Shelter-in-Place Calculator

Understanding Shelter-in-Place

Shelter-in-place is the emergency protocol of staying indoors and sealing your space from outside air contamination. Unlike evacuation, which moves you away from danger, sheltering in place protects you by keeping dangerous substances out of your breathing space.

This protocol is used during:

• Chemical spills: Industrial accidents, train derailments with hazardous cargo
• Hazmat incidents: Toxic gas releases, chemical plant accidents
• Nuclear emergencies: Radioactive material release, nuclear plant incidents
• Severe air quality events: Wildfire smoke, volcanic ash
• Biological threats: Airborne pathogen release

According to FEMA, shelter-in-place can reduce exposure to airborne hazards by 80-90% when done correctly. The key is speed—you need supplies ready to deploy in minutes, not hours.

Choosing Your Safe Room

Ideal Safe Room Characteristics

Not every room works equally well for shelter-in-place. The ideal room has:

• Interior location: Away from exterior walls when possible
• Upper floor: Many hazardous chemicals are heavier than air and sink
• Few windows: Less sealing required, fewer gaps
• Water access: Attached bathroom or water supply inside
• Adequate space: ~10 sq ft per person minimum
• Phone/communication: Cell signal or landline access

Room Comparison

Essential Shelter-in-Place Supplies

Sealing Materials

Plastic Sheeting

Plastic sheeting creates the air barrier that keeps contaminated air out. Key specifications:

• Thickness: 4-6 mil (6 mil preferred for durability)
• Material: Polyethylene (standard hardware store variety)
• Coverage: Cut pieces 6 inches larger than openings on all sides
• Quantity: Cover all windows, doors, and vents with overlap

Duct Tape

Standard duct tape works well for sealing plastic to walls. Requirements:

• Width: 2-inch standard width
• Quality: Name brand for better adhesion
• Quantity: One roll (60 yards) per room minimum
• Storage: Keep at room temperature (adhesive degrades in heat/cold)

Pro tip: Label each pre-cut plastic sheet with its destination (e.g., "Bedroom Window 1") and include the matching tape strips pre-torn.

Air Filtration

Even in a sealed room, some air exchange occurs. Additional filtration helps:

• HEPA air purifier: Filters particulates including many chemical particles
• N95/N100 respirators: Personal protection if seal fails
• Wet towels: Place under doors for additional sealing
• Plastic bags: Cover outlets and small gaps

Emergency Supplies

Your sealed room needs to sustain your household for the duration:

Water

• 1 gallon per person per day
• For 4-hour shelter: 1-2 quarts per person minimum
• Store in safe room or adjacent bathroom

Food

• Non-perishable, ready-to-eat snacks
• No cooking required (stove vents outside)
• Granola bars, crackers, dried fruit, nuts

Communication

• Battery or hand-crank radio (NOAA weather)
• Cell phone with charger
• Written emergency contact list

Comfort & Safety

• Flashlight with batteries
• First aid kit
• Medications (regular and emergency)
• Entertainment for children
• Pet supplies if applicable
• Bucket with lid (emergency toilet)

Step-by-Step Sealing Process

When Shelter-in-Place is Ordered

1. Get everyone inside immediately—including pets
2. Turn off HVAC system—prevents drawing outside air in
3. Close all windows and doors—start with exterior, then interior
4. Close fireplace dampers—seal any chimney access
5. Go to your safe room—bring supplies if not pre-staged
6. Seal the room in this order:
   1. Door(s) - plastic sheet, tape all edges, wet towel at bottom
   2. Windows - plastic sheet with 6" overlap, tape all edges
   3. Vents - cover HVAC supply and return vents
   4. Outlets - optional but provides additional protection
   5. Any gaps - caulk or tape visible gaps in walls/floor
7. Monitor emergency broadcasts—radio or phone alerts
8. Wait for all-clear—do not unseal until authorities advise

Sealing Windows

Windows are typically the largest openings and highest priority:

1. Unroll pre-cut plastic sheet sized for window + 12" total (6" overlap each side)
2. Position top edge 6" above window frame
3. Tape top edge completely first—smooth, no gaps
4. Pull plastic taut and tape side edges
5. Tape bottom edge last, ensuring contact with wall
6. Run finger along all tape to ensure adhesion

Sealing Doors

Doors have more gaps than windows—seal carefully:

1. Close door firmly
2. Place wet towel tightly against bottom gap
3. Cover entire door and frame with plastic sheet
4. Tape top and sides completely
5. Tape bottom, overlapping onto floor if possible
6. Do NOT seal from the outside—you need to exit eventually

Sealing Vents

HVAC vents can draw contaminated air even when the system is off:

1. Turn off HVAC system at thermostat before sealing
2. Cut plastic 4" larger than vent on all sides
3. Tape all four edges securely
4. Don't forget return air vents (often larger, near floor)

Duration and Air Quality

How Long Can You Shelter?

The limiting factor in a sealed room isn't air tightness—it's oxygen consumption. A completely sealed room will eventually develop elevated CO2 levels:

• 1-2 hours: Safe for any reasonably-sized room
• 2-4 hours: Safe for most prepared rooms
• 4-8 hours: May need larger room or slight ventilation
• 8+ hours: Consider controlled ventilation with filtration

Reality check: Most chemical emergencies requiring shelter-in-place resolve within 2-4 hours. The hazardous plume passes, and authorities issue an all-clear.

Signs of Poor Air Quality

• Headache
• Dizziness
• Difficulty breathing
• Unusual drowsiness

If you experience these symptoms and cannot unseal safely, crack a single opening and apply a wet cloth as a filter.

After Shelter-in-Place

When to Unseal

Wait for official all-clear from authorities. Do not assume danger has passed because:

• Chemical plumes can shift with wind changes
• Heavier-than-air substances may linger at ground level
• Emergency responders need time to verify air safety

Unsealing Process

1. Wait for official all-clear announcement
2. Open windows and doors to ventilate
3. Turn HVAC to fan-only mode to circulate fresh air
4. Leave the building briefly if possible while it airs out
5. Remove and properly dispose of plastic and tape
6. Restock your shelter-in-place kit

Special Considerations

Apartment Dwellers

Apartments present unique challenges:

• Shared HVAC: Your system connects to others—seal vents carefully
• Limited room choice: Use bedroom with attached bath if possible
• Interior units: Often better positioned than corner units
• Building alerts: Follow property management guidance

Those with Medical Needs

• Ensure oxygen concentrators/tanks are in safe room
• Keep nebulizers and respiratory medications accessible
• Have backup power for medical equipment
• Consider medical-grade respirators for protection

Families with Young Children

• Prepare activities and comfort items in advance
• Practice the sealing process as a drill
• Explain what's happening in age-appropriate terms
• Diapers and infant supplies must be pre-staged

Preparation and Practice

Creating Your Kit

1. Measure all openings in your safe room
2. Pre-cut plastic sheets with 6" overlap on all sides
3. Label each sheet with its destination
4. Store supplies in the safe room or immediately adjacent
5. Include instructions for any household member to follow

Practice Drills

Run through the process at least once per year:

• Time yourself sealing the room
• Identify areas where you hesitated or struggled
• Ensure all family members know the process
• Check supplies for degradation (tape adhesion, plastic condition)
• Update supplies as needed