Image courtesy of OHD

Sponsored by OHD

In industrial hygiene, few practices are as well-established as respirator fit testing. For many professionals, the process is second nature, and often, it’s built on condensation nuclei counting (CNC) technology. CNC has long been the default method in the industry, and for good reason: it’s effective, quantitative, and widely accepted under OSHA and ISO standards.

But just because something is familiar doesn’t mean it’s always the best fit for every scenario.

As workplace demands evolve, it’s worth revisiting the “why” behind our methods. Controlled negative pressure (CNP) technology offers unique advantages in certain environments—especially when speed, precision, and simplified logistics matter.

Both CNC and CNP are scientifically valid, OSHA-compliant technologies. Let’s walk through practical, scenario-based guidance to help you match the method to the moment and ensure the technology you rely on is the one best suited to the job.

Understanding CNC vs. CNP: A Quick Refresher

Before diving into application-specific guidance, here’s a brief refresher on the technologies:

• CNC uses ambient aerosol particles as a test agent. The device counts particles inside and outside the respirator during a series of exercises to calculate fit factor.
• CNP creates a negative pressure inside the mask and measures air leakage while the user holds their breath. It doesn’t rely on particles, and testing can typically be completed faster.

Both methods meet OSHA and ISO quantitative fit-testing requirements. The key is knowing which one aligns with your setting and respirator use.

Scenario 1: Oil & Gas and Heavy Industry—CNP for Speed and Simplicity

In oil and gas, petrochemical plants, and other heavy industries, most workers are issued elastomeric respirators. Testing tends to happen in remote sites or high-demand environments, where time, portability, and test reliability are critical.

Why CNP shines here:

• CNP does not depend on ambient particles or controlled environments.
• No consumables like particle-generating alcohol are necessary.
• Tests can be completed in under two minutes.

For industrial hygienists managing compliance across multiple work sites—or needing a fast, accurate tool for tight turnarounds—CNP-based devices like the QuantiFit2 often offer the cleanest operational fit.

Scenario 2: Occupational Health Clinics—CNC for Respirator Versatility

In clinics, employee health programs, or hospital-based occupational health departments, the situation is different. Staff may rotate between N95s and elastomeric respirators depending on exposure risk or job function. That dual-use reality requires flexibility.

Why CNC makes sense:

• CNC devices can test both disposable and reusable respirators.
• The technology is already well-integrated into clinical protocols.
• Particle generators can compensate for cleaner indoor environments.

Devices like AeroFit, which leverage CNC, help reduce the complexity of running a high-throughput testing program in a clinical setting. New to the market, AeroFit offers many features never seen in older CNC fit testers, like silent operation, particle generation management, and automated daily verification.

The Bottom Line: Match the Tool to the Task

Very few distributors offer both CNP and CNC technologies, which can make it hard to get balanced, use-case-driven guidance. At OHD, we work with professionals across every sector and understand that what works in a clinic may not work in a mine.

We’re proud to be the only global provider of both OSHA-accepted quantitative fit-testing technologies. So, whether CNC or CNP is the right call for your application, you’ll have the tools—and the science—to make the best choice for your team.

If you'd like help identifying the best fit-testing technology for your specific use case, try OHD’s Find Your Fit tool.