Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 286

and vapor density account for its potential to travel considerable distances to an ignition source with
a consequent risk of “l ash back.” The accident that killed the welder working on the space shuttle
solid rocket booster casings (described in Section 1.2.2.1) serves as a grim reminder of the hazard
that 1,4-dioxane, nitromethane, and other l ammable stabilizers can pose to workers who handle
these chemicals.
As described in Chapter 4, 1,4-dioxane can form explosive peroxide crystals on the threads of
screw cap bottles. 1,4-Dioxane may also react vigorously with oxidizing agents. Risks from
products containing 1,4-dioxane as an ingredient depend on the physicochemical properties of
other ingredients present in the product and should be determined for the mixture as a whole
(NICNAS, 1998).
Regulation of 1,4-dioxane as a workplace inhalation hazard and as a toxic air contaminant is
reviewed in the remainder of this section.
6.3.1 O CCUPATIONAL H EALTH AND S AFETY R EGULATIONS FOR 1,4-D IOXANE
As described in Section 6.5.3 , occupational use of 1,4-dioxane or work at facilities that produce
1,4-dioxane as a by-product creates the greatest potential for inhalation exposure to 1,4-dioxane.
Beginning in the late 1970s, major advances were made in worker health and safety regulations
and practices in the United States and other developed nations. Today, the likelihood of exposure
is greatly diminished, if not eliminated, because methyl chloroform was banned in the 1990
Montreal Protocol.
A variety of regulations have been promulgated by health and labor agencies to ensure that expo-
sure to airborne contaminants in the workplace is controlled to prevent adverse health effects.
Regulations establish safe exposure levels. The wide variety in established exposure levels rel ects
differences in the time period for the measurement, the underlying toxicity values upon which the
exposure limits are based, and the safety factor applied. Regulatory bodies throughout the world use
exposure standards including the Threshold Limit Value (TLV), Occupational Exposure Standard
(OES), Maximum Exposure Limit (MEL), maximum allowable concentration (MAK), and Short-
Term Exposure Limit (STEL). The common convention for an exposure period is either an 8-hour
workday for chronic toxins or a 15-minute exposure period for acute toxins. Table 6.15 provides
dei nitions for the common exposure standards, and Table 6.16 lists inhalation exposure limits
developed for 1,4-dioxane. Figure 6.1 presents a graphical comparison of health limits and regula-
tory advisory thresholds for inhalation of 1,4-dioxane.
6.3.2 E MISSIONS S TANDARDS AND A IR Q UALITY R EGULATIONS FOR 1,4-D IOXANE
1,4-Dioxane is designated as a hazardous air pollutant in Title 42, Public Health and Welfare,
Chapter 85, on Air Pollution Prevention and Control. As early as 1978, 1,4-dioxane was recognized
in New Jersey as among the top eight air pollutants for which emission reductions through regula-
tion were necessary, together with benzene, carbon tetrachloride, chloroform, ethylene amine,
ethylene dibromide, tetrachloroethylene, and TCE ( Chemical Week , 1978).
Most ambient air quality monitoring programs do not monitor for 1,4-dioxane; however, there
are many indications that it was likely to be present in solvent-polluted air in air basins with signii -
cant industrial activity. In 1999, 1,4-dioxane was ranked as 14th among 40 priority pollutants by the
California Air Resources Board (Kyle et al., 2001; Cal EPA, 1999).
Figure 2.5a and b in Chapter 2 present annual atmospheric emissions of 1,4-dioxane from
industrial operations reported in USEPA's Toxic Release Inventory. The average emissions of 1,4-
dioxane across the United States from 1988 through 2004 was more than 300,000 pounds/year; in
1999, annual 1,4-dioxane emissions in California were estimated to be about 150,000 pounds
(CARB, 2008).