Module 4: Gloves - Glove Failure

Glove failure:

Having identified the hazards with an appropriate risk assessment and selected the best glove for the identified hazards, gloves still fail to protect the worker. The reason they fail is that the worker is uninformed of the limitations of glove usage. So what are the reasons for this failure? They fail because:

• they are abused;
• they suffer mechanical damage;
• they degrade;
• chemicals may easily permeate the glove material.

Each of these aspects of glove failure will now be discussed in detail.

Glove abuse:

Gloves are abused because they are inadequately chosen for the task needed. While most people will accept that one has to have a range of shoe sizes for safety boots, very often a single size of glove is all that is available in the work place. Ill-fitting gloves are a work hazard as they are easily torn and damaged and often abused to provide the worker with the dexterity necessary for the task. The cartoon on the left illustrates the sort of abuse that might be encountered where tactile sensation or fine movement control is being interfered with by the gloves: a worker cuts off the fingertip of the glove to permit the fine motor control necessary during the task to maintain line production time constraints.

Mechanical damage:

Mechanical damage on the other hand occurs from the routine wear and tear of gloves during the task for which they are supplied. If the task involves exposure to sharp objects, gloves are especially vulnerable. Routine wear and tear weakens the glove structure predisposing it to further mechanical damage.

With ill fitting gloves that are either stretched beyond their limit or are too big and therefore catch on machinery and objects, mechanical damage is easy. Mechanical damage is much more likely to occur in combination with degradation of glove material.

Degradation:

Degradation refers to the process of alteration of the glove material when they are used with chemicals and compounds with which they are incompatible.

In the cartoon on the left, a range of glove materials are shown for 2 different solvents IC and SA. With solvent IC there is no degradation of NRL and neoprene gloves while the other materials show varying susceptibility. Conversely with solvent SA, NRL and neoprene are easily degraded while the other materials are unaffected.

Permeation:

The concept that is perhaps most difficult for the worker to appreciate is that of substance permeation of gloves. Under these circumstances the gloves appear totally normal, yet the chemical compound penetrates the glove material and builds up in concentration beneath the glove. Here the hazard environment changes. Occlusion and sweating lead to over-hydration and maceration of the stratum corneum and altered barrier function. Greater exposure to the hazard results!

Permeation occurs in 2 different settings, penetration through defects and diffusion through the glove material.

Consider the blue rectangle in the diagram below as representing the glove material.

Permeation can occur by penetration. In this scenario chemicals applied to the outer surface of the glove penetrate through pinholes in the gloves to reach the inner surface. Testing for pinholes prior to use can screen for this.

Alternatively penetration occurs in rubber laminates of cotton, via microscopic cotton filament wicks, extending to the outer surface from the inner surface which provide easy access routes.

While these mechanisms are easy to understand, breakthrough time (BTT) is not. Gloves act as a barrier between a compound and the skin. In certain situations such as a surgeon in an operating theatre where the patient is protected from unnecessary exposure to potentially infectious agents and vice versa, this can be assured over a period of time. In industrial work break-through time is a major limiting factor to all glove use.

Any chemical applied to the surface of the glove, given a high enough concentration and long enough exposure will diffuse through the glove to reach the opposite side.

Glove selection in industry is guided by breakthrough times measured in vitro. Specialised chambers in which 2 compartments are separated by a piece of the glove material of known thickness are used.

The substance under test is applied to the one side of the chamber and the time taken for its detection on the other side of the chamber is used as breakthrough time.

This is a standardised measurement done in a laboratory. It is measured under static, fixed environmental conditions and does not reflect "in use" situation where concentrations vary, substances are seldom pure and the temperature at which the exposure is occurring varies as does the thickness of the glove material at points of stretching.

Recently techniques have been designed to measure breakthrough time (BBT) as occurs "in vivo" when gloves are in use. While these are not yet available as routine "in use" indicators they do offer some guidance as to when a glove must be changed. They have shown that BTT varies at different regional sites in the glove.

The test conditions used in this illustration are total immersion at 35ºC using nitrile gloves and the solvent xylene. The breakthrough time as given by the manufacturer was 70 minutes. This implies that the gloves could be used to protect against xylene exposure for 70 minutes after which they would need to be replaced.

Using special detection pads applied to the skin at different sites of the hand, a totally different "in use" picture was revealed. When pads were applied to the fingers (1-dorsal surface, 2- palmar surface), no xylene was detected after 5 minutes and only small amounts of xylene were detected after 15 minutes of "in use" testing.

More worrying however were the findings from the pads that were applied to the dorsal (3) and palmar (4) surfaces of the hand. After 5 minutes of use, significant amounts of xylene were detected in the pads, whereas similar amounts were detected after 15 minutes in the finger area.

What does this mean? It means that measurements done in the laboratory do not reflect "in use" breakthrough times. For the experimental conditions just discussed, breakthrough time should have been adjusted 15-fold from 70 minutes as per recommendation to <5 minutes as measured. This highlights the cost of relying on gloves for personal protection. Under the test situations described, gloves need to be changed more often than every 5 minutes. The economic sense of providing engineering controls rather than gloves is obvious!