Fall 2020 Design I Final Competition

Section M: Plague, Inc.

Problem Statement: How might we keep tables consistently clean before and after use in Mines Market?

Team Members: Robert Warkentine, Malcolm LaForce, Ricardo Quiroga, Joshua Krause

Instructor: Traci Case


  1. Hello Plague, Inc.

    I appreciate the high level of working prototype you constructed.

    Is there concern about the level of over spray that may land on surrounding surfaces like the floor? Could this cause a slip hazard if not wiped up properly? I typically see cleaning staff sanitize tables and chairs, but cleaning the floor between customers is not reasonable.

    How is the device powered? Would each table need an outlet? How often does the sprayer need maintenance or or a refill?

    Are there risks involved with the level of disinfectant aerosols in the air? (not wearing a mask while we eat)

    Besides Mines Market, are there other applications for this product?

    Thank you,
    Garrett Erickson

    • Regarding the refill timing of the TSA, I have calculated that based on 30 minutes per meal that is eaten due to Mines Market restrictions and the restricted flow rate of the pump, the container would need to be refilled once every day at the end of the day. This is because of the current 13 hour uptime of Mines Market, including rush hour and downtime, but the refill timing is subject to change based on the size of the table and the disinfectant used.

    • Hello Garrett, thank you for your questions! I can answer the first two for you.

      “Is there concern about the level of over spray that may land on surrounding surfaces like the floor?”

      In a final product, we would ideally have either a motor to change the angle of the spray nozzles, or an adjustment on the nozzles themselves to adjust the pressure of the fluid based on the size of the table. Such an implementation was a little too ambitious for the first prototype, but would certainly be added into the final form of the TSA to avoid a situation like you described. This would also make longer tables more easily sanitized.

      “Could this cause a slip hazard if not wiped up properly?”

      Based on our testing, the mist is very fine and diffuses more as the distance from the spray nozzles increases. Assuming risk mitigation for over-spray was not implemented, this could pose a potential risk for smaller tables, but not as much for larger ones with more surface area. However, adding angle adjustment or pressure-changing features to the nozzles would remove this hazard from the equation.

    • “How is the device powered? Would each table need an outlet?”

      As stated in the video, the TSA uses four rechargeable D batteries to power the Arduino and lighting system and eight AA batteries to power the sanitizer pump system. Because the entire system is battery powered, no, each table does not need an outlet.

    • As far as other applications for our product go, there are a lot of possibilities. Our product was designed for the Colorado School of Mines dining hall, but luckily the space does not differ much from other dine-in facilities. Our product can be seamlessly integrated into the cleaning procedures of most dine in restaurants, the dining halls/cafeterias of other college campuses or primary and secondary schools, and even in office spaces where people meet around a table or shared platform that would need to be cleaned after use.

  2. Hi Team Plague,
    i totally agree with you on a need for a better solution of sanitation of tables in restaurants. You have identified a great problem and made great strives towards a solution. I especially like the automated nature of your solution eliminating the need to wait for overworked staff to wipe tables.
    I also like the idea of a lamp – very convenient for identifying a free table similar to parking garages.
    I have one major concern:
    Many sanitizing solutions are not fully save for humans, e.g. a recent survey of hand sanitizers found methanol, a cancerogenic, in 75% of hand sanitizer brands tested. This could be especially problematic in an eating environment since customers may accidentally ingest it, potentiating the health hazard.

    • This is an excellent point and a valid concern! A solution to this issue would be using methanol free disinfectants that have been rated for food contact surfaces, such as the Purell brand food service disinfectant. By utilizing the available safer disinfectants we can mitigate and remove the harm of potential ingestion of the product so that the benefit of removing viruses from the table outweighs any risks from the lingering disinfectant. Additionally, with there being an allocated time for wiping off the tables, the staff would remove most of the leftover disinfectant, leaving little risk of substantial contact with the guests, while still seeing a reduced workload through eliminating the need for spraying and signaling.

  3. Hi Team,

    I really like the idea of the automated lamp signaling for cleaning tables, and it was an excellent prototype demonstration.

    At the current unit cost, it seems like this could be expensive for an institution to implement across campus, how would you justify the costs/benefits to your stakeholders? Or did stakeholders provide any specific price point feedback?

    Does the unit need to be plugged in? If so, would there be risk of a tripping hazard from cords or from the liquid pipeline that would need to be mitigated?

    • Patricia, thank you for your questions! I can answer your first set regarding cost/benefit. We were not provided any specific price point feedback, but the current unit cost could be lowered with increased manufacturing. However, it’s certainly still an investment. The main cost justification is much-improved sanitization consistency. Mines has been setting an example for the entire country in this pandemic, with a low infection rate and staying open for the entirety of the semester – something that can’t be said for many other schools across the US. However, the dining system in Mines Market could be considered a weak point of the otherwise-strong pandemic response. Mines and other schools with similar success would benefit significantly from improving sanitization in their dining halls, which has a high likelihood of further reducing the on-campus infection rate. This would help create confidence in students’ safety, creating more incentive for students to live on-campus and even enroll in the university to begin with. These benefits would be further amplified for schools that were forced to shut down due to high infection rates, easing safety fears of both parents and students.

      Other benefits of investing in this solution would be easing the workload of dining hall staff. Instead of watching for students to sit down, manually taking signs, and then wheeling a cart over to fully clean the table, the staff simply must look out for a blue light and wipe down the table with a cloth. This removal of manual intervention also greatly reduces the time spent cleaning tables, allowing students to move in and out of the dining hall in a more efficient manner. And naturally, improved dining sanitization is a significant benefit in and of itself, especially when the current system has proven to have many flaws.

    • I can answer the power aspect of the question. As stated in the presentation, our system uses four rechargeable D batteries and eight AA batteries. The D batteries are used to power the Arduino and the lighting system, while the AA batteries are used to power the sanitizer distribution system.

  4. This could be a very useful idea, I am intrigued. Overspray and any chemicals that might linger and be ingested is definitely something to address. Looking forward to more of your solutions (pun intended)!

    • Regarding your question surrounding lingering chemicals and guests ingesting them, there are two systems in place to help prevent this. First, there is the built in time slot for the staff to wipe off the tables after the TSA sprays, which will remove most of the excess chemicals and prevent ingestion. Additionally, we could lengthen the time the yellow light stays on so that the spray has more time to settle before anyone approaches the table.

  5. I can appreciate that you chose a very local and applicable problem to address.
    – Any plans to automate or eliminate the need for manually wiping down the tables?
    – What safeguards are in place should someone walk up and interrupt the process?
    – Any thoughts on an audible alert?

    • Thanks for your questions, Daniel!

      “Any plans to automate or eliminate the need for manually wiping down the tables?”

      We were unable to come up with a straightforward method of doing this, considering the liquid sanitizer must be removed from the table before the surface can be used. Short of a robotic apparatus straight out of The Jetsons, the only option would be to wait for the sanitizer to evaporate, which could potentially work based on the alcohol content of the solution. Many hand sanitizers with similar alcohol levels to surface cleaners have very short evaporation times (~15 seconds), so this would be something to experiment with and test the viability of.

      “What safeguards are in place should someone walk up and interrupt the process?”

      You’ll notice in the video that there are delays between the triggers for the light changes and the actual light change itself. This is to accommodate for situations where someone might pass the table and be in contact with the proximity sensor for a short amount of time. There is a delay set up where someone must trigger the proximity sensor for an extended period of time before the light changes color.

      “Any thoughts on an audible alert?”

      Many, actually! This was something we considered in the early phases of our design process, but ultimately decided against. The dining hall is noisy enough as-is, so an audible alert would have to be louder than the sounds of people talking and eating, which we imagine would prove to be highly obnoxious. Additionally, it would likely be confusing for staff to locate a table from an audio cue amidst the noise of the dining area. This could potentially work in quieter hours at the hall, but considering it would be most useful during the busiest hours when the noise levels are high, we do not think it’s a feature worth implementing.