Intra-workday fluctuations of airborne contaminant concentration and the time-weighted average

Air contaminant concentrations vary between and within workdays and are often measured across a workday by passing a known air volume through a collection device. Laboratory analysis determines the contaminant mass trapped, providing a time-weighted average air concentration (C_TWA). This approach was driven by the best technologies available as exposure measurement processes developed and accuracy and measurement precision were sought. However, all integrated concentration•time (C•t) values determining C_TWA are equally weighted in assessing exposures, intra-workday concentration variability is unknown, and results are available days later. At times inappropriately, an occupational exposure limit (OEL) expressed as a C_TWA also requires equal weighting of all C•t values across an exposure period following concepts of Haber's law. Continuous monitoring (real-time detection) informs both the C_TWA and the variability of C during sampling, which are needed for stressors where a ceiling or peak OEL exists, for dangerous exposures to permanent gas-type contaminants, and for immediately dangerous to life or health (IDLH) conditions. Selective and accurate real-time detection instruments are not available for all air contaminants, but exposure magnitude information may be provided. The large amounts of data from continuous monitoring and the ability to correlate exposure maxima to specific tasks are also important. An exposure assessment role exists for selective and nonselective monitors, and in some cases, similar accuracy and precision are provided compared to laboratory analyses. Continuous monitoring may be of value when the alternative is the collection of a few C_TWA data points. Digitized personal monitor data can support the automation of some exposure control decisions or allow such decisions to be made by people in near real-time. The emerging Internet of Things (IoT) offers opportunities to integrate digital exposure data into decision-making to increase both efficiency and safety. The perceived and real uncertainty associated with real-time exposure assessments may be lessened with work to rule out the presence of know interferents and confirm the presence of target analytes.

Hydrogen Sulphide (H2S) Exposure Hazard Assessment: An Algorithm for Generating Exposure Index Based on Direct Instrument Readings

OBJECTIVES

Increased use of small affordable alarm sensors with logging or network capabilities has improved the ability to monitor exposure. The large datasets generated from these monitors calls for development of a computer algorithm to assess these data.

METHODS

We examined 88 time series of hydrogen sulphide (H2S) from wastewater works previously used for developing the exposure index. The time series covered 331 h, where 16 h had readings different from zero.

RESULTS

The developed algorithm reproduced the manual assessed index almost perfectly (linear regression β = 1.02, R2 = 0.97, P < 0.001). Time-weighted average (TWA) values of the 88 time series showed a mean value of 0.04 ppm (range 0.0-0.9). The mean index value was 18 (range 0-337), with a good linear fit (β = 0.002, R2 = 0.93, and P < 0.001). The index gave us a better resolution and basis for risk assessment than the TWA, and managed to combine evaluation of TWA and exceedance of ceiling value in one number.

CONCLUSIONS

As long as peaks above ceiling value occur, we find alarm tools with an H2S sensor to be an essential personal protective equipment against H2S. The proposed method has been verified, and it removes some common human errors in graph evaluation. Use of the index is a possible way of quantifying risk level in exposure to H2S in one single number and provides better understanding of the risk of exposure, as it eases the analysis and evaluation of large numbers of time series.

Field Evaluation of the Ultrasonic Personal Aerosol Sampler (UPAS) for Respirable Dust Exposure in a Taconite Mine

Exposure to respirable dust (RD; the mass fraction of inhaled particles that penetrate to the unciliated airways) is a major health concern in a variety of workplaces. While the estimation of personal exposure is an essential step in protecting worker health from aerosol hazards, the traditional method for assessing personal exposure to RD, suggested by the National Institute for Occupational Safety and Health (NIOSH method 0600), requires equipment that is heavy, bulky, noisy, and has the need of frequent calibration. The ultrasonic personal aerosol sampler (UPAS) is a new personal sampling technology designed to address some of these drawbacks associated with traditional sampling methods. In this study, we field tested and evaluated the performance of the UPAS for assessing worker exposure to RD in a taconite mine. Mineworkers (n = 39) from various job categories were recruited to wear both UPAS and NIOSH 0600 samplers on a work vest to estimate time-weighted exposure to RD. A strong linear relationship was observed (NIOSH method 0600 = 1.06 (UPAS) -9.22 µg m-3, r2 of 0.72, and Pearson correlation coefficient of 0.854). None of the workers were exposed to a RD concentration above the Occupational Safety and Health Administration permissible exposure limit (5 mg m-3). A Bland-Altman analysis revealed that 72% of the valid UPAS samples agreed within ±25% of the traditional method mean. The impact of job category on the correlation of the methods was not statistically significant. This work suggests that the UPAS may present a viable alternative for assessing personal exposure to RD in the workplace.

Application of a Solid Ceramic Membrane for Monitoring Volatile Organic Compounds in Industrial Wastewater

A large quantity of volatile organic compounds (VOCs) can be released into water environments from oil spills and chemical exposure accidents. A recently developed solid ceramic dosimeter (SCD) could be used for long-term measuring of low VOCs concentrations in water. However, calibration and field testing of these SCDs have thus been far insufficient to apply for VOCs monitoring in a water environment in a chemical industrial area. We conducted laboratory calibration experiments and stability tests of the SCD. The mass accumulation of 14 target VOCs from 2 to 100 μg/L was increased linearly with time in the sampler. The absorption rate of the VOCs was related to Henry's law constant. The average diffusion coefficient of the 14 VOCs in the SCD wall was 1.02 × 10^-9 m²/s. The SCD was utilized in a petrochemical plant complex in South Korea with an industrial wastewater reservoir. After a total of 7 days of deployment, chloroform, ethylbenzene, and toluene were detected by both passive sampling and grab sampling at the same VOC concentrations.

(Z)-1-Chloro-2,3,3,3-tetrafluoropropene (2017)

(Z)-1-Chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd(Z)) is a colorless gas used as a single substance or in a mixture with other substances for refrigeration. The 4-h rat inhalation LC₅₀ values from two studies were reported to be >20,180 ppm and >213,100 ppm. HCFO-1224yd(Z) is not expected to undergo significant metabolism. The no-observed-effect level of HCFO-1224yd(Z) for cardiac sensitization (in dogs) was 75,000 ppm. In a 5-day repeat inhalation study in rats, the only observation noted was repetitive movement of the mouth/jaws in some animals in the 50,000-ppm exposure group for 1-2 days during the first 3 exposure days. The toxicological significance of this observation was unknown; therefore, the study no-observed-adverse-effect level (NOAEL) was established at 50,000 ppm. In a good laboratory practice (GLP)-compliant, 4-week inhalation study in rats, there were no test substance-related adverse effects noted at any exposure concentration. The study NOAEL was established at 40,000 ppm. In a GLP-compliant inhalation developmental toxicity study, female rats were exposed for 6 h/day from gestation day 6 through 19. There were no test substance-related adverse effects on either the maternal or fetal rats at any exposure concentration. The NOAEL for developmental effects was established at 20,000 ppm. There are no chronic toxicity or carcinogenicity studies available. HCFO-1224yd(Z) gave mixed results in in vitro genotoxicity assays but was negative in an in vivo micronucleus assay. The NOAEL of 40,000 ppm for HCFO-1224yd(Z) from the 4-week, GLP-compliant inhalation study in rats was used at the point of departure (POD) for workplace environmental exposure level (WEEL) value development. This POD was adjusted to account for interindividual variability, duration of exposure, and database limitations. The resulting 8-h time-weighted average WEEL value of 1000 ppm is expected to provide a significant margin of safety against any potential adverse health effects in workers exposed to HCFO-1224yd(Z).

Trifluoroiodomethane (CF3I) (2019)

Trifluoroiodomethane (CF₃I) is a colorless and odorless gas used primarily as a fire suppressant. CF₃I has low acute inhalation toxicity. The no-observed adverse effect level (NOAEL) of CF₃I for cardiac sensitization in dogs was 2000 ppm. The potential effects of 4-week inhalation exposure in both rats and mice have been examined. In rats, the NOAEL was 10,000 ppm, and in mice, the NOAEL was 10,000 ppm. In a subchronic inhalation study in rats, the lowest observed adverse effect level (LOAEL) was 20,000 ppm for thyroid-related effects; the study NOAEL (for non-thyroid-related effects) was 20,000 ppm. In a reproductive/developmental inhalation toxicity study in rats, 20,000 ppm CF₃I produced minimal general toxicity and no indication of reproductive or developmental toxicity. The LOAEL for parental toxicity (based on thyroid hormone effects) was 2000 ppm; excluding thyroid effects, the parental NOAEL was 7000 ppm CF₃I. The observed effects on the thyroid in rats were considered of less relevance to human risk assessment than the other observed systemic effects because of known species-specific differences in sensitivity to thyroid hormone perturbations. There are no chronic toxicity or carcinogenicity studies available. CF₃I had mixed results in various in vitro and in vivo genotoxicity assays. The NOAEL of 7000 ppm from the reproductive/developmental inhalation study was used as the point of departure (POD) for workplace environmental exposure level (WEEL) value development. This POD was adjusted to account for interindividual variability, duration of exposure, and database limitations. The resulting 8-h time-weighted average WEEL value of 500 ppm is expected to provide a significant margin of safety against any potential adverse health effects in workers exposed to CF₃I. A 15-min short-term exposure limit of 1500 ppm was also established to protect workers from potential cardiac effects produced by acute, high-dose inhalation of CF₃I.

Trans-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz-E) (2018)

Trans-1,1,1,4,4,4-hexafluoro-2-butene (HFO-133mzz-E) is an odorless gas that finds uses as a foam transfer agent, heat transfer fluid, and specialty gas. The acute 4-h LC₅₀ (in rats) for HFO-133mzz-E is > 17,000 ppm; it was not an eye or dermal irritant in 3- and 13-week repeated-dose inhalation studies in rats at concentrations up to 1.5% (15,000 ppm). HFO-133mzz-E was not a cardiac sensitizer at 70,000 ppm in a standard epinephrine challenge study in Beagle dogs. In a 3-week, repeated-dose (non-GLP) inhalation range-finding study in male and female rats, HFO-133mzz-E concentrations of 7500 and 15,000 ppm were determined to be well-tolerated. In the follow-up, GLP-compliant, 28-day repeated-dose inhalation study (as per OECD 412), male and female rats were exposed to 0, 1000, 10,000, or 15,000/20,000 ppm (20,000 ppm concentration was decreased to 15,000 ppm after week 1 because of deaths and body weight loss). The study no-observed-adverse-effect level (NOAEL) was established at 10,000 ppm based on reduced body weight gain and mortality observed at 15,000 ppm. In a 90-day GLP-compliant repeated-dose study (as per OECD 413), male and female rats were exposed to 0, 1000, 5000, 7500, or 15,000 ppm HFO-133mzz-E. Three male rats exposed to 15,000 ppm HFO-133mzz-E died during exposure; clinical signs such as restlessness, blepharospasm, and myoclonic jerks were also observed, during the first month of the study, at 15,000 ppm. There were no significant gross or histopathological organ/tissue lesions attributable to HFO-133mzz-E exposure. The study NOAEL was established at 7500 ppm. In a GLP prenatal developmental study (OECD 414), groups of time-mated nulliparous female rats were exposed via inhalation to 0, 1000, 5000, 7500, or 15,000 ppm HFO-1336mzz-E beginning on gestation day (GD) 6 up to and including GD 19. Under the conditions of this study, the NOAEL for maternal and fetal effects was established at 7500 ppm. HFO-1336mzz-E was not genotoxic in either in vitro or in vivo assays. Based on the results of the 90-day inhalation study, 7500 ppm was determined to be the NOAEL and was selected as the point of departure for the derivation of the 8-h time-weighted average (TWA), health-based workplace environmental exposure level (WEEL) value. This subchronic inhalation NOAEL was adjusted to account for duration of exposure, interindividual variability, and intraindividual variability. The resulting 8-h TWA WEEL value of 400 ppm is fully expected to provide a significant margin of safety against the production of any potential adverse health effects in workers following long-term inhalation exposure to HFO-1336mzz-E.

1,1,1,3,3,3-Hexamethyldisilazane (2018)

1,1,1,3,3,3-Hexamethyldisilazane (HMDZ) is used industrially to treat the surface of silica, as an intermediate adhesion promoter or silylating agent in the semiconductor industry, as a chemical modifier of inorganic fillers, and as a water scavenger silicone sealant. In animal studies, HMDZ is considered to be slightly to at most moderately toxic following acute administration via oral, dermal, and inhalation routes of exposure. HMDZ is neither an eye irritant nor was it dermally irritating under semiocclusive conditions; however, it caused dermal necrosis in two studies under occlusive conditions. HDMZ is not genotoxic or mutagenic in in vitro assays and was not reproductively or developmentally toxic in an inhalation screening study in rats. Short-term and subacute, high-dose inhalation exposure to HMDZ produced respiratory tract irritation, reduced feed consumption, changes in clinical chemistry parameters, and reversible central nervous system depression in rats. In a 90-day inhalation exposure study in rats, HMDZ exposure-related effects were observed in the kidneys of male rats but were determined to be alpha-2µ-nephropathy, thus, not relevant to humans. Based on the results of the 90-day (subchronic) inhalation study, 75 ppm was determined to be the no-observed adverse effect level (NOAEL) and was selected as the point of departure for the derivation of the 8-h time-weighted average (TWA), health-based workplace environmental exposure level (WEEL) value. This subchronic inhalation NOAEL was adjusted to account for duration of exposure, interindividual variability, and intraindividual variability. The resulting 8-h TWA WEEL value of 10 ppm is fully expected to provide a significant margin of safety against any potential adverse health effects in workers following long-term inhalation exposure to HMDZ vapor. A 15-min short-term exposure limit of 50 ppm was also established to protect workers from reversible effects produced by acute, high-dose inhalation of HMDZ vapor. A skin notation (Skin) is warranted because of the potential for the dermal route to significantly contribute to the overall exposure to HMDZ.

Cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz-Z) (2018)

Cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz-Z) is a clear, colorless liquid that finds uses as a foam-blowing agent, refrigerant, fire extinguishing agent, and solvent. HFO-1336mzz-Z is not an acute dermal or eye irritant and has very low acute toxicity via inhalation exposure (4-h lethal concentration (LC₅₀) > 102,000 ppm). The no-observed adverse effect level (NOAEL) and lowest-observed adverse effect level (LOAEL) for cardiac sensitization (in epinephrine-challenged dogs) were 12,500 ppm and 25,000 ppm, respectively. In a GLP, subacute (4-week) repeat-dose inhalation study in Crl: CD(SD) male and female rats at exposure concentrations of 0, 2500, 5000, or 10,000 ppm, the only significant observations attributed to exposure were reduced body weight, reduced body weight gain, and reduced food consumption. The study NOAEL was determined to be 2500 ppm. Two separate GLP, 13-week repeat-dose inhalation studies (Organisation for Economic Cooperation and Development (OECD) 413) have been conducted on HFO-1336mzz-Z using male and female Crl: CD (SD) rats. In the first study, exposure concentrations were 0, 500, 1500, or 10,000 ppm, and in the second study, 0, 3000, 4000, 5000, or 7500 ppm. The only significant exposure-related observations in the first study were reductions in body weights, food consumption, and food efficiency in males and females at 10,000 ppm (study NOAEL = 1500 ppm). In the second study, done in part to better define the NOAEL, reductions in body weight and food consumption were observed in males at 7500 ppm; there were no exposure-related observations on these end points in females. Therefore, the study NOAEL was established at 5000 ppm for males and 7500 ppm for females. HFO-1336mzz-Z has also been examined for its potential to produce developmental toxicity in both Crl: CD(SD) rats (0, 500, 1500, or 10,000 ppm) and New Zealand White rabbits (0, 2500, 5000, 7500, or 15,000 ppm) according to GLP and OECD 414. The NOAEL for both maternal and fetal effects in rats was 1500 ppm and the NOAELs for maternal effects and fetal effects in rabbits were 5000 ppm and 7500 ppm, respectively. A non-GLP, two-generation reproductive pilot study, for a planned multigenerational study noted reduced body weight and body weight gain in males at 1500 ppm and above; the NOAEL for this pilot study was set at 500 ppm. There are no chronic toxicity/carcinogenicity studies available, and HFO-1336mzz-Z was not genotoxic/mutagenic in in vitro and in vivo studies. The NOAEL for male rats of 5000 ppm (based on reductions in body weight and food consumption) from the 13-week inhalation study was selected as the point of departure for the derivation of the 8-h time-weighted average (TWA), health-based workplace environmental exposure level (WEEL) value. This subchronic inhalation NOAEL was adjusted to account for duration of exposure, inter-individual variability, and intra-individual variability. The resulting 8-h TWA WEEL value of 500 ppm is fully expected to provide a significant margin of safety against the production of any potential adverse health effects in workers following long-term inhalation exposure to HFO-1336mzz-Z vapor.

Optimization of Time-Weighted Average Air Sampling by Solid-Phase Microextraction Fibers Using Finite Element Analysis Software

Determination of time-weighted average (TWA) concentrations of volatile organic compounds (VOCs) in air using solid-phase microextraction (SPME) is advantageous over other sampling techniques, but is often characterized by insufficient accuracies, particularly at longer sampling times. Experimental investigation of this issue and disclosing the origin of the problem is problematic and often not practically feasible due to high uncertainties. This research is aimed at developing the model of the TWA extraction process and optimization of TWA air sampling by SPME using finite element analysis software (COMSOL Multiphysics, Burlington, MA, USA). It was established that sampling by porous SPME coatings with high affinity to analytes is affected by slow diffusion of analytes inside the coating, an increase of their concentrations in the air near the fiber tip due to equilibration, and eventual lower sampling rate. The increase of a fiber retraction depth (Z) resulted in better recoveries. Sampling of studied VOCs using 23 ga Carboxen/polydimethylsiloxane (Car/PDMS) assembly at maximum possible Z (40 mm) was proven to provide more accurate results. Alternative sampling configuration based on 78.5 × 0.75 mm internal diameter SPME liner was proven to provide similar accuracy at improved detection limits. Its modification with the decreased internal diameter from the sampling side should provide even better recoveries. The results obtained can be used to develop a more accurate analytical method for determination of TWA concentrations of VOCs in air using SPME. The developed model can be used to simulate sampling of other environments (process gases, water) by retracted SPME fibers.

2,4-Dinitroanisole (DNAN) (2014)

2,4-dinitroanisole (DNAN) is a warhead explosive currently under investigation as a replacement for TNT in melt-cast insensitive munitions. In animal studies, DNAN is a mild ocular and skin irritant with a significant potential for dermal absorption.  It is not a dermal sensitizer.  Acute and subacute rat inhalation studies demonstrated minimal toxicity with LC₅₀ and LOAEL endpoints of 2.9 and 150 mg/m³, respectively.  In rat oral toxicity studies (14 and 90 days) organ weight and clinical chemistry changes suggested hepatocellular injury and anemia, particularly in females.  In males there was evidence of testicular injury at the high-dose level (80 mg/kg/day).  The NOAELs for the 14- and 90-day studies were 25 and 5 mg/kg/day, respectively, with a calculated BMDL₁₀ value of 0.93 mg/kg/day.  No chronic, carcinogenicity or reproductive/developmental toxicity data were available for DNAN, but a maternal and fetal NOAEL of 5.1 mg/kg/day was inferred.  DNAN is considered non-mutagenic and non-genotoxic.  It is metabolized in vivo to 2,4-dinitrophenol (DNP), but other details of its metabolism or pharmacokinetics are unknown.  There are considerable toxicity data for DNP, a known un-coupler of oxidative phosphorylation among other things, and these data may further inform regarding the safety of DNAN.  In humans, DNAN was a component of louse powder (prior to DDT) with no reported safety concerns.  However, its handling and use as a munition component presents a potential occupational hazard by both inhalation and dermal routes of exposure.  Considering both DNAN and DNP toxicity endpoints, the recommended Workplace Environmental Exposure limit for DNAN is 0.1 mg/m² (8-h time weighted average).

Nitroguanidine (NQ) (2016)

1-Nitroguanine (NG), also known as picrate, guanidine nitro, and N'-nitroguanidine, is used by the military as a propellant. Oral rodent LD₅₀ data are generally >5000 mg/kg. NG is neither an eye nor a skin irritant, and it is not a skin sensitizer. NG is not genotoxic. No inhalation data are available; however, there are data from both 14- and 90-day oral (feed) toxicity studies in male and female Sprague Dawley rats at dosages up to 1000 mg/kg/day. There were no deaths on these studies and the only effect considered possibly related to treatment was decreased weight in females at the high-dose level in the 90-day study. Mice at similar dosages were even less affected. The NOAEL for both rats and mice (oral) was 316 mg/kg/day. There was no evidence of developmental toxicity in Sprague-Dawley rats administered NG by oral gavage, and the free-standing NOAEL was 1000 mg/kg with material toxicity. In Wistar rats, there was high mortality (50%) at 500 mg/kg NG administered by oral gavage; there was decreased body weight, feed consumption, and notable clinical signs in the dams at this dose level. Fetal toxicity could not be determined in this group. NG demonstrated maternal toxicity at 1000 mg/kg in rabbits; however, there were no evident differences in the rate of fetal malformations across the test groups. A NOAEL of 316 mg/kg was identified for maternal and fetal toxicity in this study. In a two-generation study, it was concluded the NG did not cause reproductive or fertility effects at dosages up to 1000 mg/kg/day. Absorption was rapid, non-dose dependent, and resulted in an apparent volume of distribution (V_D) of between 0.66 (IV) and 0.85-0.87 (oral) l/kg. Elimination was primarily through the urine as unchanged compound. Human experience with NG dates back 100 years; however, no actual studies on humans have been reported. Non-military uses include automotive airbags, anti-corrosive coatings, and pharmaceutical manufacturing. The point of departure for Workplace Environmental Exposure Level (WEEL) derivations was 316 mg/kg, and a WEEL of 7 mg/m³ as an 8-h time-weighted average (TWA) was recommended.

Octamethylcyclotetrasiloxane (D4)

Octamethylcyclotetrasiloxane (D4; CAS No. 556-67-2) is used as a monomer in the manufacture of polymeric materials, which are widely used in various industrial and/or medical applications, such as breast implants. D4 has a relatively low order of toxicity following acute administration via the oral, dermal, and inhalation routes of exposure and is not considered to be a dermal or eye irritant or to be a dermal sensitizer. There is no appreciable dermal absorption of D4 based on results from in vivo and in vitro studies. D4 has not been shown to be genotoxic/mutagenic when tested in a number of short-term in vitro and in vivo assays. Overall, studies have demonstrated adverse effects on specific female reproductive endpoints at higher exposure concentrations; however, no D4 exposure-specific effects were noted with respect to developmental endpoints. Inhalation exposure of rats to 700 ppm D4 for up to 24 months produced effects in the liver, kidney, and uterus (weight changes, hepatocellular hypertrophy, endometrial hyperplasia, and nephropathy). Changes in the nasal epithelium (eosinophilic globules) were also noted at 150 and 700 ppm. Despite 24 months of exposure, only mild to minimal inflammatory responses were found at 150 ppm, and overall, the basic integrity of the respiratory tract was unchanged at this dose. At 700 ppm, there was an increased incidence of endometrial adenomas in female rats. Based on the adverse changes in the respiratory tract, kidney, and female reproductive tract in the chronic inhalation study, 150 ppm was determined to be the no-observed-adverse-effect level (NOAEL) and was selected as the point of departure for the derivation of the workplace environmental exposure level (WEEL®) value. The inhalation NOAEL was adjusted to account for interindividual variability and residual uncertainty regarding upper respiratory tract changes still occurring at 150 ppm. An 8-h time-weighted average WEEL value of 10 ppm is expected to provide a significant margin of safety against any potential adverse health effects in workers exposed to airborne D4.

Decamethylcyclopentasiloxane (D5)

Decamethylcyclopentasiloxane (D5; CAS No. 541-02-6) is a precursor in the production of siloxane polymers for industry and medicine and is a carrier ingredient in many toiletries and cosmetics. D5 has a relatively low order of toxicity following acute administration via the oral, dermal, and inhalation routes of exposure. It is not considered to be a dermal or eye irritant or a dermal sensitizer. There is no appreciable dermal absorption of D5 based on results from in vivo and in vitro studies. It has not been shown to be genotoxic/mutagenic when tested in a number of short-term in vitro and in vivo assays and did not cause reproductive or developmental toxicity in rats. Inhalation exposure of rats to 160 ppm D5 for up to 24 months produced adverse effects in the liver (weight changes and hepatocellular hypertrophy) and uterus (increased incidence of endometrial adenocarcinoma, endometrial adenoma, and adenomatous polyps in several animals); however, the results of recent mode-of-action studies are consistent with a uterine tumorigenesis mechanism that is not relevant for humans. Based on the results of the chronic inhalation study, 160 ppm was determined to be the no-observed-adverse-effect level (NOAEL) and was selected as the point of departure for the derivation of the workplace environmental exposure level (WEEL®) value. This NOAEL was adjusted to account for interindividual variability and residual uncertainty regarding upper respiratory tract changes still occurring at 160 ppm. The resulting 8-h time-weighted average WEEL value of 10 ppm is expected to provide a significant margin of safety against any potential adverse health effects in workers exposed to airborne D5.

The Cumulative Lifting Index (CULI) for the Revised NIOSH Lifting Equation: Quantifying Risk for Workers With Job Rotation

OBJECTIVE

The objectives were to: (a) develop a continuous frequency multiplier (FM) for the Revised NIOSH Lifting Equation (RNLE) as a function of lifting frequency and duration of a lifting task, and (b) describe the Cumulative Lifting Index (CULI), a methodology for estimating physical exposure to workers with job rotation.

BACKGROUND

The existing FM for the RNLE (FME) does not differentiate between task duration >2 hr and <8 hr, which makes quantifying physical exposure to workers with job rotation difficult and presents challenges to job designers.

METHOD

Using the existing FMs for 1, 2, and 8 hr of task durations, we developed a continuous FM (FMP) that extends to 12 hr per day. We simulated 157,500 jobs consisting of two tasks each and, using different combinations of Frequency Independent Lifting Index, lifting frequency and duration of lifting. Biomechanical stresses were estimated using the CULI, time-weighted average (TWA), and peak exposure.

RESULTS

The median difference between FME and FMP was ±1% (range: 0%-15%). Compared to CULI, TWA underestimated risk of low-back pain (LBP) for 18% to 30% of jobs, and peak exposure for an assumed 8-hr work shift overestimated risk of LBP for 20% to 25% of jobs. Peak task exposure showed 90% agreement with CULI but ignored one of two tasks.

CONCLUSION

The CULI partially addressed the underestimation of physical exposure using the TWA approach and overestimation of exposure using the peak-exposure approach.

APPLICATION

The proposed FM and CULI may provide more accurate physical exposure estimates, and therefore estimated risk of LBP, for workers with job rotation.