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OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 1338-23-4 Chemical Formula: C8H18O6

OSHA did not formerly have a limit for methyl ethyl ketone peroxide (MEKP). The Agency proposed a PEL of 0.2 ppm (1.5 mg/m 3) as a ceiling for this substance to protect workers against the significant risk of eye and skin irritation, as well as kidney and liver damage; this limit is consistent with that of the ACGIH. NIOSH (Ex. 8-47, Table N1) concurred with this limit. In the final rule, OSHA has determined that the data available at the present time indicate that 0.7 ppm (approximately 5 mg/m3) is an appropriate level at which to establish a PEL, and the final rule establishes this limit. MEKP is sold commercially as a colorless liquid mixture consisting of approximately 60 percent MEKP and 40 percent diluent; the diluent is added to reduce MEKP's sensitivity to shock.

The health effects data for MEKP in animals rely primarily on a study conducted in 1958 by Floyd and Stokinger (Ex. 1-783). In a series of experiments conducted in rats, mice, and rabbits to determine the toxicity of MEKP by various routes of exposure, these investigators found that inhalation exposure for four hours to a concentration of 200 ppm was fatal to 50 percent of rats, and a four-hour exposure to 170 ppm was fatal to 50 percent of mice. Inhalation of MEKP vapors produced petechial and gross hemorrhages of the lungs in rats after four-hour exposures; liver and kidney damage was also observed (Floyd and Stokinger 1958/Ex. 1-783). Two drops of a 40-percent solution of MEKP in dimethyl phthalate caused severe damage when instilled in rabbits' eyes, but at 3 percent, a moderate, transient reaction was produced. The direct application of MEKP to closely shaved rabbit skin caused no immediate discomfort but did cause a severe delayed reaction, consisting of erythema, edema, and vesiculation within two or three days; of the four organic peroxides tested (di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and methyl ethyl ketone peroxide), MEKP exhibited the greatest toxicity. The maximal nonirritating strength of MEKP applied dermally was 0.6 percent. In addition, rats died or showed marked evidence of cumulative systemic effects after either oral or intraperitoneal administration of MEKP at 20 percent of the LD(50) level for three days/week for seven weeks (Floyd and Stokinger 1958/Ex. 1-783).

OSHA received several comments on the proposed PEL for MEKP (Exs. 8-47, 8-86, 3-902, 144, 155, 181, and 3-1172; Tr. 11-265/266). Robert Schumacher, a certified industrial hygienist representing a group of six manufacturing companies (including the U.S. Marine Corporation), stated that the proposal did not adequately demonstrate occupational risk for MEKP because it relied on the findings of a single 30-year-old study that described the results of animal experiments involving "novel and unusual" exposures (Ex. 3-1172, Attachment; Exs. 86 and 155; Tr. 11-265/266). In addition, this commenter stated that information is lacking as to what concentrations of MEKP currently exist in the workplace, how to measure MEKP in the occupational environment, and the feasibility of engineering controls to regulate exposures to MEKP (Ex. 3-1172, Attachment; Exs. 8-86 and 155). The Motor Vehicle Manufacturers Association (MVMA) (Ex. 3-902) merely listed MEKP as a substance for which rulemaking should be delayed; however, the MVMA provided no details in support of this comment. The New Jersey Department of Health (Ex. 144) suggested that the limits for MEKP should be derived based on EPA's IRIS data; the use of IRIS data is discussed above, in Section VI.A of the preamble.

In response to Mr. Schumacher and the National Marine Manufacturers Association (Exs. 8-86, 155, 3-1172, and 181; Tr. 11-265/266), OSHA notes that the study of MEKP's toxicity performed by Floyd and Stokinger (1958/Ex. 1-783) was a thorough and comprehensive bioassay involving three species (mice, rats, and rabbits) and five routes of exposure (inhalation, intraperitoneal, oral, dermal, and eye contact). According to the ACGIH (1986/Ex. 1-3, p. 396), this study demonstrated that MEKP was "20- to 50-fold more acutely toxic than di-t-butyl peroxide by all routes tested." The consequences of exposure to this substance ranged from skin and eye irritation to gross hemorrhage of the lung and liver and kidney damage; OSHA notes that these effects were observed even after short-term exposures. The Floyd and Stokinger study (1958/Ex. 1-783) demonstrated that MEKP is significantly more toxic than benzoyl peroxide (TLV-TWA of 5 mg/m3) and resembles hydrogen peroxide (TLV-TWA of 1.4 mg/m3) in terms of its potential to cause irritation on an acute basis. A study by Moskowitz and Grabois (1950, as cited in ACGIH 1986/Ex. 1-3, p. 54) showed that exposure to 12.2 mg/m3 benzoyl peroxide caused "pronounced irritation of the nose and throat" in workers; because MEKP is significantly more irritant than benzoyl peroxide, MEKP concentrations considerably below the 12 mg/m3 level can be expected to cause irritation as well.

Sax and Lewis (1989, p. 2312) report that MEKP is an experimental tumorigen and note that systemic effects in humans resulting from oral exposure include changes in the structure or function of the esophagus, nausea or vomiting, and other gastrointestinal effects. NIOSH (Ex. 8-47) has carefully reviewed the health effects information and the limits proposed for MEKP by OSHA. NIOSH concurs that a ceiling limit is appropriate for MEKP to protect against this substance's severe irritant effects (see Table N1 of Ex. 8-47).

With regard to Mr. Schumacher's comments concerning concentrations of MEKP in the workplace and available controls, the record contains several NIOSH health hazard evaluations and technical assistance surveys that were conducted in workplaces where MEKP was used as a reaction catalyst in polyester resin operations, the same type of operation of concern to Mr. Schumacher (NIOSH Health Hazard Evaluation Determination Report Nos. HE 79-132-673; HE 76-000-066; and HE 78-003-555). At two of the three sites surveyed, all personal and area MEKP air samples were below 1.5-mg/m3. At the third site, a total of 20 short-term samples were taken over a three-day period to determine airborne MEKP exposures during the construction of fibrous glass reinforced products utilizing the styrenemodified polyester resin sprayup process and a MEKP catalyst; eight of these short-term samples exceeded the 1.5-mg/m3 (0.2-ppm) level (NIOSH Health Hazard Evaluation Determination Report No. HE 78-003-555).

Mr. Schumacher (Ex. 155) was also of the opinion that OSHA had failed, in either the proposal or its supporting documents, to take into account the fact that a facility having multiple exposures would have to design its engineering controls to handle multiple chemicals; in the opinion of Mr. Schumacher, to control for multiple chemicals in a facility would be more expensive than controlling for a single substance. OSHA does not agree with Mr. Schumacher on either point. As discussed in Section VII of the preamble, OSHA's entire costing methodology is based on a process approach that assumes multiple chemical exposures and the use of a system of engineering controls designed to control the exposures of all employees involved in the process. OSHA believes this is a reasonable costing methodology because multiple chemicals are used at most processes. For example, in the sector of interest to Mr. Schumacher (SIC 37, Transportation Equipment), and particularly in boat-building, styrene, fiberglass, and MEKP are all used.

OSHA also conducted two site visits to MEKP-using facilities in connection with the present rulemaking (Exs. 136A and 136B). Both of the plants visited produced fiberglass boats, and personal samples were taken at both facilities for workers involved in gel-coat and lamination operations. One plant was a high-volume facility that produced approximately 24 boats per day, while the other plant produced only two to three boats per day. In the low-production facility, all MEKP sampling results for gel-coat and lamination workers were below 1.5-mg/m3 for MEKP (Ex. 136A); at the high-production facility, the single MEKP sample taken on a gel-coat operator was 3.0 mg/m3 (Ex. 136B). OSHA believes that the higher reading at the second facility is accounted for by the high rate of production at that site; controlling exposures at a high-volume facility requires the implementation of additional controls to compensate for the increase in production.

In regard to sampling and analytical methods for MEKP, OSHA notes that NIOSH has published a sampling and analytical method (PECA or 3508) for this substance and that OSHA has developed an in-house method that is available from the Agency on request; OSHA used this method without difficulty on the two site visits to MEKP-using facilities conducted for this rulemaking.

However, OSHA does find that the data in the record do not provide information that can be used to determine that 0.2 ppm (1.5 mg/m3) represents an appropriate level at which to establish the final rule PEL for MEKP. For example, the Floyd and Stokinger study reports that MEKP is "20- to 50-fold more acutely toxic than di-t-butyl peroxide by all routes tested"; however, there is no PEL or TLV for d-t-butyl peroxide for OSHA to use as a basis for the PEL. The same study notes that MEKP is significantly more toxic than benzoyl peroxide (TLV-TWA of 5 mg/m3) and resembles hydrogen peroxide in toxicity (TLV-TWA of 1.5 mg/m3) but provides no data to suggest how this "extra" toxicity might translate into a PEL. OSHA carefully reviewed the ACGIH (1986) documentation for this substance and also could find no specific basis for a ceiling of 0.2 ppm (1.5 mg/m3).

Accordingly, OSHA has concluded that, at this time, the available data support establishing a PEL for MEKP that is at least equivalent to that for benzoyl peroxide (i.e., 5 mg/m3, which is approximately equivalent to 0.7 ppm for MEKP). Given that MEKP is reported by Floyd and Stokinger to be more irritating than benzoyl peroxide and that irritation can result from even very brief exposures to excessive concentrations of MEKP, OSHA also concludes that a ceiling limit for MEKP is necessary and appropriate. Therefore, to reduce the significant risk of irritation to workers who are exposed to MEKP at higher levels, OSHA is establishing a 0.7 ppm ceiling PEL for MEKP.


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