Respirator filter expert Simon Smith explains what’s in a mask and what drives personal protective equipment R&D

Simon Smith has a long history of developing personal protective equipment (PPE) for industrial, health-care, military, emergency response, and other applications. He specializes in respirator filters and says he finds great satisfaction in the opportunity to apply “dry” science to products that improve health and safety and sometimes save lives.

Smith, 60, earned a bachelor’s degree in chemistry from what is now Imperial College London, then a doctorate in chemistry from the University of Manchester Institute of Science and Technology in 1985. After a postdoctoral fellowship at the Royal Military College of Canada, he joined Racal Health and Safety. The company was purchased by 3M in 1998.

Smith retired from 3M in late 2019 but remains active in standards development with the International Organization for Standardization, the CSA Group (formerly the Canadian Standards Association), and other national and international health and safety organizations.

Jeff Johnson spoke with Smith about developing respirator filters to protect against chemicals as well as pathogens such as SARS-CoV-2, the virus that causes COVID-19. This interview was edited for length and clarity.

Are there general categories or types of personal air-filtration systems?

There are two main filter categories based on hazard type: particulate or gaseous matter. The effectiveness of these filters relies on filter media, sorbents, and reactive materials.

Particulate matter, either liquid or solid, is generally captured using fibrous media. Capture depends on several mechanisms, including electrostatic forces. It is the combination of several mechanisms that makes filters effective for a wide range of particle sizes. It is a mistake to think they are just fine sieves, and their broad capability means that a well-fitting respirator is highly effective against biological challenges like COVID-19.

For gases, filtration depends on either adsorption—using highly porous materials to capture and retain gaseous hazards—or chemical reaction to convert the gas into a harmless or involatile compound. The sorbent of choice for organic chemicals is activated carbon, usually derived from coal, peat, or coconut shells processed to enhance porosity.

For filtering inorganic gases, approaches include chemically treating sorbents to provide a high surface area for a material to react with specific substances or using catalysts to encourage reaction. The challenge in filter design is balancing multiple performance requirements with constraints such as filter size and breathability.

What if the toxic hazard is unknown or you need to capture a broad mixture of gases?

First, the use of filtering respirators should occur only where adequate oxygen is available and where hazard concentrations are known to be not immediately dangerous or overwhelming.

An example where hazards can be unknown is an act of terrorism. The Tokyo subway attack in 1995, for instance, raised awareness of such threats: the nerve gas sarin was used but not identified immediately. As a result, some rescuers approached the subway with just dust masks. Twelve people died on-scene, and several thousand were affected. This flagged the need for a respirator system ready to address a very broad range of hazards for first responders. It also blurred the distinction between military and industrial respirators, since first responders face both types of hazards.

In the late 1990s, we developed and patented novel filter concepts, called CBRN [chemical, biological, radiological, and nuclear] systems. These are layered protective systems. While they don’t address responders’ need for adequate oxygen, they are still useful for decontamination and emergency medical teams during a terrorist attack or chemical accident.

What have you learned through the COVID-19 pandemic?

For a decade before COVID, I was fortunate to work on standards expert committees, creating guidance for selecting respirators for airborne biological hazards in anticipation of pandemic needs. Despite available scientifically based guidance, the medical community largely still followed outdated thinking on aerosol transmission, and that resulted in inadequate protection for health workers.

For instance, surgical masks are widely considered protective. But they do not seal to the face and are only intended to be used to trap matter released by the wearers—not to protect them.

And for approved respirators, authorities have made a false distinction between medical and industrial types that in fact offer equivalent performance. This has sometimes led to an unneeded search for medical filters and consequently artificial shortages.

But COVID has also increased the focus on effective protection that comes with what I call the three Fs of PPE: filtration, fit, and function. Fit and filtration are obvious, but function is more complex—it includes the ease of breathing and communication while wearing a mask. Consequently, COVID has led to new product standards, and we are seeing new designs that are comfortable and cheap and also allow the wearer’s face to be visible, which benefits communication.

Is it correct that wars, industrial disasters, terrorist attacks, and now COVID-19 have been primary drivers for better PPE?

Unfortunately, that has often been the case. For instance, use of gases as weapons in World War I caused rapid protective equipment development. That later spun into protective equipment for industry, benefiting people often working in hazardous conditions in chemical plants.

During World War II, use of chemical weapons was expected but never happened. However, research undertaken in anticipation led to development of improved sorbents. Later, the Japanese subway attack demonstrated the need to develop respirators to protect against a broader range of hazards and to remove the distinction between military and industry applications.

The Fukushima Daiichi nuclear disaster in 2011 then revealed the need to develop better protective equipment for nuclear and chemical releases, spurring work on new international standards.

On the biological side, after the SARS outbreak in 2003, a Canadian commission urged reforms including application of the precautionary principle to prepare for similar future outbreaks. The recommendations included using greater caution, limiting travel, and better respiratory protection overall in health care. However, the reforms at first were not observed when COVID arose.

The new pandemic has demonstrated a strong need for safe, comfortable, inexpensive, and readily available PPE, particularly for health-care workers. It also has shown the importance of respiratory protection principles and the need for better public communication. Let’s hope the lessons have been learned.

Jeff Johnson is a freelance writer based in Washington, DC. A version of this story first appeared in ACS Chemical Health & Safety: cenm.ag/simonsmith.