Controlling Odor in the Cannabis Space

Our latest episode of “Cannabis is a Good Neighbor” addresses odor concerns. Cannabis is known to have a distinct scent. Some people like it, some people do not. Cannabis Businesses must be considerate of the community, and a common concern amongst communities is the potential for odor outside the facility. Erik Gath joins Brian Anderson on this podcast episode to address these concerns. Erik Gath is Associate Principal at BLW Engineering and has worked in the cannabis space for approximately 5 years. Erik provides mechanical engineering support to cannabis businesses, and one of the main things he addresses is odor control. Below you will find some key takeaways that Erik touched upon during this episode, as well as the transcript. The episode is available for stream here! 

  • The odor becomes an issue when the air inside the facility leaves the facility. To ensure no odor is emitted, we must control the air escaping from the building. 
  • When it comes to controlling the odor, the starting point is building pressure and ensuring that air is not leaving the facility. People are quick to criticize older facilities that were not properly designed to control the odors. 
  • In greenhouse cannabis operations, greenhouse growers must get rid of the humidity. They do this by opening large flaps, and the humid air escapes while pulling in the fresh air. This poses issues because the humid air that is released has a cannabis odor which poses an issue for neighborhoods and further enforces the mindset that “cannabis facilities reek of pot; therefore, we cannot allow these in our neighborhoods.” 
  • When addressing odor issues in existing buildings, it is critical to find a path for the air, whether it be inside out or outside in. An ideal situation is a brand-new building where every room is properly sealed and is tested with blower door tests. There is then a single point of exhaust that is treated, and certain chambers are pressurized, causing the air to cascade into corridors and negative air space and then escaping through that single point of exhaust. When there is a single point of exhaust, you can control and treat it. There are many technologies on the market, but the technology is only useful if you are able to control the air. 
  • Different types of cannabis facilities create various levels and types of odors. Extraction facilities get the most complaints, especially when it is ethanol extraction, giving off a pungent odor.  
  • Retail facilities are not a top concern when it comes to odors. Dispensaries only have the product in the vault. Anything displayed is just a prop; therefore, there is no odor. When it comes to dispensaries, Gath mitigates potential odors by addressing the building pressure, putting an exhaust in the vault, and treating it with carbon filtration. 
  •  “Any concerns over retail stores stinking up the neighborhood I think should be minimal, and anything we do for odor mitigation is above and beyond” At a minimum, it is best to provide some building pressurization that will mitigate or reduce the odor effects. 
  • “So [Retail has]an exceptionally low impact, but I think we should talk about it because maybe people have concerns or misconceptions about what retail does. So really, it is the manufacturing where odors are generated.” 
  • Common odor mitigation methods:  
    • Carbon filtration – Carbon filtering is a method of filtering where activated carbon removes impurities using absorption. Carbon filtration is a proven technology and is a method used in many industries. It is imperative to use the correct filter – buying off-the-shelf pleated filters and spray painting them with carbon spray paint will not produce the same effect. They must be adequately sized to the correct airflow rates.   
    • Fogging – This method is implemented with carbon filtration. Once the air comes through the carbon filter before the air exits the building, a fogging system injects essential oils into the air stream. These fogging systems attack the terpenes mitigating the odor. 
  • Studies have shown that after incorporating fogging systems complaints decrease in areas with large outdoor cannabis farms.  
  • Terpenes are what give plants an odor. Basil for example has terpenes and that is what gives it its scent. It is the same for cannabis. Terpenes are classified as volatile organic compounds or VOCs. “I hate saying VOC because the V in VOC is volatile, so everybody gets nervous that the air they are breathing is going to smell of marijuana and are going to get a contact high, or a headache, or somehow have their health affected by this VOC.” Gath explains.  
  • As more of these facilities are developed, we can establish a standard for incorporating these technologies and begin to get municipalities to do baseline tests. In the future it is important we adopt guidelines to quantify this rather than have it be subjective.  
  • As Anderson says, “Good regulations make business easier”. Set regulations are what allow industries to operate. When there is a lack of regulation, it can create confusion and obstacles to operate. In some municipalities, facilities will be in operation, and the regulations will change and become more severe, leading to conflicts. Adopting the highest level of standards in a facility regardless of the town’s-imposed restrictions can futureproof a facility.    
  • To be a good neighbor, we need to get ahead of the curve and implement these practices instead of waiting for complaints before implementing them. Every time we move the bar up and establish better practices, it helps to destigmatize the entire industry and allow it to grow and benefit everybody.  


Cannabis is a Good Neighbor: Odor Mitigation Transcript:

Below is a transcript of the podcast episode, which you can listen to in full here, edited and trimmed for clarity and brevity. 

BRIAN ANDERSON: I am Brian Anderson Principal at Anderson Porter Design this is our 3rd podcast episode; Cannabis is a Good Neighbor. Super psyched to be back with Eric Gath engineer at BLW Engineers of Littleton Mass. Eric thanks for joining. This is Cannabis is a Good Neighbor, this is a theme that has come up in our cannabis work in the past 7 years. Anything we do must go through towns, accepted by municipalities, and just looking around at the impact this has on the industry is where this theme, Cannabis is a Good Neighbor, came from. We work together, we’ve done a lot of work with BLW, we have you as engineers on a lot of projects. So, we got some shared experience around odor control which is our topic of today. So, tell us about yourself, where your background is, how you got into cannabis and then we can get into some stinky subjects. 

ERIK GATH: Sounds good. So, I started with BLW straight out of college in 2004. A little background on BLW, BLW was found in 1999 we are a full-service MEPFP consulting firm, which is mechanical, electric, plumbing, fire protection. We design building systems for all types of commercial buildings, whether it’s large-scale multi-family buildings, office buildings, restaurants, all the way to clean rooms. So, prior to getting involved in the cannabis industry I personally was heavily involved in restaurants, large-scale multifamily, and some lab work mixed in here and there. So that’s a little background.  

B: Awesome, I just lost my voice I drank some water the wrong way. 

E: No worries, I can tell you a little bit about how we got into cannabis 

B: Yes! 

E: It’s kind of a funny story my daughter was born in 2014 and we sent her to daycare in 2015. That was right around the time where the medical marijuana industry was ramping up in Massachusetts. After being there for a year, in passing I talked to the owner of the daycare’s husband here and there. And he started asking me questions about mechanical HVAC systems. And I found out he was a facility manager at a cultivation facility in Massachusetts 

B: That is fantastic  

E: Long story short, he brought me in to tour the facility I met with ownership, they had a bunch of questions and they ended up hiring us to do phase two of the facility. And I have to say that was a turning point in my career where I learned so much on that project, designing the systems for that facility, sitting in weekly meetings, learning about the industry, there are so many intelligent people and innovative ideas I just developed a passion for the industry.  

B: That is awesome. So, we are in Massachusetts right, I’m not sure where all our listeners are, but a lot of those industries is started here, our legalization passed in 2012 for medical and what was it that got those facilities into trouble, I’m thinking about one facility that is located on a beltway, the 495 beltways near a commuter rail station, and they would dump there air out as a way of getting rid of the humidity. It created an enormous backlash in the industry around odor because greenhouse growers, that what they do they dump out humid air and pull in fresh. But from an odor control perspective that was a huge issue, because of the neighborhoods that they go into, it has an enormous negative impact. I know we are working on some projects where the planning board is involved, deeply involved, asking questions about what our plan is to mitigate odor. What are some of those lessons u learned early on how to do that?  

E: so early on, you hit the nail on the head. Building pressure is kind of the starting point for me as far as trying to control odors. If you are not controlling the air that is leaving the facility and you just have a positive pressure in the building and air is constantly escaping there is just no way you can control the odor. So, in those earlier facilities their medical, all-in industrial areas, you do not have a lot of concerns in these industrial areas, nobody really knew odors were going to have such an effect. So yeah, it raised some concerns and it’s kind of stuck in the industry. Because the earlier facilities that were open, there were a bunch of them, and for a while, there were no others. So, the only ones that you can point someone to are probably having those issues and a lot of the early ones might have provided some kind of early filtration, some type of low-level carbon filtration, but something that is not properly designed to control the odors. So, you can stick a pleated carbon filter in the building but if you are not controlling the air that is escaping from the building it going to have an effect.  

B: you know that is an interesting idea, that the building is pressurized inside, and that air is going to leak out. So how do you control that? From an engineering perspective, are there differences between renovating old buildings where you can control those leaks versus a new building? Give us a sense of how you control pressure as an engineer, and how that relates to odor.  

E: it varies from project to project as you said. Ideally, you have a brand-new building that you can properly seal every room and do blower door tests and you know that is the ideal situation we try to do that even on existing buildings, but what we do is we try and find a path for that air, whether it is inside out, outside in. You try and pressurize certain rooms, and have it cascade into corridors, negative air spaces, and try to have a single point of exhaust so that you can actually treat that exhaust. If you have doors opening and a positive pressure and air is escaping out the door, you are not treating it. We like to make sure we have control out of the exhausts and the ability to use one of these technologies, there are a ton of technologies that are available on the market but if you cannot control the air there is no way to use the technology.  

B: so, you mention cascading air effects that is a term of art that comes from FDA certification, so drug manufacturing plants, clean rooms, things that have Iso certification use cascading air effects. Does that mean cannabis facilities are FDA certifiable? Do you pull that mechanism from working in pharma or is it something achievable by many different facilities? IN other words, sometimes it sounds scary to talk about pharma and manufacturing standards from which GMP comes from – good manufacturing practices – but what I am trying to get at is cascading air effects which you mentioned is a method for controlling pressures and moving air through a facility, can that be done without the building being fully GMP certified? Or is that part of being GMP certified? 

E: Absolutely, that is ideal, that is the direction we like to push our projects. Some clients aren’t looking for that level of cleanroom or iso8 standards, they just want to get down and dirty, but we push them away from that. At a minimum, we are going to provide some type of building pressurization that will mitigate or reduce the odor effects on the neighborhood.  

B: So, what’s worse for odor, is a grow room impactful on odor? Or manufacturing MIP kitchen that is decarboxylating cannabis more impactful on odor?  

E: So that is 20 questions. It’s totally subjective. My opinions and what I have gotten the most feedback on is extraction facilities provide the worse odor. When some of my clients are doing extraction that has gotten more complaints than a typical flower room. Flower rooms actually a lot of people find the odor pleasant, me being one of them I actually like the smell. But when you are doing ethanol extraction it can give off a really pungent odor. But the flower rooms, typically the different terpenes that are given off, it’s subjective, but people like it.  

B: So, manufacturing and extraction produce more odor or different types of odor than cultivation, and how about retail? The other aspect of cannabis facilities is retail, and we do a lot of retail projects together so let’s talk retail for a second, what are the impacts you see in retail odor control?  

E: Retail facilities will try and go into a special permit and people are concerned about odor and people are concerned about people smoking marijuana outside the facility and all of these different effects. It is not a top concern of mine. We go above and beyond even by just providing that building pressure I spoke about, we typically put exhaust in the vault and then treat that with carbon filtration. Most dispensaries and adult-use marijuana retail facilities are all packaged, these things are childproof packaging, fully sealed, and won’t be producing much odor except maybe on the packaging since it has been handled. It should be minimal odor unless there is a return or something. So, any concern over retail stores stinking up the neighborhood I think should be minimal and anything we do for odor mitigation is above and beyond.  

B: So, the ccc regulates the entire industry and regulates the retail industry very heavily. And something many people aren’t aware of is the sales floor has no live product on it, in other words, anything in a display case on a sale floor is a prop, it is like a theater set, you can see the boxes but there is no actual product in it, there is no aroma producing product on the sales floor. So those doors can open and close freely and the only thing we are really worried about is humidity and temperature control in the wintertime. All the product you purchase from a retail store comes from the vault, and as you said it all comes to the vault prepackaged, transportation laws are very strict, labor laws are very strict, so all the product is coming in packaged, and then it gets dispensed. As a dispensary, it gets packaged into your orders, the ticket gets sent to the vault, they read it and fill your order and away you go. So, it is an exceptionally low impact, retail is a very low impact thing, but I think we should talk about it because maybe people have concerns or misconceptions about what retail does. So really it is the manufacturing where odors are generated. So, you manage them through pressure, you manage them through carbon filtrations, what are the others? I know you have a 3-part system that you have talked to planning boards, tell us about your three-step process.  

E: Sure, so like I said before I’m going to reiterate, you have to control the building pressure, where you are exhausting, be able to know where the odors are going in order to treat them. So, you start there. Carbon filtration is the most common it has been used for many years in many different industries, not just cannabis, it is a proven technology, it works. As long as you use the right filters. You can’t just buy off-the-shelf pleated filters that have been spray-painted with carbon spray paint. You need to properly size them at the right airflow rates and that is a pretty effective technology. But the municipalities take that and say ‘ok great you are going to filter it with carbon, and we are going to give you your special permit’ typically they want to go above and beyond. So, we will incorporate a couple of different technologies, one being a fogging type of system using essential oils, so after it goes through the carbon filter before exit exits the building this fogging type of system is injected into the air stream. There are others, perfumes, ozone, all different types of different technologies.  

B: yes, the fogging piece is huge in central California. Where central coast California to Santa Barbra north there are just massive massive greenhouses that have been taken over by the cut flower industry converted to cannabis grows, and they have flaps at the ridgeline where they just dump and exhaust air, so the impact on those from odor is massive. And what I have seen them do is use literally perfumes and fogging systems that attack the terpenes.  

E: There are studies that have been done that they were getting complaints from the neighbors, and they incorporated this system, and it essentially eliminated all the complaints – and this was for an outdoor grow, you’re talking a farm of marijuana, and after incorporating this spraying fog type system they had no issues.  

B: I don’t know if that is too geeky or too technical to talk about on this podcast is VOC, but I guess it is worth it because we are in the construction industry, and in my career, prior to coming to cannabis we did a lot of work with LEED certifications and VOC, which is Volatile Organic Compound. The general public starts to understand certain VOCs are in certain paints, so you’ll see in specs that there is VOC or no VOC paints. VOCs come in carpet, if proper carpets aren’t specified the whole room can smell for weeks after you install new carpet, that’s because of VOC, volatile organic compounds. The terpenes from cannabis are in fact VOCs and the terpene in basil is what gives basil the smell, you pick up a bunch of basil and decide whether to buy it you do that based on the VOC, the terpenes the plant gives off. So, cannabis gives off volatile organic compounds and so is that what carbon filtration and fogging have the ability to glob on the VOC and pull them out of the airstream?  

E: Exactly without getting into the chemistry of it because I’m a mechanical engineer, not a chemist. With carbon filtration, I think they call it chemical absorption so the carbon is able to absorb the VOCs and the same thing with the fogging system, actually with essential oils it can counteract those VOCs rendering it odorless. I hate saying VOC because the v in VOC is volatile, so everybody gets nervous that the air going to breathe the smell of marijuana and they’re going to get a contact high, or a headache, or somehow have their health affected by this VOC. 

B: it does right, if you do not understand what volatile means in this case, and in fact volatile is not volatile to the person but volatile to the plant and life cycle to the compound so we talk about shelf life. It is really important in cannabis, these terpenes are what give flavor and potency and various profiles to the product that our customers manufacture, and the volatility we are talking about here is the ability for them to break down or the speed at which they break down and dissolve and that is the piece that is volatile, it is not hazardous it’s not HACS they are VOCs. So, it is not the volatility there it has more to do with their shelf life than to the effect of somebody who breathes them in. So that’s interesting, that these facilities have both, well first and foremost, they have mechanical systems that monitor the flow of air, right? Very finely tuned mechanical systems that control the flow of air or the escape of air. Most of the facilities we design together are not greenhouses that have the big flaps on the top that just open up and dump air out of the atmosphere at night, but rather controlled environment horticulture. Where every cycle of air is monitored and controlled and is tempered. I think that’s one of the major points that I know planning boards ask all the time. So, this was something I wanted to cover on this episode with you because I can design a very very tight envelope, but I need assistance to make sure that the right cubic feet per minute and the right filter size and right penetration size, and the openings are all specified properly.  

E:  And I think it is important to be said too, is you and I have had to go to these special permit hearings, and they want you to quantify how you are going to eliminate or limit these odors. There are ways of test VOCs and monitoring, but I don’t see it being employed. They basically want you to say that it will be undetectable at the property line. But you are looking to fail there. At some point, you might have an odor.  So, I think that in the future once more of these facilities are developed and we establish a precedent where we are incorporating all these technologies, we can start to get municipalities that will do some sort of test like acoustic engineers do – they take a baseline level of noise and then they say ok after you open the facility, we will allow you to be 10 decibels higher. So hopefully in the near future, there will be some type of guidelines so we can quantify this rather than just have it be subjective and having a neighbor say I smell a skunk and having your client be liable.  

B: this is sort of a truism in any industry “good regulations, make business easier” solid regulations that can be read and interpreted are what allow industries to operate. It is the lack of regulation that makes it confusing and difficult to operate. The question I guess is, what would you advise, how would you advise an entity to choose a location? Would you advise them to read the planning board’s bylaws before choosing a town in which to operate? Or would you advise a town to revise its bylaws to anticipate how they want to regulate the industry? 

E: Just have them call me and I will take care of it. Ha ha. Honestly, that is a great question because it is the end of prohibition. These cultivation facilities and retail stores are starting to pop up everywhere, and municipalities are just trying to figure them out, they try and talk to other municipalities, and they are constantly evolving their regulations. Some facilities are already in operation, and they are changing the rules, so it is difficult. The idea would be is to just design it the best way possible and assume that regulations will get more sick and also set a precedent for the rest of cultivation facilities and retail facilities in Massachusetts right from the get-go, instead of adapting. 

B: Great advice ‘adopt the highest level of standards, regardless of what the town imposes.’ Good practices are being set there are good things you can do, that is good advice. Before we wrap up, any last thoughts? This has been a great piece because the odor is such a major part of facility design when it comes to both having entities, cannabis entities, understand their responsibilities are and having planning boards understand what their options are. Any last thoughts? 

E: Not really. I guess just reiterate the fact that in order to be a good neighbor we need to get ahead of the curve, and we need to implement these practices that are kind of new and make sure they are implemented ahead of time instead of waiting for a complaint to fix it. 

B: right because every time we move that bar and establish a better practice it really helps take the stigma away from the entire industry. It allows this entire industry to grow and benefit everybody.  

E: there are so many health benefits but there is still that stigma and having a facility that produces this marijuana odor that some people don’t like, is not helping us reduce that stigma.  

B: well, eric thank you, BLW Engineers, Littleton mass, we love your work, great support, and good engineering as a company. Thanks for your help, thanks for joining us in episode 3 on Odor control for Cannabis is a Good Neighbor. Take care! 

E: Excellent thanks a lot!  

This is a podcast series brought to you by Anderson Porter DesignBrian Anderson is joined by cannabis industry experts to discuss concerns of cannabis in the neighborhood. Our goal is to provide industry experts with information regarding sustainability, best practices, and challenges they may face with communities while working in cannabis. We also hope industry experts will use this podcast as a resource to share on a local level to educate communities and lawmakers about what they can expect by having cannabis as a neighbor.



Brian Anderson


Principal, Co-Founder

Anderson Porter Design




Erik Gath



Associate Principal 

BLW Engineers