emission. Particles that are 30 to 100 micron in diameter are like to undergo impeded settling and are likely to settle with a few hundred feet (USEPA 1995). The 100 micron cutoff is also consistent with CERCLA regulations (for reportable quantities) wh ich also uses a 100 micron particle size level for powdered materials. For purposes of establishing threshold planning quantities, EPA chose a distance of 100 meters (330 feet) to represent the distance from a source inside a chemical facility to the poin t where the community might be exposed.

A. Syngenta ’ s proposal

The DOE aerosol release data was developed to estimate airborne fractions of liquid aerosol

releases that were below respirable size. By DOE ’ s definition, respirable size particles are th ose that can be transported through the air and inhaled into the human respiratory system and are commonly assumed to include particles 10 micron Aerodynamic Equivalent Diameter (AED) orDRAFT SUBMITTED FOR PEER REVIEW

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5 less. A consultant for Syngenta recalculated some of the DOE airbor ne aerosol fractions using the raw experimental data to include only aerosols sizes ≤ 4 micron diameter for some accident

scenarios. This resulted in smaller airborne fractions. Syngenta claim s this approach was appropriate because the inhalation acute toxicity test for paraquat dichloride is based on 4 micron size particles.

1

. Small size aerosols used in toxicity tests

Aerosols may be defined as a suspension of solid or liquid particles in air. Inhalation acute toxicity tests are purposely designed with very small diameter particles in order to ensure that particles are small enoug h to enter rodent lungs and test the toxicity in the lungs. Larger particles may not enter deep areas of the lungs and thus test results may be misinterpreted if little inhalation toxicity is shown. EPA is not attempting to use the airborne aerosol frac tion for purposes of risk assessment, but only as a tool to set screening levels for the amount of chemicals

on

- site which may potentially cause harm if accidentally released. One cannot assume that the

size aerosols used in a n animal laboratory test would be the same as those in aerosols people may be exposed during an accidental release of a solution of solid chemical.

2

. Particle size and exposure

According to EPA, inhalable particles enter the respiratory tract, including the head airways and

are gene rally ≤ 100 microns . Thoracic particles ( ≤ 10 microns) travel past the larynx and reach the lung airways and the gas

- exchange regions of the lung. Respirable particles ( ≤ 4 microns ) are a subset of thoracic particles that are more like to reach the gas

- e xchange region of the lung. DOE uses a different size cut (< 10 micron) because radioactive materials they are concerned with can be removed from the skin but not following inhalation or ingestion.

Most particles that are deposited in upper airways are trapped in mucous that moves to the throat

and is swallowed in a few hours. Thus instead of inhalation exposure deep in the lungs, exposure to larger particles of chemicals may occur through dermal exposure to mucous membranes or oral exposure through swa llowing. Emergency planning for EHS chemicals is not limited to inhalation exposure only although many of the EHS chemicals listings are based on inhalation toxicity. Although a irborne exposure is the mostly likely route of exposure , it is not the only r oute of exposure . EPA is concerned about all routes of exposure (inhalation, dermal and oral) to the community. Thus exposure to larger size aerosols (e.g. those above 4 or 10 microns) by any route should not be ignored when setting TPQs.

3. Solvent evap oration from aerosols

E ven after liquid aerosol droplets are released, some of the solvent may evaporate in air. This

would result in even smaller size of aerosols or solid EHS particulates in the air to which a community would be exposed. One concern i s that droplet of size greater than 100 micron couldDRAFT SUBMITTED FOR PEER REVIEW

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6 settle quickly, dry into a smaller particle size and then become airborne again (resuspension).

I n event of an accidental release, the responsible party should cleanup chemicals deposited on facility grounds before additional exposure to the community would take place.

Data from the DOE Handbook for resuspension of liquids and powders from soils and other surfaces can be used to estimate the fraction of material resuspended to be from 4E

- 3 to 1E

- 2.

If the worst case airborne fraction that leaves the facility’s site is assumed to be 2E

- 1, the n the

fraction of the release that would fall out and be deposited on the facility’s site would be 8E

- 1. Assuming that a worst case fraction 1E

- 2 ( whether as dr ied solids or liquid droplets) o f this deposit could be resuspended, the additional fraction of the original release to be come airborne

would be 8E

- 3 (8E

- 1 times 1E

- 2). Adding the resuspended fraction of 8E

- 3 to the original

airborne release fraction of 2E

- 1 would yield a total fraction of 0.208. This does not much add much to the original amount and rounding appropriately to 1 significant digit would still result in

an overall ARF of 2E

- 1.

B. Feasibility of applying aerosol size cutoff

The particle s ize of the accidental aerosol release is the relevant consideration and not the

solution form stored on

- site. Aerosol size of an accidental aerosol release is not likely to be known or measured by facilities. EPA was able to apply a particle size cutoff for powdered

solids because the form of the chemical released is the same as that stored on

- site

. Therefore, a particle size cutoff that facilities could apply to solids in solution similar to the size cutoff for powdered solids would not be feasible.

C

. Size of experimental aerosols

Most of the DOE experimental aerosol release data had aerosol sizes of less than 100 microns. The water and cyclohexane aerosol release data compiled by CCPS had much larger mean aerosol diameter sizes, generally over 1 00 microns. Because it is likely that aerosol releases with diameters larger than100 microns will fall out of the air before they reach a community, the water and cylcohexane aerosol experimental data are not that useful for our purposes of determining TP Qs for solids in solution.

REFERENCES

USDOE. 1994. DOE Handbook, Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities. December 1994. US Department of Energy, Washington, DC

20585 DOE

- HDBK

- 3010

- 94. Volume 1

- A nalysis of Experimental Data and Volume II

Appendices.

USEPA. May 2007. Literature Survey for Liquid Aerosol Release Data to Support TPQDRAFT SUBMITTED FOR PEER REVIEW

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7 Methodology for EHS Solids in Solution , May 11, 2007. Office of Solid Waste and Emergency Response, Office of Emergency Management.

USEPA 1995. AP

- 42 Emission Factors, Fifth Edition, Volume I. Chapter 13 Miscellaneous Dust Source. 13.2 Introduction to Fugitive Dust Sources. USEPA, Off ice of Air Quality Planning and Standards.