Nanoparticle Exposure: NIOSH Updates Engineering Control Recommendations

The behavior of many common chemicals is, by now, predictable in most circumstances. But when a very common substance (for example, carbon) is broken down into individual molecules and rebuilt into an extremely tiny structure (for example, a tube of carbon “rings”), its chemical behavior is entirely differently from the same substance in a larger form.

These molecular-scale particles, which are generally 1–100 nanometers in size, are called nanoparticles. Because their chemistry is unique, they have different uses than their larger counterparts.

In fact, nanoparticles have a lot of uses. In consumer products alone, more than 1,000 products contain engineered nanoparticles. Makeup, sunscreen, food storage containers, appliances, clothing, electronics, computers, sporting goods, and coatings all incorporate engineered nanomaterials. Unfortunately, increasing applications for these materials means increasing exposure to their hazards for workers, and the control measures and exposure limits that work for larger particles won’t necessarily work for them.

In March 2016, the National Institute for Occupational Safety and Health (NIOSH) published Building a Safety Program to Protect the Nanotechnology Workforce: A Guide for Small to Medium-Sized Enterprises, which includes recommendations for controlling worker exposures (http://bit.ly/2i3Ayao). In September 2016, researchers from NIOSH’s Nanotechnology Research Center (NRC) presented its most recent engineering control recommendations at a meeting of NIOSH’s Board of Scientific Counselors (http://bit.ly/2gPaaQm).

Here’s a look at the latest recommendations from NIOSH for controlling worker exposures to nanoparticles.

Identifying Exposures

To protect workers, employers first must identify the circumstances that can create respiratory or skin exposure to nanoparticles. Exposure risk is affected by:

• The quantity of nanomaterials being handled or produced;
• The physical form and dispersibility (dustiness) of those materials; and
• The duration of the task.

As each one of these variables increases, the chance of exposure becomes greater. Operations involving easily dispersed dry nanomaterials, such as powders, will create greater exposures than those involving nanomaterials that are suspended in a liquid matrix or embedded in a solid.

The NRC researchers found that the greatest potential for worker exposures results from:

• Leakage from reactors and powder processing equipment
• Manually harvesting product from reactors
• Dumping/mixing of powders
• Replacing “big bags” (bulk containers) of nanomaterial-containing powders
• Spraying of liquids containing nanomaterials
• Weighing out powder/packaging material
• Changing filters on dust collection systems and vacuum cleaners

Controlling Exposures

NIOSH’s recommendations for controlling exposures follow the industrial hygiene hierarchy of controls. Wherever possible, potentially hazardous materials should be eliminated from the process. Failing that, less hazardous materials should be substituted for hazardous ones. If nanomaterials can’t be eliminated or substituted, engineering controls are the third choice for protecting workers.

Engineering controls isolate the process or equipment or contain the hazard, and the recommended controls vary somewhat depending on the form of nanomaterials.

For powdered nanoparticles, NIOSH recommends enclosure of either the process or the task. Examples include the use of screw-fed or pneumatic handling of materials in a closed system.

For liquid nanoparticle suspensions, routine operations are less risky, but the likelihood of exposure can increase significantly if the suspension is aerosolized through sonication or in unexpected situations, such as a spill. For these types of operations or tasks, NIOSH recommends enclosing that part of the process.

For nanomaterials incorporated into bulk solids, risk should be minimal except when the solid material is cut, sawed, drilled, sanded, or handled in a way that creates a dust or releases the nanomaterial. Local exhaust ventilation should be used for these operations.

For waste materials, NIOSH recommends sealing contaminated waste in bags to prevent the release of nanoparticles. Specific waste-collection activities may require specialized controls. When changing filters, for example, NIOSH recommends a bag-in, bag-out system, using bags with integral gloves, to remove and replace the filter. The bags then cinch closed for disposal.

When disposing of wetted wipes used to clean work areas, the wipes might release nanoparticles when they dry out. Wipes, therefore, also should be disposed of in sealed bags.

Practice Tip

Small quantities of nanoparticles should be handled in a lab hood, biological safety cabinet, nanomaterial handling enclosure, or glovebox, depending on the other hazards that may be present.