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At least 19 recordsLinked to original sources
PubMed1990

But they are not thresholds: a critical analysis of the documentation of Threshold Limit Values.

Threshold Limit Values (TLVs) represent conditions under which the TLV Committee of the American Conference of Governmental Industrial Hygienists (ACGIH) believes that nearly all workers may be repeatedly exposed without adverse effect. A detailed research was made of the references in the 1976 Documentation to data on "industrial experience" and "experimental human studies." The references, sorted for those including both the incidence of adverse effects and the corresponding exposure, yielded 158 paired sets of data. Upon analysis it was found that, where the exposure was at or below the TLV, only a minority of studies showed no adverse effects (11 instances) and the remainder indicated that up to 100% of those exposed had been affected (8 instances of 100%). Although, the TLVs were poorly correlated with the incidence of adverse effects, a surprisingly strong correlation was found between the TLVs and the exposures reported in the corresponding studies cited in the Documentation. Upon repeating the search of references to human experience, at or below the TLVs, listed in the more recent, 1986 edition of the Documentation, a very similar picture has emerged from the 72 sets of clear data which were found. Again, only a minority of studies showed no adverse effects and TLVs were poorly correlated with the incidence of adverse effect and well correlated with the measured exposure. Finally, a careful analysis revealed that authors' conclusions in the references (cited in the 1976 Documentation) regarding exposure-response relationships at or below the TLVs were generally found to be at odds with the conclusions of the TLV Committee. These findings suggest that those TLVs which are justified on the basis of "industrial experience" are not based purely upon health considerations. Rather, those TLVs appear to reflect the levels of exposure which were perceived at the time to be achievable in industry. Thus, ACGIH TLVs may represent guides of levels which have been achieved, but they are certainly not thresholds.

Air Pollutants, Occupational↗
PubMed1986

Identification and classification of carcinogens: procedures of the Chemical Substances Threshold Limit Value Committee, ACGIH. American Conference of Governmental Industrial Hygienists.

The Chemical Substances Threshold Limit Value Committee of the American Conference of Governmental Industrial Hygienists has refined its procedures for evaluating carcinogens. Types of epidemiologic and toxicologic evidence used are reviewed and a discussion is presented on how the Committee evaluates data on carcinogenicity. Although it has not been conclusively determined whether biological thresholds exist for all types of carcinogens, the Committee will continue to develop guidelines for permissible exposures to carcinogens. The Committee will continue to use the safety factor approach to setting Threshold Limit Values for carcinogens, despite its shortcomings. A compilation has been developed for lists of substances considered to be carcinogenic by several scientific groups. The Committee will use this information to help to identify and classify carcinogens for its evaluation.

Carcinogens↗
PubMed1988

Corporate influence on threshold limit values.

Investigations into the historical development of specific Threshold Limit Values (TLVs) for many substances have revealed serious shortcomings in the process followed by the American Conference of Governmental Industrial Hygienists. Unpublished corporate communications were important in developing TLVs for 104 substances; for 15 of these, the TLV documentation was based solely on such information. Efforts to obtain written copies of this unpublished material were mostly unsuccessful. Case studies on the TLV Committee's handling of lead and seven carcinogens illustrate various aspects of corporate influence and interaction with the committee. Corporate representatives listed officially as "consultants" since 1970 were given primary responsibility for developing TLVs on proprietary chemicals of the companies that employed them (Dow, DuPont). It is concluded that an ongoing international effort is needed to develop scientifically based guidelines to replace the TLVs in a climate of openness and without manipulation by vested interests.

Acrylonitrile↗
PubMed1990

[UV exposure in the workplace. Apropos the establishing of threshold limit values].

Although UV exposure is present at many workplaces, it has not gained much attention. Particularly with regard to UVA, the UV threshold limit values for acute effects used to date are insufficient, and there are no obligatory limits to prevent the sequels of chronic UV exposure. More precise threshold limit values have been published only preliminarily (DIN-Standard No. 5031, part 10). There is a need for regulations governing the supervision of occupational UV exposure and the individual protection of exposed persons.

Dose-Response Relationship, Radiation↗
PubMed2001

A critical evaluation of the scientific basis of the MAK Commission's new general threshold limit values for dust.

In 1997, the German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area set a new MAK value ("Maximale Arbeitsplatz-Konzentration") governing worker exposures to general airborne dust. The new values limit worker dust exposures to concentrations not exceeding 1.5 mg/m3 for respirable dust and 4 mg/m3 for inhalable dust, and are substantially lower than corresponding standards in other western industrialized nations. The purpose of this document is to critically review the science behind the MAK Commission's new threshold limit value standards. The Commission relied heavily upon a re-analysis of data from the Deutsche Forschungsgemeinschaft (DFG) Chronic Bronchitis study (1965-1977). We have reservations about the scientific merit of the DFG study and the validity of data used as the basis for establishing a new MAK value for dust. In particular: (1) Assessing the potential role of inert dust in the development of chronic bronchitis in worker cohorts with extremely high cigarette smoking prevalences is scientifically implausible. (2) It is unlikely that the dust in the industries studied, including steel works, foundries and cement works, was in fact "inert", and any effects of the dust on chronic bronchitis rates may have been increased by the presence of free crystalline silica and other toxic agents. (3) The study made use of area- rather than personal-exposure monitoring, thereby correlating the prevalence of chronic bronchitis with lower dust exposure levels than actually existed and significantly overstating the health effects of the dust exposures. (4) Inappropriate statistical methods were used to estimate threshold limit values. Results of three additional epidemiological studies are cited as providing evidence of chronic lung effects due to insoluble dust exposure. All three studies suffer from extremely poor documentation of the study methodology, particularly regarding lung function testing, and they provide little evidence that exposure to insoluble non-fibrogenic dusts leads to chronic lung obstruction. In summary, it is our opinion that the studies evaluated by the MAK Commission and the methods used do not provide the scientific basis to support the lower threshold limit values for dust. We recommend that an appropriate prospective morbidity study be conducted to address the concerns detailed in this critical examination.

Bronchitis↗
PubMed1984

The origin and basis of threshold limit values.

The concept of establishing a "threshold limit" for contaminants of industrial air is based on the principles of establishing: (1) quantitative relationships between the magnitude and duration of exposure to an industrial substance and the nature and magnitude of the response of the worker, and (2) a limiting level of exposure to potentially hazardous agents, when there exists no significant threat to health. This paper focuses on the origin of this concept, and traces the history and development of thought concerning the founding principles upon which it is based. The TLVs have undergone a remarkable evolution, from values denoting concentrations of contaminant producing overt signs of acute toxicity, to those concentrations to which nearly all workers may be exposed for their working lifetime without experiencing adverse health effects.

Environmental Exposure↗
PubMed1992

The role of threshold limit values in U.S. air pollution policy.

This paper analyzes the role of threshold limit values (TLVs) in national air pollution policy during the 1980s, a period in which the Environmental Protection Agency (EPA) sought to delegate to individual states the authority to evaluate and regulate airborne toxic substances. We focus on 20 carcinogens and 11 substances with non-genotoxic health effects that were regulated by local air toxics programs using TLVs. Data from EPA's National Air Toxics Information Clearinghouse indicate that maximum TLV-based Ambient Air Level guidelines (AALs) frequently exceed minimum TLV-based AALs by a factor of greater than 1,000. Cancer potency data from EPA's Integrated Risk Information System suggest significant risks remain at TLV-based AALs. Cancer risks at the median TLV-based AAL exceed 1,000 cases per million exposed persons for cadmium (1,040), nickel and its compounds (1,420), propylene oxide (1,550), coke oven emissions (1,860), benzene (2,500), arsenic and its compounds (7,300), N-nitrosodimethylamine (21,000), asbestos (21,500), and ethylene dibromide (55,000). We also summarize published studies that report non-genotoxic health effects in workers exposed at levels near the TLV for 11 substances whose AALs were based on TLVs. Contrary to the assumption frequently made by state air toxics program, TLVs cannot be taken to represent no observed effect levels (NOELs) for regulatory purposes.

Acrylonitrile↗
PubMedDate not supplied

An analysis of the implications of a magnetic field threshold limit value on utility work practices.

This article examines the implications of a 10 gauss (G) occupational threshold limit value (TLV) on the work practices of a utility that must maintain and repair 500 and 230 kV transmission lines. Three work practices are compared: bare-handed work with live lines (the current practice at the example utility), use of hot sticks, and de-energizing lines prior to work. Bare-handed work with live lines leads to occasional exceedances of the 10 G TLV. Use of hot sticks and de-energizing lines eliminate these exceedances, but they do so at a price. Both practices increase the job duration and, as a result, may increase occupational injury risks. The annual costs for the current live-line, bare-handed practice is approximately $175,000. Use of hot sticks increases this annual cost of maintenance and repair by 30 to 55%. De-energizing lines can increase annual costs by $4 million to $14 million, due to the need for adding additional electricity generation during the planned outages. De-energizing lines also increases the risk to service reliability slightly.

Costs and Cost Analysis↗
PubMed1983

Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution.

The body of information in this paper is directed to specialists in industrial health and safety, and air and water pollution, who need quantitative data on the odor thresholds of potentially hazardous chemical vapors and gases. The literature, largely unorganized, has been reviewed for 214 compounds and condensed into tables based on consistent units. Data on the volatility, solubility, ionization and water-air distribution ratio at 25 degrees C are included. From the currently recommended threshold limit value (TLV), a safe dilution factor and an odor safety factor are calculated for each compound. The equivalent data are presented for both air and water dilutions of the chemicals. Available data are summarized on the variability of odor sensitivities in the population, and the increased odor concentrations that are required to elicit responses from persons whose attention is distracted, or who are sleeping. This information is reduced to calibration charts that may be used to estimate the relative detectability, warning potential and rousing capacity of the odorous vapors. Each compound has been assigned a letter classification, from A to E, to indicate the margin of safety, if any, that may be afforded by the odor of the compound as a warning that its threshold limit value is being exceeded.

Environmental Exposure↗
PubMed1997

Metal fume fever: characterization of clinical and plasma IL-6 responses in controlled human exposures to zinc oxide fume at and below the threshold limit value.

Results from animal and preliminary human exposure studies have called into question whether the 5 mg/m3 8-hour time-weighted average threshold limit value (TLV) for zinc oxide fume is sufficient to protect workers against metal fume fever. The objectives of this study were to determine the clinical effects of exposures to low concentrations of zinc oxide and to ascertain whether these exposures elevated circulating levels of specific cytokines, which could account for the symptoms of the metal fume fever syndrome. Thirteen resting naive subjects inhaled, on separate days, air and 2.5 and 5 mg/m3 of furnace-generated zinc oxide fume for 2 hours. Subjects recorded symptoms and temperature and had blood drawn before and after each exposure. The mean (+/- SE) maximum rise in oral temperature at 6 to 12 hours after exposure was 1.4 +/- 0.3 degrees F after 5 mg/m3, compared with 0.6 +/- 0.5 degrees F after air exposure (P < 0.05). Mean temperature was also elevated after exposure to 2.5 mg/m3 zinc oxide (1.2 +/- 0.3 degrees F). In a parallel fashion, plasma levels of interleukin 6 (IL-6), a pyrogen, were significantly elevated after exposure to 5 mg/m3 zinc oxide. Mean IL-6 values (pg/mL) at pre-exposure and at 3 and 6 hours post-exposure were 1.9 (+/- 0.6), 2.8 (+/- 0.7), and 2.9 (+/- 0.6), respectively, on the air day and 1.6 (+/- 0.6), 4.4 (+/- 1.2), and 6.4 (+/- 1.1) on the 5 mg/m3 zinc oxide day. Zinc oxide exposure did not significantly affect plasma levels of tumor necrosis factor. Total symptom scores peaked 9 hours after the 5 mg/m3 zinc oxide exposure. Myalgias, cough, and fatigue were the predominant symptoms reported. Inhalation of zinc oxide for 2 hours at the current TLV of 5 mg/m3 produces fever and symptoms along with elevation in plasma IL-6 levels.

Adult↗
PubMed1995

The origin and development of the asbestos Threshold Limit Value: scientific indifference and corporate influence.

Several recent articles have critiqued the process employed by the American Conference of Governmental Industrial Hygienists in determining Threshold Limit Values. Criticisms have included inadequate data collection, inadequate research, excessive corporate influence, and slow response to informational changes. In this article, the authors address the historical development of the American Conference of Governmental Industrial Hygienists' asbestos exposure guideline. They demonstrate that the proposed guideline was known to be inadequate when it was first proposed, was severely criticized between 1946 and 1968, but nonetheless was promulgated annually and remained unchanged 1971.

Asbestos↗
PubMed1995

Toluene diisocyanate induction of airway hyperresponsiveness at the threshold limit value (10 ppb) in rabbits.

Induction of acute lung injury and the development of airway hyperresponsiveness (AHR) by toluene diisocyanate (TDI) exposure was studied in a new rabbit model of occupational lung diseases. TDI in the range of the threshold limit value (TLV) of 10 ppb, as well as at 5 and 30 ppb, administered four times over a period of 1 h to three groups of eight rabbits, did not significantly alter airway resistance (RI), dynamic elastance (Edyn), slope of inspiratory pressure generation (delta Pes/tI), arterial pressure (Pa) or arterial blood gas tensions (PaO2, PaCO2). Airway responsiveness (AR) to aerosols of 2% acetylcholine (ACH) was measured before and after each TDI exposure. After TDI inhalation of 10 ppb over 4 h, the amplitude of the ACH-induced airway constrictor response indicated by the changes in Edyn rose significantly to almost twice the control response value (p < 0.005). Similar changes in the amplitude of RI and in the slope of delta Pes/tI were obtained. After inhalation of 5 ppb TDI, no changes in airway reactivity were observed. The responses of respiratory mechanical parameters to ACH rose to three to four times the control responses after exposure to 30 ppb TDI. In a control group of eight animals not undergoing TDI exposure, no significant changes of respiratory responses were obtained after inhalation of 0.2% ACH for 1 min. In summary, TDI atmospheres in the range of TLV increased AR to ACH within 4 h of exposure in this rabbit model. This augmented AR may indicate an increased risk for the development of isocyanate-induced obstructive lung diseases.

Acetylcholine↗
PubMed1993

Threshold limit values, permissible exposure limits, and feasibility: the bases for exposure limits in the United States.

The development of exposure limits in the United States has always relied heavily upon the threshold limit values (TLVs) developed by the American Conference of Governmental Industrial Hygienists (ACGIH). In fact, the TLVs were adopted as official exposure limits by the Occupational Safety and Health Administration (OSHA) in 1972 and 1989. Given the continuing importance of the ACGIH limits, this paper compares the basis of the TLVs with that employed by OSHA de novo in its 12 new permissible exposure limits (PELs). Using benzene as an example, it is shown that OSHA's new PELs have been established following a rigorous assessment of the inherent risks and the feasibility of instituting the limit. The TLVs, on the other hand, have been developed by ad hoc procedures and appear to have traditionally reflected levels thought to be achievable at the time. However, this might be changing. Analysis of the historical reductions of TLVs, for 27 substances on the 1991-1992 list of intended changes, indicates smaller reductions in the past (median reduction of 2.0-2.5-fold between 1946 and 1988) compared to those currently being observed (median reduction of 7.5-fold between 1989 and 1991). Further analysis suggests a more aggressive policy of the ACGIH regarding TLVs for carcinogens but not for substances that produce effects other than cancer. Regardless of whether the basis of the TLVs has changed recently, it would take a relatively long time for the impact of any change to be felt, since the median age of the 1991-1992 TLVs is 16.5 years, and 75% of these limits are more than 10 years old. The implications of OSHA's continued reliance on the TLVs as a means of updating its PELs are discussed, and four alternatives are presented to the ACGIH regarding the future of its activities related to exposure limits. It is concluded that new mechanisms are needed for OSHA to update its PELs in a timely fashion so that the TLVs will not be adopted by default in the future.

Air Pollutants, Occupational↗
PubMed1977

Proposed biological threshold limit values for industrial exposure to trichloroethylene vapor.

A model was used for the simulation of the pharmacokinetics of inhaled trichloroethylene (TRI) vapor. Computed data of TRI in alveolar air and of trichloroacetic acid (TCA) and trichloroethanol (TCE) in blood and urine agreed satisfactorily with experimental results obtained by various authors. Biological threshold limit values were calculated for subjects exposed at rest to a steady concentration of 100 ppm of TRI in ambient air, between 0800 and 1200 and between 1300 and 1700, five days week during the whole year. The Monday to Friday range of values for urinary excretion (243--322 mg of TCA/24 h and 288--429 mg of TCE/24 h) roughly corresponded to the findings of several surveys among TRI workers in industry. The hypnotic effect of TCE and/or TRI during steady or fluctuating industrial TRI exposure was discussed with the aid of the model.

Chloral Hydrate↗
PubMed1994

Sensory irritation and pulmonary irritation of n-methyl ketones: receptor activation mechanisms and relationships with threshold limit values.

Activation of the trigeminal nerve endings in eyes and nose, termed sensory irritation, was determined from the reflexively induced decrease in respiratory rate in mice for methyl propyl ketone, methyl butyl ketone, methyl amyl ketone and methyl hexyl ketone. The relationship between exposure concentration and the decrease in respiratory rate followed Michaelis-Menten equations. Two estimates of each agonist-receptor dissociation constant were obtained, one from the Michaelis-Menten equation and one from the threshold (RD-0) of the log concentration-effect curve. The values were equal and thus one receptor type could account for the activation process. The hydrophobic properties of the receptor biophase were found to approach that of the internal part of the bilayer membrane. It therefore follows that the receptor-air partition coefficients increase with the size of the ketones, thus accounting for the observed increase in potency. Estimates of Threshold Limit Values (TLV) were obtained and compared with established values. Close agreements were found for methyl propyl ketone and methyl amyl ketone, but not for methyl butyl ketone, where the neurotoxic effect constituted a more sensitive endpoint than sensory irritation.

Administration, Inhalation↗