Threshold limit value
≈ 7 min read
Names in other languages
No names in other languages are held for this entry yet.
Article bodies are English and are not machine-translated. A name in another language is not a translation of the article.
The threshold limit value (TLV) is a level of occupational exposure to a hazardous substance where it is believed that nearly all healthy workers can repeatedly experience at or below this level of exposure without adverse effects. Strictly speaking, TLV is a reserved term of the American Conference of Governmental Industrial Hygienists (ACGIH), who determines and publishes TLVs annually. TLVs issued by the ACGIH are the most widely accepted occupational exposure limits both in the United States and most other countries. However, it is sometimes loosely used to refer to other similar concepts used in occupational health and toxicology, such as acceptable daily intake (ADI) and tolerable daily intake (TDI). Concepts such as TLV, ADI, and TDI can be compared to the no-observed-adverse-effect level (NOAEL) in animal testing, but whereas a NOAEL can be established experimentally during a short period, TLV, ADI, and TDI apply to human beings over a lifetime and thus are harder to test empirically and are usually set at lower levels. TLVs, along with biological exposure indices (BEIs), are published annually by the ACGIH. The TLV is an estimate based on the known toxicity in humans or animals of a given chemical substance, and the reliability and accuracy of the latest sampling and analytical methods.…
The threshold limit value (TLV) is a level of occupational exposure to a hazardous substance where it is believed that nearly all healthy workers can repeatedly experience at or below this level of exposure without adverse effects. Strictly speaking, TLV is a reserved term of the American Conference of Governmental Industrial Hygienists (ACGIH), who determines and publishes TLVs annually. TLVs issued by the ACGIH are the most widely accepted occupational exposure limits both in the United States and most other countries. However, it is sometimes loosely used to refer to other similar concepts used in occupational health and toxicology, such as acceptable daily intake (ADI) and tolerable daily intake (TDI). Concepts such as TLV, ADI, and TDI can be compared to the no-observed-adverse-effect level (NOAEL) in animal testing, but whereas a NOAEL can be established experimentally during a short period, TLV, ADI, and TDI apply to human beings over a lifetime and thus are harder to test empirically and are usually set at lower levels. TLVs, along with biological exposure indices (BEIs), are published annually by the ACGIH. The TLV is an estimate based on the known toxicity in humans or animals of a given chemical substance, and the reliability and accuracy of the latest sampling and analytical methods. TLVs do not take into account financial or technical feasibility for application in the workplace, instead solely focusing on health based recommendations to prevent adverse health effects. It is also not a static value, since new research can often modify the risk assessment of substances, and new laboratory or instrumental analysis methods can improve analytical detection limits. The TLV is a recommendation by ACGIH, with only a guideline status. As such, it should not be confused with exposure limits having a regulatory status, like those published and enforced by the Occupational Safety and Health Administration(OSHA). However, many OSHA exposure limits are not considered by the industrial hygiene community to be sufficiently protective levels since the toxicological basis for most limits have not been updated since the 1960s. OSHA acknowledges this and recommends supplementing regulatory standards with alternative updated and stricter standards, "even when the exposure levels are in compliance with the relevant PELs", while specifically mentioning the TLV as one such standard. The TLV for chemical substances is defined as a concentration in air, typically for inhalation or skin exposure. Its units are in parts per million (ppm) for gases and in milligrams per cubic meter (mg/m 3 ) for particulates such as dust, smoke and mist. The basic formula for converting between ppm and mg/m 3 for gases is ppm = (mg/m^3) * 24.45 / molecular weight. This formula is not applicable to airborne particles. The four categories of TLVs for chemical substances are defined: Threshold limit value − time-weighted average (TLV-TWA): The average exposure on the basis of a 8 hours per day, 40 hours per week work schedule. Threshold limit value − short-term exposure limit (TLV-STEL): A 15-minute TWA exposure that should not be exceeded at any time during a workday, even if the 8-hour TWA is within the TLV-TWA. Threshold limit value - surface limit (TLV-SL): Supplements airborne TLVs by establishing a concentration on a surface that is not likely to cause an adverse effect due to direct or indirect contact. Threshold limit value − ceiling limit (TLV-C): An absolute exposure limit that should not be exceeded at any time. There are TLVs for physical agents as well as chemical substances. TLVs for physical agents include those for noise exposure, vibration, ionizing and non-ionizing radiation exposure and heat and cold stress.
Defining acceptable exposure
The TLV and most other occupational exposure limits are based on available toxicology and epidemiology data to protect nearly all workers over a working lifetime. Exposure assessments in occupational settings are most often performed by Occupational / Industrial Hygiene (OH/IH) professionals who gather "Basic Characterization" consisting of all relevant information and data related to workers, agents of concern, materials, equipment and available exposure controls. The exposure assessment is initiated by selecting the appropriate exposure limit averaging time and "decision statistic" for the agent. Typically the statistic for deciding acceptable exposure is chosen to be the majority (90%, 95% or 99%) of all exposures to be below the selected occupational exposure limit. For retrospective exposure assessments performed in occupational environments, the "decision statistic" is typically a central tendency such as the mean or geometric mean or median for each worker or group of workers. Methods for performing occupational exposure assessments can be found in "A Strategy for Assessing and Managing Occupational Exposures, Third Edition Edited by Joselito S. Ignacio and William H. Bullock".
Similar concepts
The TLV is equivalent in spirit to various occupational exposure limits developed by organizations around the world; however, the materials covered, values recommended, and definitions used can differ amongst organizations. These occupational exposure limits include:
Other countries
Australia OES Occupational exposure standard Austria TRK (Technische Richtkonzentration trans. Technical Approximate Concentration ) MAK (Maximale Arbeitsplatz-Konzentration trans. Maximum Workplace Concentration) Brazil LT (Limite de tolerância) France VME (Valeur Moyenne d'Exposition) VLE (Valeur Limite d'Exposition) Germany AGW (Arbeitsplatzgrenzwert trans. Workplace Limit Value) MAK (Maximale Arbeitsplatz-Konzentration trans. Maximum Workplace Concentration) Indonesia NAB (Nilai ambang batas) Malaysia PEL (Permissible exposure limit) Netherlands MAC (Maximaal Aanvaardbare Concentratie trans. Maximum Acceptable Concentration) New Zealand WES (Workplace Exposure Standards) Poland NDS (Najwyższe dopuszczalne stężenie) Russia ПДК (предельно допустимая концентрация) Spain VLA (Valor Límite Ambiental) UK WEL (Workplace Exposure Limit) Ukrainian ГДК (Гранично допустима концентрація)
Antonymic concepts
The opposite of "safe enough for any length of time" is "not safe for any length of time", and IDLH values are defined for concentrations of substances that are immediately dangerous to life or health.
References
de:Arbeitsplatzgrenzwert tr:Eşik sınır değeri
Text derived from https://en.wikipedia.org/w/index.php?oldid=1378527110 under CC BY-SA 4.0; modifications have been made.