Respirators #

To stay safe in poor air quality, you need a good respirator. When sourcing respirators look for:

• Filtration rating: You need N95 (good & widely available), N99 (better), or P100 (best, filtering close to 100% of particles). Medical masks, KN94, and KN95 are not approved by NIOSH and will not protect you. Note that N95, N99, & P100 are particulate filters and will not protect you from gases or vapors which may be present in wildfire smoke.
• Proper fit: Make sure the respirator seals all the way around. You may have to try multiple options to find one that fits your face. Masks cannot seal properly if you have a beard or significant stubble (mustaches are usually OK). The air you’re breathing should feel clean and have no smoky smell.
• Comfort: Finding a comfortable respirator is important since farm and other outdoor workers may have to wear the respirator all day during bad periods of smoke or pollution.

For more detail see Cal/OSHA’s advice on using disposable respirators.

Note: Disposable respirators tend to be harder to get a good seal and are usually less comfortable. Re-usable, refillable respirators have much higher reviews for comfort and seal. Re-usable respirators save money but need to be cared for, cleaned, and stored in a clean bag.

Note also: if you are protecting yourself or your workers from air quality hazards that are not strictly particulate, such as VOCs/organic vapors, ammonia, etc., you will need respirators rated for those contaminants. Half mask and full mask respirators offer the option of cartridges that filter specific vapors and gases from the air (other styles can also supply fresh air from a tank). For a list of the types of respirators available for different contaminants, see OSHA’s quick card on respirators and Cal/OSHA’s guide to respirators in the workplace.

Recommended respirators #

Disposable masks: Moldex 4620 N95 masks #

Pros:

• Ruffled design increases the filter surface, making it easier to breathe and talk and keeping your face cooler. 
• Soft foam seal around the edge and adjustable elastic head strap,  improving comfort and seal.
• Protective plastic mesh over the filter makes it more durable and longer-lasting.
• No valve, so these are usable for COVID precautions as well.
• Usually works OK with glasses.

Cons:

• Usually only available in one size, “M/L.”
• No metal clip to adjust seal on the nose, so if it doesn’t fit your face, you’ll have to find another option. (Moldex has brief advice on achieving a good fit: 1) use both straps, 2) check the fit, and 3) tighten strap if necessary.)

Price ~$5 each, in boxes of 10. Available widely online. See Gemplers.

Reusable/elastomeric masks #

There are various models of reusable respirators in “half mask” (doesn’t cover your eyes) and “full mask” (covers your whole face) configurations. Half mask options are cheaper and less cumbersome. (GVS Elipse P100 mask pictured.)

Pros: 

• Even cheap half mask respirators are usually more comfortable than disposable N95s/KN95s, and more expensive options tend to have softer rubber and a better, more adjustable fit.
• Cost more up-front but save money overall.
• Filters (especially cartridges) typically last much longer than disposable masks.
• Better, more consistent filtration. Easy to find P100 filters.
• Easier to get a good seal, easier to adjust for comfort. Usually available in sizes from small to large. Check manufacturers’ and vendors’ websites for sizing guidance.
• Exhalation valves help keep your face cool. Manufacturers offer exhalation valve filters and plugs if you want to use these for COVID safety, as well. You can also tape a medical mask over the valve if necessary.
• Very durable masks. Replacement parts are readily available, so they can be fixed and maintained over the long term.
• Cartridges are also available for VOCs (gasoline, solvents, paints, etc), ammonia (manure/confined animal spaces), welding fumes, etc. These are an essential part of a farm’s safety supplies.

Cons: 

• It can be hard to communicate clearly behind these masks, especially if you’re using a cartridge filter instead of a fabric filter. You may need to tip your mask open to talk.
• Users will need to wipe them clean between uses and store them in a clean bag.

Price: ~$20 for entry level masks, ~$50 for most comfortable masks. Filters range $7-20 per pair.

What to buy #

You will need to buy a mask and also compatible filters. Be sure to buy both, since they are often packaged separately. Filters can be “pancake” style or cartridge. Look for P100 filters. N95 filters are often only available as a “pre-filter” that attaches on top of a cartridge and can’t be used on their own.

Respirator body	Pancake style filters	Cartridge style filters

Reputable brands include 3M, Moldex, and Honeywell. Newer manufacturers include GVS, whose compact “Elipse” respirator only offers P100 filters and is highly rated for comfort and ease of breathing and speaking (note these are optionally available without an exhalation valve for healthcare settings, marked “source control”; make note of which version you’re buying).

Cheaper masks will have harder, less flexible rubber. More expensive masks will have softer rubber and other perks.

Where to buy #

Gemplers has a wide selection of half mask and other respirators, so you can compare prices and options. Other industrial suppliers like Grainger tend to charge more. The GVS Elipse is available at online retailers including Lee Valley and Woodcraft, as well as Home Depot under the Klein Tools brand. 

Clean Air Crew has more information on reusable respirators, including several N95 options recently developed for healthcare settings. Medical masks are not cheaper than the pre-existing options from 3M, Moldex, and Honeywell, and they lack exhalation valves.

Air filters #

Farm buildings are rarely well sealed and rarely offer relief if outside air is unhealthy. It may not be possible to sufficiently clean the air inside big, leaky farm buildings and achieve healthy air for indoor work, but we collect some resources here to help you evaluate your options and try to offer workers clean air breaks inside if necessary.

Assess your needs #

Office spaces and other indoor work spaces may be able to be cleaned so that workers don’t need to wear N95 masks inside (at least for wildfire smoke reasons). To determine how much capacity a filter would need to clean a space, compare the volume of the space (L x W x H) to the capacity of a filter unit (usually in cubic feet per minute, CFM). 

Example: Suppose a packing shed is 40’ x 40’ x 20’ high = 32,000 cubic feet, and suppose a particular model of air filter can clean 700 cubic feet/minute (which translates to 42,000 cubic feet per hour). That means that the filter can theoretically filter all of the air in the space up to 1.3 times per hour (a.k.a., 1.3 air changes per hour).

Aim for at least several air changes per hour. In the example above, you could use three of those 700 CFM filters simultaneously to achieve almost 4 air changes per hour; or you could use a higher capacity filter.

If a space is leaky, aim for more air changes: leaky buildings may experience several air changes per hour just from outside, meaning that any filtered air will be replaced with outside air at that rate. If a space cannot be effectively sealed, new, smoky air will constantly replace filtered air, and filtration will not work. Placing filters close to workers may help, but if you can’t adequately clean the air in a space, workers should wear masks.

Place air filters in worker housing. If housing has central AC or ventilation, make sure the filters are MERV13 or better. Reduce smoke intrusion into sleeping spaces by closing windows and doors and taking whatever other steps are needed.

Run any indoor filter for at least a couple air changes before unmasking indoors (e.g., if your filter can do 4 air changes per hour in a given space, 2 air changes would take half an hour).

Clean room #

If all of your work spaces are big and leaky, consider making a clean room ****in a space ****where workers can rest or eat. Smaller spaces and rooms that are finished will be easier to filter.

If in doubt, mask #

It’s hard to measure air quality indoors without specialty instruments. If in doubt, wear a mask. If you smell smoke or feel like the air is not clean, wear a mask. If you or anyone else experiences symptoms of exposure to smoke, wear a good mask, rest, and seek medical attention as necessary.

Buy or make an air filter #

Farm buildings and workplaces need more filtration capacity than homes and even other commercial buildings. DIY air filters perform well as long as the filter media is regularly replaced (about every 1000 hours of use in dusty environments) and the unit is properly sized to the demands of the space. The common box fan design performs well and is easy to build. Commercial air filter units are also readily available.

Image source 3dhandyman. See link to plans below.

Recommendations for DIY builds #

• Use a commercial-grade fan, which performs better and withstands heavy use. (e.g., Air King, ~$50).
• Make a cube-shaped filter (Corsi Rosenthal box) to increase surface area, reduce the resistance on the fan, and maximize filtration capacity. Put legs on the corners of the unit to raise it off the ground and place a filter on the bottom of the cube, as well. 
• Use filters with a rating of MERV 13 or higher. MERV 12 and lower will not remove wildfire particles.
• Consider using thicker filters to increase filter surface area and capacity.
• Replace filters regularly.
• Consider building a higher capacity filter that uses a larger fan and more filters (see links below).

Plans & resources on DIY air filters:

• How to clean the air from harmful wildfire smoke (Clean Air Crew) 
• 2 different styles of DIY filter + plans: box fan or drum fan (3dhandyman, who like many others offers pre-fab kits on Etsy)

NOTE: As stated above, particulate filters (e.g., MERV 13 and N95/P100 masks) will remove smoke particles (PM2.5) but not harmful gases or vapors. Follow emergency management guidance and advisories on air quality conditions.