Regulation and Risk Assessment of 1,4-Dioxane - Environmental Investigation and Remediation - page 287

TABLE 6.15
Common Occupational Exposure Standards (OESs) in the United States and Europe

Standard Acronym Defi nition

Threshold Limit Value
(United States, EU)

TLV The time-weighted average concentration of airborne substances to which

nearly all workers may be repeatedly exposed, without adverse effect

Time-Weighted Average
(United States, EU)

TWA The time-weighted average concentration for a conventional 8-hour day and

40-hour week (ACGIH and EU)

Short-Term Exposure
Limit (United States, EU)

STEL The concentration to which workers can be exposed for short periods of time,

usually 15 min, 4 times per day, without suffering adverse effects (ACGIH
and EU)

Occupational Exposure
Standard (UK)

OES The concentration of an airborne substance averaged over a reference period,

at which, according to current knowledge, there is no evidence that it is
likely to be injurious to employees, if they are exposed, by inhalation, day
after day, to that concentration (EH/40 Occupational Exposure Limits,
Health & Safety Executive, UK)

Maximum Exposure Limit
(UK)

MEL The maximum concentration of an airborne substance, averaged over a

reference period, to which employees may be exposed by inhalation under
any circumstances. Unlike the OES, there may be a residual risk to health at
this level of exposure.

Maximum Workplace
Concentration (Germany)

MAK The maximum allowable concentration of a working substance in the

workplace atmosphere as a gas, steam, or aerosol that according to current
knowledge does not impair the health of employees exposed during 8-hour
working days over the long term (German Commission for the Investigation
of Health Hazards of Chemical Compounds in the Work Area)

Maximum Workplace
Concentration
(Netherlands)

MAC The maximum concentration of a gas, steam, or aerosol of a substance in

workplace air, which when inhaled during a workday has no adverse impact
on the health of the employees (Dutch Expert Committee for Occupational
Standards, Netherlands)

Level Limit Value and
Ceiling Limit Value

LLV and CLV LLV: An occupational exposure limit value for exposure during one working

day; CLV: An occupational exposure limit value for exposure during a
reference period of 15 min (Swedish Work Environment Authority)

Permissible Exposure
Limits

PEL The legal limit for exposure of an employee to a substance, usually given as a

time-weighted average (TWA) (U.S. Occupational Safety and Health
Administration)

Occupational Exposure
Limit

OEL The maximum concentration of an airborne substance, averaged over a

reference period, to which employees may be exposed by inhalation under
any circumstances (South African Variation of UK OES)

Immediately Dangerous to
Life and Health

IDLH The limit beyond which an individual will not be capable of escaping death or

permanent injury without help in less than 30 min (U.S. NIOSH)

Minimal Risk Level MRL An estimate of the daily human exposure to a hazardous substance that is

likely to be without appreciable risk of adverse noncancer health effects over
a specii ed duration of exposure (U.S. ATSDR)

Notes: ACGIH, American Conference of Governmental Industrial Hygienists; EU, European Union; and UK, United Kingdom.

Regulation of 1,4-dioxane emissions varied by industry and by state. For example, vapor degreas-
ing operations, a major source of 1,4-dioxane emissions, were regulated by the National Emission
Standards for Halogenated Solvent Cleaning (40 CFR, 63.460 through 63.469). Local air pollution
control districts inspect and enforce standards on degreasing operations to control solvent emissions.
After 1998, wood furniture-manufacturing facilities releasing more than 1200 pounds of 1,4-dioxane
per year must report emissions and track annual usage (USEPA, 1998b). California's Toxic Hot