Validation Testing of a Solvent Breakthrough Indicator for Use with Chemical Protective Gloves

Thomas D. Klingner, Colormetric Laboratories, Inc., Des Plaines, IL, USA (Corresponding Author)

Introduction
• The ACGIH lists over 170 chemicals with the potential to contribute to systemic toxicity and marks them with a Skin Notation (SK). This SK is inconsistent and ignores corrosives, sensitizers and irritants.

• Over 13 million workers in the United States are exposed to systemic toxins, yet, few data exist on the protection actually afforded by gloves.

• Dermatitis remains the primary occupational illness.

The selection of gloves and chemical protective clothing (CPC) is most often based on laboratory generated permeation data. ASTM laboratory tests are a good “starting point” in the glove selection process but actual field conditions may alter the glove’s performance and compromise worker safety. As discussed in a recent paper (Klingner and Boeniger, 2002), it is necessary to test the performance of gloves under actual use conditions to ensure worker safety.

Passive dermal dosimeters allow personal protective equipment (PPE) to be evaluated during “in use” or field conditions. Dermal dosimeters that are actually colorimetric sensors called Permea-Tec® sensors have been developed for highly toxic or sensitizing chemicals such as isocyanates, aromatic amines, acids or caustics. These sensors indicate breakthrough, i.e. end of service life, thereby greatly improving the glove selection process.

Most gloves are worn to protect against exposure to organic solvents or solvent mixtures. A visual indicator for solvent detection has been developed to detect permeation of polar solvents. The detection is based on microencapulating a colored dye. The capsule is sensitive to dissolution when exposed to solvents. By using a charcoal sorbent, this solvent sensor allows for quantification of total breakthrough dose.

It is important that an indicator of glove failure be correlated to the toxicological risk associated with the dermal exposure. For chemical solvents noted with SK, systemic toxicity is the concern. Sole reliance on laboratory generated breakthrough times (BTT) may allow significant exposure due to field use conditions that damage the glove’s protective qualities. In a second paper (Boeniger and Klingner, 2002), a target level of toxicological risk was proposed based on a percentage of the 8 hour occupational exposure limit (OEL) inhalation dose.

Klingner and Boeniger (2002) suggest a general approach for evaluating the acceptability of chemical protective gloves under “field use” conditions. A biologically relevant skin absorbed dose is established at 25% of the equivalent 8 hour inhalation dose at the OEL. The presumption is that it is unrealistic to require gloves to protect against all exposures when convention allows a “safe” inhalation exposure. A similar approach is useful in judging whether a colorimetric indicator of glove permeation is too sensitive or not sensitive enough.

By measuring the actual permeating exposure dose and comparing it to an estimate of the maximum acceptable systemic dose, the combined influence of breakthrough time (BBT) permeation rate (PR) and systemic toxicity are taken into account in the glove selection process.

The objective of this study was to compare the response of the solvent indicator to the target risk level for selected solvents.

Calculation of Skin Absorbed Dose
Conc = measured concentration (permeated mass per area) per glove use (mg/cm²)
SA = surface area (nominally 410 cm² for the fingers and palms of two hands, 840 cm² for two whole hands)
SAF = skin absorption factor, assumed to be 0.5 unless otherwise empirically known.
Thus, skin dose = number of gloves worn X Conc X SA X SAF
Inhalation dose (at the action level) = 10 m³ X 0.5 X OEL (mg/m³)

The relative skin absorbed dose, RSAD, is the ratio of the skin dose to the inhalation dose expressed as a percent.

RSAD =               Skin dose                 x 100%    
0.5 x inhalation OEL dose

RSAD less than 50% may be considered an acceptable skin dose.

Examples for estimating duration of acceptable use:

Compound 1:
Methyl alcohol, OEL = 200 ppm = 260 mg/m³
Inhalation dose (action level) = 10 m³ x 260 mg/m³ x 0.5 OEL = 1300 mg
Allowable glove dose = 0.5 OEL (action level) = 650 mg

Assuming the default SAF and exposure of two immersed hands, it would be most informative if the color change occurred when the amount of solvent that permeated the gloves is approximately

650 mg/840 cm² = 0.77 mg/cm².

Assuming only the fingers and palm of one hand were being exposed, the amount of solvent causing the color change should be approximately

650 mg/205 cm² = 3.2 mg/cm².

Compound 2:
Methyl hydrazine, OEL 0.2 ppm = 0.35 mg/m³
Inhalation dose (action level) = 10 m³ x 0.35 mg/m³ x 0.5 OEL = 1.75 mg
Allowable glove dose – 0.5 OEL (action level) = 0.84 mg

Assuming the default SAF and exposure of two immersed hands, it would be most informative if the color change occurred when the amount of solvent that permeated the gloves is approximately

0.84 mg/840 cm² = 0.001 mg/cm².

Assuming only the fingers and palm of one hand were being exposed, the amount of solvent causing the color change should be approximately

0.84 mg/205 cm² = 0.004 mg/cm².

Preliminary Evaluation of a Micro-Encapsulation Solvent Permeation Sensor 
Experimental Approach:
• Select a range of polar and non-polar solvents.
• Select various glove polymers to provide a range of BTTs and Steady State Permeation Rates.
• Perform “conventional” ASTM tests to characterize permeation action.
• Repeat tests with colorimetiric solvent indicator.
• Compare permeation data for both methods to calculated dermal exposure dose.

Note: PR - permeation rate, NR - natural rubber, PVA - polyvinyl alcohol, DMF - Dimethyl formamide, THF - Tetrahydrofuran

 

Table 3. Preliminary Solvent Permea-Tec® Sensor Data
OSHA PEL	Chemical	BTT ASTM	BTT Color	Measured Mass on Sensor	Target Mass on Sensor
None	Diethylene glycol dimethyl ether	24 min.	42 min.	0.077 mg	—
10 PPM 30 mg/M3	Dimethyl formamide	69 min.	105 min.	0.070 mg	0.75 mg
None	Gasoline	165 min.	ND >480 min.	>25 mg	—
200 PPM 260 mg/M3	Methyl alcohol	77 min.	152 min.	4.51 mg	6.5 mg
25 PPM 80 mg/M3	Methyl Cellosolve	40 min.	450 min.	5.3 mg	2.0 mg
200 PPM 590 mg/M3	Tetrahydro- furan	4 min.	4 min.	0.060 mg	14.7 mg
100 PPM 551 mg/M3	Trichloro- ethylene	19 min.	ND >240 min.	—	13.5 mg
200 PPM 750 mg/M3	Toluene	16 min.	23 min.	Est. 13.5 mg	18.75 mg

Table 3 represents the results from eight different chemical glove challenges. BTT ASTM is the BTT measured with the standard ATSM F-739 test protocol. BTT Color represents the exposure period to produce a positive color indication. ND indicates that no color change was detected during the experiment. The Measured Mass on Sensor column lists the cumulative mass of the permeated chemical that produced the color change, i.e., the chemical exposure detected by the indicator. The Target Mass on Sensor column lists the preferred mass of chemical that would cause a color change, which would be the mass reaching the 4.1 cm² sensor if 25% of the inhalation dose at the OEL were to permeate the fingers and palms of the gloves on two hands (410 cm²).

While it is interesting to note the relative breakthrough times measured by the two methods, the main comparison of interest is between the measured and target masses on the sensor when the color changes. Of the seven chemicals, two do not have a PEL, so no target was calculated. Of the remaining five chemicals, there is no measurement of the mass on the sensor for tricholoroethylene and the measurement for toluene is only an estimate. The sensor appears to be much too sensitive for tetrahydrofuran. It is too sensitive for dimethly formamide and approximately on target for methyl alcohol. It is somewhat less sensitive than desired for methyl cellosolve. It did not change color at all during the experiments with gasoline and trichloroethylene. The estimate indicates that it may be nearly on target for toluene.

Discussion
The primary purpose for incorporating the color indicator for solvents is to provide a visual warning of breakthrough for small industry. The majority of the workforce in the U.S. is employed by small companies of 50 workers or less. It is unlikely that these companies will readily employ laboratory analysis for the charcoal pad without a visual indication of exposure.

It is important that there is some correlation of the indicator response to a biologically significant exposure. Due to the wide range of solvent polarities and toxicities, it is impossible for a single indicator system to accomplish this and primary reliance should remain on laboratory analysis of the pad.

For those polar solvents tested, DMF, methanol, methylcellosolve and glycol ethers, the indicator responded to the chemical. In the cases of DMF, methanol and methyl cellosolve, the response is in the range that might make it quite useful for indicating that a health-significant amount of chemical has reached the sensor. For non-polar compounds, gasoline, trichloroethylene and perhaps, toluene, the current indicator was poorly responsive.

Potential for Future Development - As the use of passive dermal dosimetry for glove performance evaluation increases, it should be possible to improve and extend the range of response of the micro-encapsulation detection system. By employing an encapsulation polymer that is sensitive to non-polar solvents, detection of almost any solvent combination should be possible. Theoretically, it should also be possible to control the sensitivity of the indicator by varying the thickness and particle size of the microencapsulated indicator.