The Definition of Nuisance Dust

Definition of Nuisance Dust

Nuisance dust is an older term for airborne particles that do not have a specific occupational exposure limit of their own and are not known to cause serious toxic effects at normal workplace levels. Examples can include dusts from calcium carbonate, gypsum, cellulose, some starches and other materials that are not otherwise regulated. Today, regulators and professional bodies prefer terms such as particulates not otherwise regulated (PNOR) or particles not otherwise specified (PNOS).

The word nuisance is misleading. These dusts are not harmless. At high concentrations, any dust can irritate the eyes, nose and throat, cause coughing, reduce visibility, overload the lungs' natural cleaning system and contribute to chronic respiratory problems. Some dusts that look like ordinary nuisance dust may also contain hazardous materials, and many can explode if they build up and are ignited.

Exposure Limits for Nuisance Dust

Several organizations set general limits for these particles:

• OSHA: particulates not otherwise regulated have a permissible exposure limit of 15 mg/m³ for total dust and 5 mg/m³ for the respirable fraction, as an 8-hour time-weighted average.
• ACGIH: recommends lower threshold limit values for particles not otherwise specified, of 10 mg/m³ for inhalable particles and 3 mg/m³ for respirable particles.

These limits only apply when the dust truly contains no material with its own, stricter limit. If the dust contains crystalline silica, metals, wood dust, flour or other regulated substances, those specific limits apply instead. See occupational exposure limit (OEL).

Hidden Hazards in So-Called Nuisance Dust

• Crystalline silica: stone, sand, concrete and some minerals can release respirable silica, which has a much lower limit. See silica exposure.
• Combustible dust: many organic dusts, including sugar, flour, starch, wood, plastics and some metals, can fuel flash fires and explosions when dispersed in air. See explosion hazard.
• Sensitizers: some dusts, such as flour and certain wood species, can cause occupational asthma.
• Contaminants: dust may carry metals, mold, bacteria or chemical residues from the process.

Controlling Nuisance Dust

• Identify the dust: check safety data sheets and test bulk samples before assuming a dust is low hazard.
• Measure exposure: use personal air monitoring for both total and respirable dust. See industrial hygiene.
• Control at the source: enclose transfer points and use local exhaust ventilation, wet methods or dust suppression.
• Keep surfaces clean: use HEPA vacuums rather than dry sweeping or compressed air, and prevent dust from building up on beams and ledges. See housekeeping.
• Protect workers: provide respirators such as the N95 respirator where engineering controls cannot reduce exposure enough, along with eye protection where dust irritates the eyes.

Example of Nuisance Dust

A building products plant bagged ground limestone, which managers had long described as nuisance dust. Workers at the bagging station often worked in a visible dust cloud. A new safety coordinator arranged personal air sampling and bulk testing of the product.

The results showed respirable dust above the ACGIH recommendation, and bulk testing found a small percentage of crystalline silica in one of the quarry sources. The plant enclosed the bagging spout, added local exhaust ventilation, switched to HEPA vacuums for cleanup and put workers in a respiratory protection program while the controls were installed. Follow-up sampling showed both respirable dust and silica well below their limits.

Frequently Asked Questions: Nuisance Dust

Is nuisance dust harmful?

It can be. Even dusts without specific toxic effects can irritate the airways and harm the lungs at high levels, and many contain hazardous materials that need closer control.

What is the OSHA limit for nuisance dust?

OSHA's limit for particulates not otherwise regulated is 15 mg/m³ for total dust and 5 mg/m³ for respirable dust, averaged over an 8-hour shift.

Why is the term nuisance dust no longer preferred?

It suggests the dust is only an annoyance. Professional bodies now use neutral terms such as particles not otherwise specified to avoid underestimating the risk.