Tag Archives: public health

Risk Reduction Engineering for COVID-19

Posted on by

In response to some discussions I had seen about the use of HEPA filters to help with the COVID-19 crises, I wrote some thoughts on how effective I thought HEPA might be. Several people on Twitter stated they agreed with my statements. An HVAC technician (@JSTootell) provided some thoughts that I had never even considered such as the energy requirements on the buildings where a HEPA filter is installed as HEPA requires more energy (i.e. electricity) to run than normal HVAC filters. He also said the normal air velocity is super low because if you increase the air velocity and hence get more circulation, people complain about the noise of the air through the vents.

Some others have noted that HEPA filters, on a whole HVAC system or portable units in each room, won’t hurt to which I agree. One said they should be a part of a multiple layer approach to prevent the spread of COVID-19 to which I also agree. In fact, while I did not say it, that is part of my argument, HEPA filters alone will not solve the problem of COVID-19 transmission. I want to take a step back though and discuss this from an engineering perspective.

The basic, general idea in engineering is you find out what your design specifications are, you make some calculations and draw some designs to comply with those specifications based on proven information, you throw in some safety factors, and then you build whatever it is to comply with your design and calculations. If you want to build a bridge, you need to know before hand what are the design specifications. Is it for trains, vehicles (cars and trucks), pedestrians, or something else entirely? How many of the intended type of users will be crossing the bridge daily? What is the span of the bridge? What is the height of the bridge? What type of weather will the bridge will be exposed to? There are far more questions, but that is the general idea. You can’t design a bridge until you know what you are designing.

I currently work in human health risk assessment related to exposure to hazardous chemicals. It is not the same as risk assessment related to exposure to infectious agents, but there are similarities. With hazardous chemicals, the goal is to reduce people’s exposure such that they are not at undue risk to the chemical exposure. You can’t reduce risk to zero; it is simply impossible. With chemicals that cause cancer, generally you are trying to get the risk below one in a million chance of cancer caused by exposure to that chemical. Another part of this is who is at most risk. With chemicals, the people we are generally most concerned with are children or pregnant women as they can be more susceptible to harmful effects than healthy, non-pregnant adults. The risk requirement is one of your design requirements. If a person can be exposed to 100 mg/l per day (via ingestion) or 100 mg/g (via inhalation) of a certain chemical and not be above one in a million risk of cancer, then you have to figure out what needs to be done at a contaminated site or with contaminated drinking water to get their exposure (and thus risk level) below that number. This could mean filtering water or removing topsoil at site (to avoid incidental ingestion of contaminated soil or to avoid breathing in soil particles). What kind of treatment and how much treatment is needed to get below that concentration? That is one of your design requirements. Similarly the design and operation of water treatment plants is based on cleaning water such that the water has less than some amount of a contaminant before it is sent via pipes to the customers. Design requirements from water treatment plants is generally based less on risk calculations and more on state and federal requirements for contaminant levels in drinking water. These federal requirements are called Maximum Contaminant Levels. Water treatment plants must meet these requirements, and they are designed to prevent the people who drink that water from getting sick from microorganisms or chemicals in the water.

This leads me to designing a HVAC system with HEPA filters or the use of portable HEPA filters in buildings to protect against COVID-19. In order to design a system, you have to know the design requirements. It is absolutely fine to say you want to reduce virus particles in the air and reduce transmission, but that is not a design requirement. Reduce is a vague, qualitative word. Engineering requires quantitative requirements. If you only want to reduce particles in the air, then you will only reduce the risk by an unknown amount with no clarity on if that reduction is an acceptable amount to the occupants of the building. Reducing risk could mean that instead of 30% of the occupants of a building getting sick, only 20% do. I personally don’t find that to be an acceptable reduction. A design requirement is based on what concentration of virus particles can be in the air and no person gets sick from COVID-19. Perhaps your requirement would not be that stringent, perhaps you would be ok with one in a thousand people getting sick from COVID-19 based on the design. The design requirement can be based on people wearing a mask or not wearing a mask. Maybe with everyone wearing a mask indoors, they can be exposed to 10 virus particles per hour, but without a mask, they can only be exposed to 2 virus particles per hour. This is where infectious disease experts are needed to provide information as to the pathogenicity and virulence of the pathogen, which in this case is COVID-19. An engineer designing a HVAC or some other filtering system for a building is not the person to decide what those design requirements are. They need the infectious disease experts to state what concentration of a pathogen a person can be exposed to without getting infected. The concentration may be zero. The problem at this point is I don’t think we know how much COVID-19 a person can be exposed to without getting sick. Thus, if we don’t know how much COVID-19 a person can be exposed to without getting sick, how can we possibly design a system to prevent a person from getting sick.

I can already hear arguments that we just need to do something. We need to accept some risk but do some things to reduce risk, so we can get things back to normal. I don’t think most business owners are going to be willing to spend a non-negligible amount of money on some design that will simply reduce risk to an unknown and unproven amount. For a place of employment or a school, is it reasonable to ask people, especially children, to return to a building with an unknown risk if a system has been put in place that reduces the risk an unknown amount? How much money should employers and educational boards spend to reduce risk an unknown amount? If you are willing to accept some risk, then why spend money on something that may reduce risk by some unknown amount? Everyone is already spending money on masks, gloves, hand sanitizer, etc. which at least has been proven to reduce risk, but not eliminate it, by a reasonable degree from a cost benefit perspective. I spent $20 or something on two reusable cotton masks that I wash after use. That is a very reasonable cost benefit amount from my perspective even though I can’t calculate the risk reduction of the mask. How much money is reasonable to invest in either a whole system HEPA filter or portable HEPA filters when the risk reduction is unknown? An extremely quick internet search provides options for portable HEPA filters from $200 to $1200. Should schools buy one per classroom, even at the low price end, when there is no data to show they would reduce risk at all? The point is, reducing risk is good, but if you going to invest money to reduce the risk, it would be prudent to determine how much the risk is actually going to be reduced before you do it.

PPE Basics

Posted on by

People are scared by COVID-19. This is understandable. Some people have started wearing personal protective equipment (PPE), mainly masks and gloves, although some are going for bonus points PPE like protective overalls, because they think the PPE will help protect them from COVID-19. It may, but it may not. I thought I might present just a few basics points for people who don’t normally wear to consider about wearing PPE.

What do I know about PPE you may ask. I am engineer and scientist. I have worn PPE in the field when taking environmental and industrial hygiene samples including soil, groundwater, urine, blood, air samples, and more. To earn my Ph.D., I worked in a lab that handled both chemical and biological samples. That is, one day I might have been handling urine or blood and needed to protect myself from pathogens, and another day I might have been handling chemical samples (or more likely part of a biological sample that had been placed into a chemical for processing) and needed to protect myself from chemical hazards. I am also HAZWOPER certified, and as part of the training, you have to dress in Level A and Level B PPE.

The most basic thing you need to know about PPE is first that PPE is essentially anything you wear that protects you from a hazard. In some places, jeans and long sleeves are PPE because they cover your skin from minor hazards. Steel-toed, leather boots are PPE that I have worn on a frequent basis when in the field as they protect my feet from many physical hazards including in at least one location I was working, rattlesnakes. [Not a hazard I was expecting on that site inspection, but, well, Texas.]

The second most basic thing you need to know about PPE is that it is not magical. PPE has to be worn correctly, and the correct PPE must be worn. For example, not all gloves protect against all hazards. In most of my work, I have worn nitrile gloves. Nitrile tent to be preferred over latex. The minor reason is potential latex allergy. However the main reason is that nitrile protects against more chemicals than latex. For most of my work, it is chemicals for which I need to protect myself. Most gardening gloves will protect you against some physical hazards like prickly vines, but they will not in general protect you against chemicals like pesticides you might be applying.

On the subject of gloves, gloves do not kill bacteria or viruses. If you are worried about viruses getting on your hands because you are touching a grocery cart for example, and so you decide to wear nitrile gloves, if you dispose of the gloves after touching the grocery cart and don’t touch anything else, then gloves may have protected you. However, if after touching the grocery cart with the gloves, you then touch your phone or your face with the gloves, then the gloves have done you no good. You have just transferred any viruses from the grocery cart to your gloves to your phone or face, just as efficiently as if you had not worn gloves. A week ago, I went to Costco and went first to the bathroom. When I was washing my hands, I noticed a woman washing her hands while wearing latex gloves. I simply don’t want to know what else she touched with the gloves before doing this or after.

A final note about gloves, there is a definite technique to how to remove them. The goal is to remove them without touching the outside of them. There may possible be another way, but the best way I have found to do it, is place one gloved finger on the outside of the other hand’s glove, near the wrist and carefully pull that other hand’s glove off, sort of rolling it off. Then with the now glove free hand, place your ungloved thumb under the other glove near the wrist and pull that glove off. Easier to show than explain.

Masks and respirators are designed for different types of protection, and it is critical that they be worn properly and for the correct use. Surgical masks are really more to the protect the patient from the surgeon sneezing or coughing on them than to protect the surgeon from the patient. Surgical masks can protect the wearer from splashes or larger droplets or to a certain extent large particles, but that is about it. Surgical masks do not provide even a decent seal around the face, so they do not protect from airborne viruses, bacteria, chemicals, or even small particles. If you don’t believe me, believe the FDA.

The now popular N95 masks can protect against some particles, viruses, and some other things if worn correctly. First, it is important to consult the manufacture’s information as to what they are designed to do and not to do. Second, it is critical that the wearer has a good seal. What does that mean? It means the edges of the masks must fit snugly against the skin for the entire perimeter of the mask. Men, you have to be clean shaven. Even an evening stubble will prevent the seal. N95 masks have a piece of metal that goes over the nose. That metal needs to be adjusted to get a good seal over the nose. Both elastic bands for the mask must be used to increase the fitness of the seal. Finally, masks get saturated. They can only be worn for a certain period of time before whatever you are breathing in breakthrough the mask.

I can’t emphasize enough how critical seals are. When I was graduate school, for the field work I was doing, I needed to be able to use a half-face respirator. That required me to first get medical clearance to wear the respirator. Second, I had to be fit-tested for the specific respirator I was going to wear. Different manufacturers make different size masks, and they don’t generally agree with each other. Hence I was fit-tested to wear a specific manufacture’s specific sized mask, and that was the one I wore throughout my field work.

Finally with respirators and masks also, the manufacture will state what the respirator or mask is designed to protect you from. If you go to a hardware store and look at respirators, you will notice that some respirators are for lead, some for particulates, some VOCs, and some will do a combination. A mask to protect from VOCs and PM10 is common. If you are going to work with VOCs, and you get one that is only for PM10, you will not be protected at all. Cartridges for respirators have to be changed frequently. Every two weeks is a common changeout time.

Those are the basics. There is really a lot more to understand about PPE, but those of the initial basic critical points to understand if you are thinking about wearing PPE to protect you from a virus or other hazards.

COVID-19 Environmental Effects

Posted on by

For three days following September 11, 2001, civilian planes were grounded in the United States. It has been postulated that the diurnal temperature range in the U.S. was affected by the lack of contrails created by planes. Contrails, condensation trails, are formed by planes flying at high altitudes. It has been hypothesized that they can act as natural cirrus clouds for at least a short period of time after they form by absorbing long- wave radiation at night and reflecting more shortwave radiation into space throughout the day. Hence they can affect temperatures. The theory that the lack of contrails for three days following 9/11 affected the weather has been disputed though. The three days following the attacks formed a natural experiment that scientists looked at after the fact, but because the planes were only down for three days, that is not much time to have enough data.

Almost the entire world is in the middle of an unprecedented event because of the novel coronavirus often referred to as COVID-19. Anyone who can telework is. People are unfortunately getting either laid off or furloughed because the tourism and entertainment industries have taken such a hit. Restaurants are being forced to close or are only offering carryout service. People are not traveling if they don’t have to either to commute or to go to another city. Governments across the world are telling people to stay home if they are able, or in some cases are ordering them to stay home.

What effect will this have on the environment? Northern Italy has been hard hit by the virus. People in Venice are reporting that the water is the clearest it has been in decades. They are attributing that to the lack of boat traffic. At least initial reports seem to indicate that air pollution has decreased because of lack of vehicle traffic. I am curious though about all the impacts. Vehicle traffic would seem to be the most obvious. Most people are not leaving their house unless they have to, but deliveries may be going up. Airline traffic is definitely down. Train travel is probably down. Inner-city buses and subways are decreasing service due to decreased demand.

What are the other effects though? Water usage may not change in total, but I would hypothesize that it may change temporally. There is a general routine on weekdays. People wake up. Many take showers. They leave their house and go about business. They come home and then start housework among other things like running the dishwasher. Perhaps they do laundry, or perhaps like many the laundry is done on weekends. If a significant portion of the population is teleworking or just plain told not to come to work, they will probably run washing machine or dishwasher in the middle of the day between conference calls. Thus water demand instead of peaking in the early morning and then again in the evening may average out across the day. Same for wastewater flow.

Electricity may be even more interesting. In the early morning and late evening, more electricity is used by people in their residences. In the middle of the day, more people are at businesses or schools, so they are using more of their electricity there. Similar for telecommunications. What about when everyone is staying home and teleworking? In theory, the offices should use less electricity assuming there are smart devices there to not turn on lights if no movement or the HVAC reacts to need in the offices. However, the homes are probably using more electricity. How will this affect the electricity grid? Electricity needs will be more spread out around residences and less in concentrated urban areas. The high speed internet at the office is probably not going to be used as much, but will the internet from residences be strained from all the traffic? My employer has been having remote access issues, which I have no doubt stem from the number of employees working from home. How will this affect the telecommunications grid? Cellphone traffic will possibly go up, and landline traffic may go down.

Conversely, will trash be generate less, the same, or more trash? Not going out would in theory generate less trash. However, we are probably going to go through more gloves, masks, and other personal protective equipment in the coming months, and not just from medical personnel. Take out from a restaurant generates more trash at least from the consumer than eating in, but as people avoid restaurants in general, no trash is being generated there.

I am not in any way shape or form arguing that the virus may be good or bad for the environment. People are dying. I am not losing sight of that. However, I think it is likely that the virus will affect the environment, and I am curious how. It seems likely that self quarantines or at least staying home as much as possible may last weeks if not months, so that may be an adequate amount of time for an affect of some sort to be seen. Question is, what will the affect be?

F.J. Horgan Water Treatment Plant

Posted on by

The F.J. Horgan Water Treatment Plant was one of my top two reasons for coming to Doors Open Toronto. Sadly, no wastewater treatment plants were open for the event, as I find them more interesting than water treatment plants. However, water treatment plants are still interesting. This plant was even more interesting than I initially thought it would be because I am fairly this is the first water treatment plant I have been to where they use ozone for the initial disinfectant. This is the second water treatment plant I have visited in Toronto. The first Doors Open Toronto I came to, I visited the absolutely magnificent R.C. Harris Water Treatment Plant. F.J. Horgan Water Treatment Plant is not as beautiful, but it is interesting none the less.

The plant’s water intake is from pipes in Lake Ontario over 2 km from shore. It is then pumped to the plant and then up from the pipes which are (I think) nine stories below the surface. The plant sits on cliffs high above the water surface. Ozone is added to the water. Ozone disinfects the water. The ozone is made at the treatment plant from liquid oxygen. Before the water leaves the tanks where is contacts ozone, sodium bisulfite is added to remove any left over ozone.

Ozone generation unit from liquid oxygen and electricity
Ozone is piped to water contact units

Coagulant is then added to the water. Coagulant causes certain ions and tiny particles to start to come together to make bigger particles, which are easier to filter out. The water is pumped to sediment filters. The filters have a lower sand layer topped with a carbon layer. The filter tanks are huge, but so are the pipes in the building.

Gigantic water pipe conveying water (I think) to the filter tanks
This is a horrible photo because is taken through glass with wire lining, but that is water in the filter tanks. The filters are at the bottom, and I think blue plastic thing is the trough where the backwash goes when the unit is backwashed.
Another horrible photo taken through glass, but on the left side is an empty filter tank, and on the right side is a filter tank with water.
Low pressure air pipes in the filtration gallery
Gigantic air pipes running through the main part of the building

After the water has been cleaned, chlorine is added. The water has already been disinfected at this point, but a residual disinfectant is needed to kill any bacteria the water may encounter in the distribution system on its way to customers.