As a safety professional, you are required to protect your employees from hazardous chemicals on the job. You know one essential item of personal protection equipment (PPE) for working with chemicals is a pair of chemical-resistant gloves. You specify the gloves for each employee based on the chemicals present and the type of exposure they may encounter, and you use manufacturers' test results to determine which gloves are correct.
You are diligent about doing your homework, so as long as the employees wear the specified glove, they are protected, correct? Maybe not.
Temperature can have a significant effect on the chemical-resistant properties of some materials used to manufacture gloves. And the glove specifications, developed from sophisticated tests, may not accurately indicate how the glove will perform in actual use. This article will shed some light on the impact of heat from various sources on the chemical-resistant properties of different glove materials.
The primary protocol for testing chemical-resistant materials, and the gloves that are made from these materials, was developed and published by the American Society for Testing and Materials International (ASTM). Much of the experimental work conducted in the development of ASTM Standard F 739 Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids or Gases Under Conditions of Continuous Contact involved studies of temperature and its effect on permeation. Results from this testing indicate that temperature directly affects the permeation of chemicals through chemical-protective clothing. Increasing the temperature causes chemicals to break through sooner and to reach a constant steady rate of permeation. Since permeation is diffusion, it is obvious that higher temperatures cause faster diffusion and lower temperatures cause slower diffusion.
Slight Difference Equals Big Change
Even slight differences in the temperature can cause dramatic differences in the chemical-resistance behavior of polymeric materials used in glove construction. For instance, when benzene was tested on neoprene gloves at several temperatures, the breakthrough time was reduced by 33 percent by raising the temperature from room temperature to body temperature. The breakthrough time was reduced from 24 minutes to 16 minutes, and the permeation rate increased.
Chemical resistance data reported by chemical protective clothing manufacturers follows the criteria set forth by ASTM. The test method mentioned above calls for testing of protective clothing at room temperature, which is generally thought of as a temperature of 21 + 5 degrees C (70 + 9 degrees F). All chemical resistance data is based on room temperature, not elevated temperatures such as body temperature. The testing data found at manufacturer's Web sites is derived from tests conducted at room temperature, and may be unreliable at higher temperatures.
Fluctuations in the temperature from weather changes can also have a marked effect on the longevity of chemical-protective clothing. In the winter, PPE may last much longer than in the heat of summer. Some chemicals that are reported as "none detected" with breakthrough times greater than eight hours may actually break through chemical-protective clothing when the temperature is slightly elevated.
There is no rule-of-thumb. For some chemicals, there is no difference in the breakthrough time of permeation rate when exposed to body heat or warm weather, but others can be markedly influenced. It is important to remember ASTM chemical-resistance testing is designed to mimic the worst-case or maximum exposure scenario with total constant immersion in the test chemical. However, it is still a laboratory test and therefore limited in some regards. In addition to fluctuations in the temperature brought about by the causes mentioned above, differences brought on by other factors such as wear or friction can also affect the permeation characteristics.
Danger of Heated Chemicals
Another important factor to consider when choosing the correct chemical-resistant glove is the temperature of the chemicals being handled. Hot chemicals pose additional hazards for at least two reasons: increased permeation of the chemical through the glove, and the impact of a heated liquid on the skin itself. For instance, heated sulfuric acid can cause much more severe burns than unheated sulfuric acid.
If the skin is burned at temperatures lower than 75 degrees C (167 degrees F), the skin retains its essential barrier properties until the damaged skin is sloughed. But if skin receives a burn at temperatures of 85 degrees C (185 degrees F) or higher, the permeability of the skin is immediately altered and the damage is irreversible.
The danger of heated chemicals cannot be over-emphasized. With a thermal burn, the instantaneous permeation of the chemical into the bloodstream and the resulting toxic effect on target organs or body systems can result in a life-threatening injury. Anyone subject to exposure to chemicals at temperatures above 85 degrees C (185 degrees F) should be made aware of the additional risks contact with the chemicals carry.
If the chemical is heated, you must take this factor into consideration when choosing the correct chemical-resistant gloves. Although the chemical resistance data is a good rule of thumb, permeation and breakthrough data should be considered best-case values since heated chemicals can degrade the behavior of the glove's polymer and the safety performance of the products that are being trusted to protect workers.
Solutions
Are there any gloves designed for high temperatures and chemicals? The answer is yes, and no. There are insulated neoprene and nitrile gloves that contain foam-insulating components in the fabric liners. But there is really nothing that can be done to the polymer coatings themselves to make them more chemical-resistant. The insulated linings provide some degree of protection from the thermal heat, but an insulated lining does not provide any more chemical protection than an unlined glove.
Skin Absorption
Chemicals that are toxic exhibit their effects in a variety of ways. They can cause damage locally, with tissue destruction or damage to the stratum corneum or the epidermis. Massive tissue death and scarring can result from exposure to acids or caustics, and the damage can occur much quicker if the chemical is heated.
Chemicals can also be absorbed through intact skin and cause a systemic or target organ toxic effect. For example, ethanol targets the brain or liver, benzene targets the liver, methanol targets the eye, acetaminophen targets the liver, and Paraquat targets the lungs. The American Conference of Governmental Industrial Hygienists designates a chemical with a "skin notation" if the chemical can be absorbed into intact skin.
Absorption through intact skin is also a diffusion phenomenon, which can be directly affected by temperature in the same way as permeation is affected. The higher the temperature inside the glove, the faster the rate of absorption by the skin. This produces a cumulative effect, the heated chemical permeates the glove more quickly than the specifications indicate, and the skin absorbs the chemical faster than normal.
Another major factor in determining the amount of chemical that is absorbed through intact skin is occlusion (sealing off). In humans, absorption of a topical dose of hydrocortisone increased from 0.5 percent of the applied dose to 4.5 percent after occlusion of the dose site. Absorption of cinnamic acid through monkey skin rose from 38.6 percent to 83.9 percent when the dermal surface was occluded. In rabbits used for dermal toxicity testing, one study showed that 1.0 g/kg of hydroxylamine sulfate was not lethal to animals when the treated skin was covered with only gauze dressing. However, occlusion with plastic resulted in death of 90 percent of rabbits receiving only half this dose. Wearing a glove is, in effect, occluding the entire hand.
Occlusion can increase the toxic effects of a chemical by increasing the dose or amount of chemical that is absorbed. This happens because:
- Hydration of the skin is increased.
- The temperature of the skin is increased.
- The substance remains in contact with the skin for a longer period of time.
- The evaporation of volatile materials is prohibited.
In summary, we must always take into consideration the heat that may be involved when working with chemicals. Higher temperatures from body heat, weather or heated chemicals can mean injury from chemical exposure is much more likely. Gloves should be changed much more often in hot conditions. If a chemical does permeate through a glove, it can cause more damage because of occlusion and increased absorption of the chemical through skin. Finally, it would be beneficial if manufacturers that performed their own testing would test gloves at higher temperatures and publish those results along with results from the ASTM Standard F739 methodology.
About the author: Donald F. Groce, Best Manufacturing, is a technical product specialist and a research chemist. Before joining Best, he worked for the U.S. Centers for Disease Control and Prevention on chemical toxicology studies, including the Agent Orange study. He is a noted speaker and expert on a variety of occupational and workplace hazards, including latex allergies and chemical exposure-related illnesses. Best Manufacturing provides several lines of chemical-resistant gloves, made from a wide variety of polymers. Best maintains the www.chemrest.com Web site, one of the most extensive repositories of testing data on chemical-resistant gloves.