Home Podcasts THMG175 – Shelter in Place Concepts, Part I

THMG175 – Shelter in Place Concepts, Part I


In this two-part series, we dissect the concepts for the seemingly constant struggle of, “Do I shelter in place or evacuate”. We break it down hazard by hazard, so sharpen those pencils.

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  1. What is sheltering in place
    1. The idea that people might be safer inside an area vs being outside to evacuate.
      1. Doesn’t mean to stay put. There are criteria that we will get into for safe areas
  2. Why do we shelter in place?
    1. There are a few reasons why shelter in place is necessary. Cost-benefit analyses.
      1. My parents are in Florida and last summer they got hit with a Cat 5. They decided to shelter in place. But they made a risk-benefit analysis. They live in a new homemade of concrete that was designed for a hurricane. They lost power but that was it. Had they lived in a stick style home their cost benefits analysis would have told them that they need to evacuate.
      2. While this is a really basic example the idea can still lend true to how we have hazmat tech would look to decide to shelter a population in place or to evacuate. The principle remains the same, the determining factors are just more.
      3. Sheltering in place is not just for hazmat. Please can opt to do this for a number of circumstances from natural disaster to man-made disaster to active shooter. We are just going to focus on some of the thoughts involved with Hazmat type sheltering in place.
  3. Type of emergency in which we shelter in place
    1. Bomb
      1. Type of harm
        1. Thermo (heat), mechanical from sharp metal, a pressure wave
      2. The reality of evacuation in some area
        1. ERG has ATF standoff distance
        2. Large cities cant always follow through
          1. So how do we know we are too close.
            1. Basic rule, if you can see it, it can see you, get something between you and the bomb, a building, a wall, a corner
      3. Things to consider when determining if a building is suitable
        1. Obviously, not all building will protect against bombs. Look at the Oklahoma City bombing, they were technique inside a building.
          1. So on that instance, if someone knew the bomb was there this is when we have to look at the size of the explosion and the building and be like, nope bomb to big, building to close let’s evacuate.
          2. But energy coming off an explosion actually is going to follow similar rules to distance as radiation. The pressure wave will diminish quickly.
          3. Building type and construction
          4. Windows.
      4. How to establish the safest inside environment
        1. Stay away from the window
        2. Stay away from exterior walls facing the blast.
      5. Information to population
        1. Usually, the area around is small, cell phone or having a representative shouldn’t be an issue.
    2. Chemical release
      1. Type of harm
        1. Inhalation is going to be our largest concern.
      2. The reality of evacuation in some area
        1. Again Large population areas can’t be evacuated
        2. Shelter in place might be faster
          1. Dr. Sohn from LBL stated, “A key take-home point in this sort of analysis is the plume passed over an individual point relatively quickly” (Personal Communication, Aug. 7, 2017). For the JRII Trials, this happened on the order of 5-10 minutes with a few profiles persisting to 20-30 minutes. He went on to say, “The time constant of most buildings (1 over the ventilation rate) is much longer which is why we get such a benefit from being inside something. With longer duration plumes the results will differ.” The interior concentrations were greatly influenced by the peak level of the plume which passed outside the structure. If the peak was high, there was a correspondingly high concentration inside which must be exhausted from the structure over time. Dr. Sohn explained that during the experiments the chlorine mixed evenly with the air inside the structures. This was typical of his experience with gas/vapor movement in other studies. He said, “Vapor density was less of a factor inside due to natural air mixing.” Dr. Sohn then addressed mitigation strategies, supported by the UVU Team, and recommended the following public actions during a release: 1) It is almost always better to stay inside than go outside. 2) Close exterior openings and stop ventilation systems when feasible. 3) Retreating to an interior room, without windows and away from exterior walls, provides a magnitude of protection. A closet is ideal because all of the fabric hanging has a higher sorption rate than a bathroom with tile and glass surfaces. 4) Stay inside until the outdoor concentration is lower than the inside concentration. There will come a time during the release when the concentration outside the structure or vehicle will be less than the concentration inside. Inside a structure or vehicle, the lower concentration will have a longer duration. Outside, the higher concentration will have a shorter duration. This relationship between duration and concentration is depicted in Figure 5. When will the time come that it’s safe to exit? It depends. “Wind is King” when considering when and if to move. High wind speeds outside, the absence of urban or natural barriers around the structure, and the number of environmental sorption surfaces will affect the duration of the high concentration around the structure. Also, see the discussion on the impact these variables have on plume duration.
      3. Things to consider when determining if a building is suitable
        1. The group of scientists, subject matter experts, and emergency response professionals that evaluated the Jack Rabbit data for this report all concur that the mitigation strategy pronounced in the past which included ‘duct tape seals and plastic’ would not be advised. An imminent plume passing over a structure while time is being spent retrieving the materials and applying the correct procedures resulting in limited effectiveness of the ‘seal’. The group felt that the mitigation strategies recommended by Dr. Sohn and endorsed by the UVU Team are more realistic and possibly more effective than previous strategies in the compressed time frame of an emergency incident.
  1. How to establish safest inside environment
    1. Turn of Hvac UNITS. This will minimize the amount of air flow
    2. Close windows and move people to a more interior space.
    3. Depending on chemical properties you might want to tell people to stay in the upper portions of the house
    4. Understanding the plume concentration curve will give you an idea that we need to be monitoring outside and inside. The moment level drop outside we need to vent because it will take along time for the chemical that are inside to come out.
  2. Information to population
    1. TV,
    2. Radio
    3. Loud speaker
    4. Cell phone
The Hazmat Guys

Author: The Hazmat Guys


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