Threshold limit value

Threshold limit value

The threshold limit value (TLV) of a chemical substance is a level to which it is believed a worker can be exposed day after day for a working lifetime without adverse health effects. Strictly speaking, TLV is a reserved term of the American Conference of Governmental Industrial Hygienists (ACGIH). However, it is sometimes loosely used to refer to other similar concepts used in occupational health and toxicology. 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. It is not a static definition 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). The OSHA regulatory exposure limits permissible exposure limits (PELs) published in 29CFR 1910.1000 Table Z1 are based on recommendations made by the ACGIH in 1968, although other exposure limits were adopted more recently. Many OSHA exposure limits are not considered by the industrial hygiene community to be sufficiently protective levels. The National Institute of Occupational Safety and Health (NIOSH) publishes recommended exposure limits (RELs) which OSHA takes into consideration when promulgating new regulatory exposure limits.

Definitions

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/m³) for particulates such as dust, smoke and mist. The basic formula for converting between ppm and mg/m³ for gases is ppm = (mg/m^3) * 24.45 / molecular weight. This formula is not applicable to airborne particles.

Three types of TLVs for chemical substances are defined:

  1. Threshold limit value - Time weighted average (TLV-TWA): average exposure on the basis of a 8h/day, 40h/week work schedule
  2. Threshold limit value - Short-term exposure limit (TLV-STEL): spot exposure for a duration of 15 minutes, that cannot be repeated more than 4 times per day
  3. Threshold limit value - Ceiling limit (TLV-C): 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.

Similar concepts

The TLV is equivalent in spirit, although the materials covered, values recommended, and definitions used can differ, to the following concepts.

  • WEEL (Workplace environmental exposure level) created by a committee of the American Industrial Hygiene Association AIHA

Similar concepts used in other countries include:


Wikimedia Foundation. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Threshold Limit Value — Time Weighted Average (TLV TWA, Valor Límite Umbral Media Ponderada en el Tiempo o Telematicamente Limites Umbral). Contenido 1 Definición 2 Conceptos similares 3 Véase también 4 …   Wikipedia Español

  • Threshold Limit Value — The Threshold Limit Value (TLV) of a chemical substance is a level to which it is believed a worker can be exposed day after day for a working lifetime without adverse health effects. Strictly speaking, TLV is a reserved term of the American… …   Wikipedia

  • Threshold Limit Value - Time Weighted Average — Saltar a navegación, búsqueda Threshold Limit Value Time Weighted Average (TLV TWA, Valor Límite Umbral Media Ponderada en el Tiempo). Valor límite ambiental publicado por la A.C.G.I.H. (American Conference of Governmental Industrial Hygienists); …   Wikipedia Español

  • threshold limit value — (TLV) a value assigned to an industrial chemical by the American Conference of Governmental Hygienists, representing the maximum concentration to which most workers can be repeatedly exposed without adverse health effects …   Medical dictionary

  • value — A particular quantitative determination. For values not given below, see the specific name. SEE ALSO: index, number. [M.E., fr. O.Fr., fr. L. valeo, to be of v.] acetyl v. the milligrams of KOH required to neutralize the acetic acid produced by… …   Medical dictionary

  • Occupational exposure limit — An occupational exposure limit is an upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. It is typically set by competent national authorities and enforced by… …   Wikipedia

  • Threshold braking — or limit braking is a driving technique most commonly used in motor racing, but also practised in road vehicles to slow a vehicle at the optimum rate using the brakes. This is mostly used in vehicles without an anti lock braking system fitted,… …   Wikipedia

  • Value Added Tax-free Exports from the Channel Islands — are exports of goods from the Channel Islands on which value added tax (VAT) is not levied. In recent years, companies in the United Kingdom have expressed concern at the competition thereby offered to their goods on which VAT is… …   Wikipedia

  • threshold — 1. The point at which a stimulus first produces a sensation. 2. The lower limit of perception of a stimulus. 3. The minimal stimulus that produces excitation of any structure; e.g., the minimal stimulus eliciting a moto …   Medical dictionary

  • threshold — 1. A quantifiable limit beyond which the nature of an item changes. For example, a taxation threshold is a point at which a *tax rate changes. 2. A quantifiable limit used in the establishment of *internal controls over *authorization procedures …   Auditor's dictionary

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”