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Solvents by the Numbers

by Charlie Simpson

Rating systems seem to be everywhere, from the Richter scale to movies and music ratings. In fact, anything that has the potential to pose a "danger" can be rated to help rank the threat. But just like the definition of danger can be relative so can be the rating itself. Today's cleaning industry is no different; well at least it's becoming a lot less different. As corporations strive to effectively use and safely dispose of solvent-based cleaning chemistries, firms are looking at all systems, methods or tools that can provide them with further insight into the ramifications of the chemistries they may choose. The Indiana Relative Chemical Hazard Score (IRCHS), generated by the Clean Manufacturing Technology and Safe Materials Institute (CMTI, Purdue University, Indiana) provides one such tool, that users of chemistry can turn to when evaluating their options.

The Indiana General Assembly created the CMTI in 1990. In 1993 the Indiana Pollution Prevention Board selected Purdue University to establish and operate the Institute and it formally began operations on January 1, 1994. The Institute provides technical assistance and education services to a variety of industries. The purpose of the Institute is to act as a focal point for coordinating and deploying technical assistance, outreach, education, planning services and research to facilitate the adoption of pollution prevention/clean manufacturing strategies by manufacturing facilities.

Originally funded by the EPA, IRCHS' major goal to develop a "reliable measurement method" to rank the toxic impact of chemicals was achieved by expanding upon the University of Tennessee's (UTN) chemical ranking system, also developed for the EPA.

CMTI has recently added foundries to this list of the "four priority manufacturing sectors" of metal finishing, plastics, wood finishing, and automotive parts, originally the focus of the program. In addition, the IRCHS (formerly know as Pollution Prevention Progress Measurement Method or 3P2M) system has been used by universities and government agencies throughout the country.

According to IRCHS, the UTN method evaluates each chemical separately and assigns a hazard value based upon the chemical's hazard towards the environment, with emphasis upon the aquatic ecosystem. The IRCHS algorithm includes hazards towards air quality, potential for soil and groundwater contamination, and stratospheric ozone depletion. This expanded algorithm assigns chemicals an environmental hazard value. The IRCHS team also developed an algorithm to assign chemicals a hazard value based upon its hazard towards the factory worker. The two hazard values are combined and the average of the two becomes the combined hazard value for the chemical.

Shayla Barrett, Process Engineer, and the IRCHS project manager, explains that the first EPA Pollution Prevention Incentive for States (PPIS) grant for 3P2M was awarded in 1994, because the EPA was looking for methods to measure progress in pollution prevention, and gave top priority towards the PPIS grant applications that focused on this endeavor. "The Indiana Relative Chemical Hazard Scale is ongoing. We are always adding new chemicals to the list of chemicals assigned a score. And although the Indiana Clean Manufacturing Technology and Safe Materials Institute (CMTI) will not be adding to the algorithm. However, other organizations or universities may add to the criteria," says Barrett.

The Formula
The combined hazard value allows comparative ranking of hazard among chemicals, but does not measure pollution prevention progress. The IRCHS algorithm measures this multiplying the amount of the chemical used by its hazard value and normalizing the product by units of production. This will allow comparisons among scales of production and across time, providing a method adaptable to all stages of the product life cycle and all sizes of facilities and sectors. The IRCHS group investigated defining materials usage and units of production and concluded that these terms would be best defined according to individual manufacturers standards.

To date, hazard values have been assigned to over one thousand chemicals. The hazard values are on CMTI's Website, www.ecn.purdue.edu/CMTI, which averages 500 hits per month. These chemicals are all of the CERCLA chemicals plus any additional chemicals commonly used by the four priority manufacturing sectors. The most recent additions to the list were added the first half of 2001, and were all of the Extremely Hazardous Substances (EHS) identified by OSHA and EPA, all of the Stratospheric Ozone Depleters (SOD) identified by EPA, and the thirty seven High Production Volume (HPV) chemicals designated by EPA for mandatory testing.

Barrett states that the program allows chemical vendors to "advertise their products as less toxic than similar products, if 3P2M verifies this," and is being received "very well by the vendor community, who are aware of it." And for the solvent end user, the program lets them compare the toxicity of similar products, which can be a huge aid in determining which product to use if all else is equal or near equal.

The final measurement method for use by the Institute is:

Total Hazard Value = normalized worker exposure hazard value + normalized environmental hazard value /2 or

[(1.15)(HVhlth X HVexp+2HVsafe)]+[(HVwater+HVair+HVland+HVglobal)/3.5]/2 or


Environmental Hazard Value
The environmental hazard component consists of four parts: the Water, Air, Land and the Global Hazard Values. The water hazard value will be the University of Tennessees already determined hazard value, while the air hazard value will be the sum of the hazard values assigned if the chemical is:

  • A criteria pollutant (HV=20)
  • A Hazardous Air Pollutant (HAP) (HV=40)
  • A High Risk Pollutant (HRP) (HV=20)
  • An Extremely Hazardous Substance (EHS) (HV=20)

The land hazard value will be the hazard value assigned if the chemical is:

  • On the Hazardous Waste P List (HV=70)
  • On any of the Hazardous Waste F, K, or U Lists (HV=35) (F001 - F005 only; Chemical must be specifically listed on K list)
  • Exhibits the Hazardous Waste Characteristic of: Ignitability (HV=15), Reactivity (HV=15), Corrosivity (HV=15), and Toxicity (HV=15).

The global hazard value will be the hazard value assigned if the chemical is a Stratospheric Ozone Depleter (SOD). These values are:

  • 50 if the chemical is a Class I SOD
  • 25 if the chemical is a Class II SOD

Therefore, accordingly, the components of the environmental hazard value are:

  • HVwater = Normalized UTN HV
  • HVair = HVcrit.+HVhrp+HVvhap+HVehs
  • HVglobal = HVsod
  • HVland = HVvp+HVu+HVign+HVreact+HVcor+HVtox

The values for the water, air, and land hazard portions of the algorithm will be normalized to a highest probable score of 100. The value for the global hazard portion will be normalized to a highest probable score of 50. These four parts will be added together and divided by 3.5 (the global hazard value is 1/2 the value of the other three) to determine the environmental hazard value. The final Environmental Hazard algorithm is HVenvhaz = (HVwater+HVair+HVglobal+HVland)/3.5.

Worker Exposure Hazard Value
The worker exposure component will consist of three parts: the Health Effects, the Routes of Exposure, and the Safety Hazard Value. The health effects hazard value will be the sum of the Chronic Hazard Value and the Acute Hazard Value. The chronic hazard value is the more stringent of the toxic or the carcinogenic hazard values. The toxic hazard value (HVtox) is based upon the chemicals Threshold Limit Value (TLV). The hazard values assigned are:

(TLV) (mg/m3) HVtox
>2500 0.0
2500 but >250 1.0
250 but >25 2.0
25 but >2.5 3.0
2.5 but >0.25 4.0
0.25 5.0

The carcinogenic hazard value (HVcar) is based upon classifications from EPA ratings and the American Conference of Governmental Industrial Hygienists (ACGIH) ratings. The hazard values assigned are:

EPA Rating ACGIH Rating HVcar
E A5 0.0
D A4 0.0
C N/A 1.5
B2 A3 3.5
B1 A2 4.0
A A1 5.0

The acute hazard value is the hazard value assigned based upon the Short Term Exposure Limit (STEL) of the chemical. If a STEL exists, the STEL hazard value (HVstel) is 0.5. If a STEL does not exist, the HVstel is 0.0. The routes of exposure hazard value will be the sum of:

  • The Vapor Pressure Hazard Value (HVvp)
  • The Oral Hazard Value (HVoral)
  • The Skin Hazard Value (HVskin)
  • The Dust / Mist Hazard Value (HVdm)

The HVvp is based upon the vapor pressure of the chemical at 25° C. The hazard values assigned are:

Vapor Pressure (torr) HVvp
<0.076 0.0
0.076 but <0.76 1.0
0.76 but <7.6 2.0
7.6 but <76 3.0
76 but <760 4.0
760 5.0

The HVoral is based upon whether or not the chemical can be absorbed through the mouth. Currently, only lead is scored as an oral hazard. If lead is in the chemical compound, the HVoral is 1.0. If lead is not in the chemical compound, the HVoral is 0.0.

The HVskin is based upon whether or not the chemical can be absorbed through the skin. If it can be absorbed as defined by ACGIH, the HVskin is 0.5. If it cannot, the HVskin is 0.0.

The HVdm is based upon the ability of the chemical to produce dusts or mists. Here are the values assigned:


Condition: Melting Point (MP) > 25ēC, presumed solid at Standard Temperature & Pressure (STP), no note on TLV entry for dust
HVdm: 1.5

Condition: TLV entry notes a value for "dust"
HVdm: 3.5

Condition: If a chemical may be handled or used both as a solid dust and a sprayed solution of that solid (and neither "dust" or "mist" is present at its TLV entry), or is used in plating solutions and is capable of creating mist when heated or agitated, then it is given a combined score of:

Condition: If the chemical's MP is close to 25ēC; can exist either as liquid or solid at room temperature
HVdm: 2.0

Condition: If a solid is entered in UTN list of compounds (using specific surrogates) only as a solution of soluble solid or characteristically used only as liquid solution
HVdm: 1.5

Condition: If a solid tends to be present in airborne smoke particulates resulting from combustion, especially polycyclic aromatic hydrocarbons and chlorinated dibenzo-dioxins and furans
HVdm: 1.5

Condition: Friable asbestos, all types
HVdm: 5.0


Condition: MP < 25ēC, BP > 25ēC, presumably liquid at STP, especially liquid inorganic acids and short-chain fatty acids, especially acetic acid, or alkalis or alkali solutions, presumed capable of creating mist, either when mechanically agitated or splashed or when heated, but no mention in TLV entry of "mist". Includes the gases hydrogen chloride, hydrogen bromide, hydrogen fluoride, hydrogen iodide, ammonia and hydrogen cyanide, which, when dissolved in water, are known respectively as hydrochloric acid, hydrobromic acid, hydrofluoric acid, hydroiodic acid, ammonium hydroxide, and hydrocyanic acid
HVdm: 1.5

Condition: TLV entry notes a value for "mist"
HVdm: 3.5

Condition: MP > 25ēC, presumed solid at STP. No note on TLV entry for dust, but may be handled, sprayed or used as solution, in characteristic use - usually a pesticide, herbicide or surface spray operation.
HVdm: 1.5


Condition: Boiling point < 25ēC, presumed gas


The safety hazard value will be the sum of the flammability hazard value (HVflam), the reactivity hazard value (HVreact) and the corrosivity hazard value (HVcor). The HVflam and HVreact are based upon the flammability of a chemical as defined by the National Fire Protection Association (NFPA). The value is the same as that given by NFPA.

NFPA HVflam and HVreact
0 0.0
1 1.0
2 2.0
3 3.0
4 4.0

The HVcor is based upon the corrosivity of the chemical as defined by the U.S. Department of Transportation (DOT). The hazard values are:

DOT Classification HVcor
None 0.0
III 2.0
II 3.0
I 4.0

Therefore, the components of the worker exposure hazard value are:

  • HVhealth effects = HVchronic+HVacute
  • HVroutes of exposure = HVvp+HVoral+HVskin+HVdm
  • HVsafety = HVflam+HVreact+HVcor

The safety hazard value is multiplied by 2 as a weighting factor and the final Worker Exposure algorithm is: HVwrk exp = (HVhealth)(HVexposure)+2(HVsafety).

What the Experts Say
Jack Scambos, product manager at Aqueous Recovery Resources (Bedford Hills, NY) believes that the IRCHS program "addresses the need to build upon true data," presenting it in a concise, useable format. "People die for this type of unbiased data," states Scambos. By combining numerous other algorithms and formulas, he maintains that more people will be apt to use this "Cliff Notes view" of a solvent. Although Scambos is optimistic about program being a great start, he advises that "only time will tell" if any data is "true data."

Richard Morford of EnviroTech (Melrose Park, Ill.) sees the program as providing an "apples to apples comparison." Morford explains that although this approach may be in an early development stage this type of relative comparison has been missing in the industry, and will soon be demanded of the industry. But Morford, whose Ensolv family of solvents has been rated 8.2 by the formula, also sees the scale as just another tool, albeit "more thorough," in a series of tools that users can leverage to help with chemistry decisions. To put the ranking in a bit of perspective, Methyl Chloroform (1,1,1 Trichloroethane) ranked 28.35, sulfuric acid ranks 31.4 and methanol ranks 24.7. But, like Scambos, Morford cautions that any system that tries to compare toxicity levels should not be used the sole source of information. "Nothing in chemistry is written in stone," says Moreford. "Because an solvent ranks 24 versus one that ranks 8, doesn't make one product three times better than the other."

Being as the EPA no longer funds the project, it was difficult to find someone who could comment in detail on the project. However, Phil Kaplan, Pollution Prevention Coordinator U.S. EPA Region 5 (Chicago, which originally funded the project in 1994), believes this remains important work and it's a good concept to try to gauge toxicity in order to "gain more bang for your buck on pollution prevention."

John Stemniski, however, a retired consultant (Swanpscott, Mass.) who has spent decades working with various chemistries in the military and private sectors, and has seen his share of systems, doesn't put much stock in formulas. "Math is an exact science, chemistry is not," he poignantly observes. "When you put something in a table, and it is a 3 on a scale of 1 to 5, you must remember it is a 3 only on that particular scale." So where Stemniski says it may pass the "30 day test," he questions what happens three years or even 30 years down the road.

IRCHS' Barrett acknowledges that, "When there is a mixture of chemicals, the algorithm does not take into account any benefits or detriments gained by the mixture. It simply multiplies the hazard value of each component by the percentage of that component, and then adds the scores for the final hazard value of the mixture." He indicates that some organizations object to the carcinogenic scores, but emphasizes that all components are gleaned from existing data. EnviroTech's Moreford sites the zeroing out of unavailable data in certain parts of the formula as a drawback to the algorithm; but believes that as more information becomes available, the better the process will become.

Tom Hand of Honeywell FM&T (Kansas City, MO) believes that the system offers useful information. However he points out that, "when we need to do anything here with solvents or chemicals, I never use any of these sorts of algorithms, because our own ES&H team will base all their thoughts on the same things the [IRCHS] teams did to make their site useful. But our people will trust themselves and no others." He wonders if this is also how other major organizations and companies will view it as well. "People in the cleaning business will understand how and why the algorithms work and are useful and why the chemicals are where they are but novices may not." Because of that, Hand questions if they will use such an algorithm all that much.

Still the IRCHS system has been reviewed and used by several universities and government agencies throughout the nation. MIT used the system to evaluate Massachusetts' Toxic Release Inventory (TRI) chemicals to determine whether or not the states manufacturers were releasing less toxic substances. Brooks Air Force Base is using the system to evaluate proposed chemical usage. The Minnesota Office of Environmental Assistance has adopted the system to evaluate products containing listed metals. The Environmental Defense Fund lists the IRCHS as one of five "hazard ranking" systems that it using to develop hazard scores for its Environmental Score Card.

Whether the algorithm is used often or randomly all involved agree that it is to be treated as just one component in your calculations and determination, and no source should ever be used as the "be all and end all" of your decision to use a particular solvent.


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