The gloves were disposable, powder-free exam gloves with a reported length of 24 cm and palm thickness of 0.10-0.13 mm (4-5 mil). The brands tested (Table I) were Fisherbrand Latex, Safety Choice Nitrile, and Safety Choice Vinyl gloves (Fisher Scientific, Pittsburgh, PA, USA). Latex, nitrile and vinyl gloves were chosen for comparison because they are common and available glove choices, inexpensive, and their material compatibility charts from a glove supplier (http://www.coleparmer.com/Chemical-Resistance) indicated that protection would be likely against ethyl alcohol. Preliminary degradation testing indicated no significant weight or thickness change (p ≤ 0.05) or observable signs of material degradation with the three glove materials following a 2 hour exposure to ethyl alcohol. Chemical permeation was conducted using 200 mL ethyl alcohol, denatured (Fisher Scientific, Pittsburgh, PA, USA) as a representative test chemical.

A previously designed test system was used to expose gloves to simulated whole-glove movement and measure permeation parameters.^{(2, 12)} Closed-loop permeation monitoring for ethyl alcohol was conducted within a permeation chamber using a datalogging Minirae 2000 photoionization detector (PID) (Rae Systems, San Jose, CA, USA). Chamber concentrations were averaged and recorded every 30 seconds by the PID. The permeation chamber was a 29.2 cm × 25.4 cm × 30.5 cm stainless steel and glass Boekel 1340 environmental chamber (Fisher Scientific, Pittsburgh, PA, USA). The PID was calibrated at the beginning of the day and checked at the end of each run. The PID was recalibrated if readings exceeded ± 3% of the 100 ppm isobutylene calibration check standard. Permeation runs were invalidated if the calibration check exceeded ± 5%. All PID readings were corrected using a measured response factor for ethyl alcohol, based on a standard curve from known concentrations of ethyl alcohol in Tedlar® bags.

The permeation parameters were determined using Microsoft Excel, to evaluate test chamber concentrations and changes in concentration over time. The BT was determined as the first increase of 0.4 μg/cm², where all subsequent measures continued to increase. The rationale for this determination is provided in a previous study.⁽²⁾ The SSPR was calculated using at least ten data points within the linear region of the permeation curve. A third measure, cumulative permeation (in units of μg/cm²) at 30 minutes (CP₃₀), was determined to aid in the comparison of permeation results with studies incorporating standardized measures in accordance with American Society for Testing and Materials (ASTM) Method F739 Standard Test Method for Resistance of Protective Clothing Materials to Permeation of Liquids or Gases under Conditions of Continuous Contact.⁽¹³⁾

For simulated whole-glove movement, inflation and deflation of the glove was controlled using a GeoControl Pro pneumatic controller (Geotech Environmental Equipment, Inc., Denver, CO, USA) and magnehelic pressure gauge (Dwyer Industries, Inc., Michigan City, IN, USA). The inflation pressure was controlled to within a gauge pressure reading of 0.10 ± 0.02 inches of water. The inflation and deflation cycle time was 30 seconds, in which the gloves were in continual movement more than 80% of the time. As in a previous study,⁽¹²⁾ all permeation tests were performed within a fume hood and a Pelican 1500 case (Pelican Products, Torrance, CA, USA) with an installed 5 liter Tedlar® bag was used as an intermediate chamber to separate and protect the pneumatic pump from ethyl alcohol vapors, as previously described.

The no movement and movement runs were matched and paired to control for variations in room temperature (21.4 ± 1.0 °C) and relative humidity (35 ± 15%). Ambient conditions were used for safety and health reasons.

Sample sizes (Table I), ranging from 20 to 26 per test condition (no movement or movement), were adjusted to detect a 10 percent change in permeation parameters upon exposure to movement, using a t-test. The total sample sizes ranged from 40 to 52 per glove. Statistical analyses were performed using IBM SPSS Statistics 19 (IBM, Armonk, NY, USA). Histograms, and skewness and kurtosis normality tests indicated that the permeation results were near normally distributed. Because the no movement and movement tests were matched and paired, to account for variations in ambient conditions, paired t-tests were used. Results were considered significant if the p value was ≤ 0.05.

The BT data are illustrated in Fig. 1, which shows the average BT data for no movement and movement exposures, plus a statistical comparison of the percent change for each glove product. With exposure to movement, a significant decrease (p ≤ 0.001) in BT was observed for the latex and nitrile gloves. The decrease in BT ranged from 23 to 31 %, respectively. No significant change in BT (p = 0.12) was observed with the vinyl glove.

Significant variation in BT existed between the glove types. Without movement, the average BT for the nitrile glove was about 3.5 times longer than the latex glove and 10 times longer than the vinyl glove. This effect was similar with the addition of movement; the average BT for the nitrile glove was about 4 times longer than the latex glove and about 14 times longer than the vinyl glove. The differences were slightly larger with the addition of movement.

The SSPR data are illustrated in Fig. 2, which shows the average SSPR data for no movement and movement exposures, plus a statistical comparison of the percent change for each glove product. With exposure to movement, a significant increase (p ≤ 0.001) in SSPR was observed only for the nitrile glove, with a 47 percent increase, on average. No significant change in SSPR (all p > 0.2) was observed with the latex or vinyl gloves.

Without movement, the average SSPR varied slightly between the glove materials, with percent differences ranging from 12 to 40 percent. However, the effect was more pronounced with exposure to movement, with percent differences ranging from 26 to 70 percent. The primary cause of this increase in effect was with the significant increase in SSPR with the nitrile glove when exposed to movement.

The cumulative permeation data are illustrated in Fig. 3, which shows the average CP₃₀ data for no movement and movement exposures, plus a statistical comparison of the percent change for each glove product. With exposure to movement, a significant increase (p ≤ 0.001) of 111 percent, on average, in CP₃₀ was observed only for the nitrile glove. No significant change in CP₃₀ (all p > 0.05) was observed with the latex or vinyl gloves.

Without movement, the average CP₃₀ values varied significantly between the glove materials, with percent differences ranging from 85 to 270 percent. However, the effect was less pronounced with exposure to movement, with percent differences ranging from 10 to 100 percent. The primary cause of this decrease in effect was with the significant increase in CP₃₀ with the nitrile glove when exposed to movement.

The results shown in Fig. 1, Fig. 2 and Fig. 3 indicated that simulated movement had a significant effect on chemical permeation with the nitrile glove, but not the latex or vinyl gloves. On average, for the nitrile glove, movement resulted in a decrease in BT of about 24%, an increase in SSPR of about 47%, and an overall increase in CP₃₀ of 111%. With the nitrile glove, permeation occurred both sooner and at a faster rate with movement. These results are consistent with a similar study evaluating the effect of movement on the permeation of ethyl alcohol through disposable nitrile gloves.⁽²⁾ Phalen and Wong reported comparable results with up to a 33% decrease in BT and up to a 78% increase in SSPR with exposure to simulated whole-glove movement.⁽²⁾ A 3-fold increase in cumulative exposure, as the area under the permeation curve at 30 min (AUC₃₀), was also reported, which does not directly compare with the 1-fold increase in CP₃₀ in this current study. It has been shown that area under the permeation curve can provide an improved estimate of worker exposure over time;⁽²⁾ however, both AUC₃₀ and CP₃₀ are a function of the BT and SSPR. The estimated AUC₃₀ for the nitrile glove exposed to no movement can be estimated using the formula:⁽²⁾

The equivalent calculation for the AUC₃₀ with exposure to movement (BT = 7.8 min and CP₃₀ = 211 μg/cm²) is about 2,340 min·μg/cm². This equates to about a 2.5-fold increase in estimated AUC₃₀, which is consistent with the previously reported up to 3-fold increase.⁽²⁾ Therefore, for the purpose of assigning a workplace protection factor, at least a 3-fold increase in worker exposure should be assumed with repetitive hand movements over a 30 min period.

The results for the latex glove are not consistent with a previous study evaluating the effect of movement on permeation parameters. Colligan and Horstman studied the permeation of cyclophosphamide through a similar latex exam glove with a reported thickness of 0.16 mm.⁽³⁾ They found no significant change in normalized BT following exposure to flexure. However, the sample sizes were small at n = 3 to n = 4 and the standard deviations were high, with a calculated coefficient of variation ranging from 82 to 83 percent. In contrast, a significant increase in SSPR of about 50% was reported with exposure to flexure. These results are opposite the findings with ethyl alcohol permeation and simulated whole-glove movement. Colligan and Horstman used a modified Franz cell, which evaluates permeation for a small swatch of material.⁽³⁾ The amount of glove material flexure was not reported. Only a small volume of air, 7.5 cc, was displaced in the manifold system, but the number of test cells and pressure and vacuum measures were not reported, all which made it difficult to compare the two studies. The likely reasons for the differences include:

cyclophosphamide is a non-volatile compound and requires aqueous challenge and collection solvents to complete permeation testing, which can affect BT and SSPR determinations; ⁽¹⁴⁾

Further testing and evaluation of the effects of movement on permeation of latex gloves by volatile and not-volatile chemicals is needed.

For the vinyl glove, the results and conclusions matched well with those of Colligan and Horstman, who found no significant change in normalized BT or SSPR with cyclophosphamide permeation following exposure to flexure for a vinyl glove with a reported thickness of 0.12 mm.⁽³⁾ The general understanding that vinyl gloves provide good resistance to water and aqueous solutions,⁽¹⁷⁾ due in part to the high plasticizer content,⁽¹⁸⁾ also supports the prior reasoning on how the aqueous challenge and collection solvents may have affected the latex permeation results. In contrast, Perkins and Rainey also evaluated the effect of whole-glove movement on permeation of heptane through thicker 0.51 mm (20 mil) vinyl gloves, but found a decrease in BT and increase in SSPR associated with glove flexure.⁽¹⁾ The primary issue with this study was that vinyl gloves are generally not recommended for protection against heptane, or aliphatic/alicyclic hydrocarbons, due to poor resistance and potential degradation effects.^{(17, 19)} The general conclusion here is that permeation of vinyl gloves is less affected by movement, than the nitrile gloves.

Even though the nitrile gloves were affected more by movement than the other two polymer types, they did provide a significantly longer BT, regardless of movement. Without exposure to movement, the nitrile gloves performed well and had the longest BT (3.7-fold to 9-fold longer), an equivalent SSPR, and the lowest overall cumulative permeation (i.e., CP₃₀ 2-fold to 4-fold lower). Without exposure to movement, the nitrile glove was an optimal choice for protection against ethyl alcohol. With exposure to movement, the nitrile glove was still an acceptable choice.

With exposure to movement the latex glove was an equivalent option, as it was less affected by movement than the nitrile glove. There was no significant difference (p = 0.24) in CP₃₀ between the latex and nitrile gloves. For exposures beyond 30 minutes the latex glove is expected to outperform the nitrile glove, especially when repetitive hand movements are present. This is likely due to the reported differences in stiffness and immediate unrecovered stretch between similar disposable latex and nitrile gloves.⁽⁵⁾ A previous study evaluating the biomechanical properties of similar disposable latex and nitrile gloves indicated that latex gloves were less stiff and had improved recovery properties following stretching.⁽⁵⁾

Although, the vinyl glove was not affected by movement, it had the lowest BT, a high to moderate SSPR, and the highest CP₃₀, regardless of movement. The likely reason for this is the high plasticizer content, often up to 50%, with vinyl polymers.⁽¹⁸⁾ The high plasticizer content may help modify the plastic vinyl polymer into a more elastic product;⁽¹⁷⁾ however, organic solvents are more likely to interact with the phthalate or often oily plasticizers used with vinyl products.⁽¹⁸⁾

A major limitation of this study was that only one test chemical was evaluated, which limits the application to different chemical classes with these gloves materials. The findings may be relevant to similar aliphatic hydroxyl compounds, but they may not necessarily apply to different chemical classifications. As discussed earlier, ethyl alcohol was selected because it is known to permeate all three glove products rapidly without significant degradation. Furthermore, the American Conference of Governmental Industrial Hygienists Threshold Limit Value (TLV^®) is higher than most other alternatives, which adds a margin of health protection during testing.⁽²⁰⁾ It would have been ideal to tightly control temperature and relative humidity; however, the matched-pairs study design has been shown to provide reliable results.⁽¹²⁾ Use of a heating element with a flammable solvent posed an additional safety and health concern. Lastly, this study only evaluated three disposable glove products for protection against a chemical under light-use conditions (e.g., hospital and dental settings), where thicker chemically-protective gloves are not practical. The decision to use disposable gloves is a critical professional judgment for those practicing industrial hygiene.