Tag Archives for " co2 levels "

How do emergency shelters get fresh air?

If you must go into an emergency shelter, then you can bet that conditions outside are not good, whether it’s a natural disaster, war or safety from criminal activity. You can store many supplies such as food and water for staying in a shelter, but without clean air, survival will only be minutes instead of days, weeks or months!  There are a number of things that air and ventilation systems need to accomplish for shelters:

1. Providing a positive pressure at all times so that contaminated air from leaks or outside sources does not enter the shelter.

2. Filtering out contaminants such as nuclear, biological, chemical (NBC) or smoke toxins. 

3. When the shelter must be completely closed up due to bad air quality outside, two things must happen: 

1. Removing carbon dioxide (CO2) byproducts of the people residing in the shelter.

2. Providing supplemental oxygen to replace the oxygen depleted by residents

Let’s go through these in order.  When the shelter is not being used or only tested during good external conditions, then its ventilation system can operate like your home system: bring in outside air, send it through filter(s) to remove dust and normal microbes like mold and bacteria, and keep a slight “overpressure” of 0.3 inches of water so that leaks in the shelter’s walls and doors will only cause air to move out, never in.  The exhaust “vents” are really one-way valves that only let air go out, so that air coming in is controlled.  They also protect residents of the shelter from any explosive “blast” of pressure and debris.  For this reason, they are called overpressure blast valves.   

The flow of fresh air should be similar to what is required at home: according to US standards, that is 0.35 air changes per hour (ACH) or 5 cubic feet per minute per person, whichever is greater (5 cfm is the specified minimum required by the US military, whereas 15 cfm is the recommended supply for ventilation in residential and commercial buildings).  That said, 5 cfm is usually the design criteria to remove the moisture and carbon dioxide (CO2) that shelter residents exhale, and make them feel comfortable.  The air intake must be protected from water and animal intrusion and sufficiently distant from the exhaust (overpressure blast valve) so that used air is not recycled through the shelter.  Routing airflow through the shelter ensures that the exhaust is in the airlock (the chamber where residents enter and exit) so that any outdoor contamination is flushed out with the positive air pressure.

NBC filtration (or as the military defines it CBRN: Chemical, Biological, Radiological, and Nuclear) requires unique filter material.  Pre-filters are used to keep dust and particulates out of the airstream, and then activated carbon impregnated with specific minerals is used to adsorb gasses that may be emitted during disasters or wars.  For example, the activated carbon may be mixed or “doped” with potassium permanganate, potassium iodide, or magnesium dioxide or copper dioxide (see our article on what these materials remove from air). These are not typical systems used in home ventilation, as the activated carbon must be in sufficient purity and quantity to allow filtration for a number of days until outside air clears.

In the event that outside air is heavily contaminated, the ventilation system will need to be completely sealed off and the shelter will operate more like a submarine, where supplemental oxygen is added and CO2 is removed.  The atmosphere needs to be maintained close to ambient outdoor air, at 19.5% oxygen and less than 0.2% (2000 ppb) CO2, and that’s a complex task when humans are using oxygen and expelling CO2 every minute!  It’s good in this case to use the same two principals we introduced in our article on submarines: use good instruments to measure the air quality and have redundant systems to ensure that each function is maintained in case of system failure.  In well-planned shelters, it’s common to have the following instruments: thermometer, humidity meter, differential pressure gauge (to maintain 0.3” water overpressure), smoke alarm, low oxygen detector, carbon monoxide alarm, carbon dioxide alarm, and a radon meter. (NBC Air Filtration Systems)

Although NBC filtration systems can be expensive, systems for adding oxygen and removing CO2 are even more expensive and complex.  Here are some ways that military and professional systems do it (Air Supply Principles in Isolated Shelters & Chambers):

Supplemental Oxygen is available in three different methods:  

1. Oxygen can be stored in a gas form under pressure or as liquid oxygen in cylinders, and released from these tanks when needed.

2. Oxygen generators can separate oxygen from compressed air stored in the tanks, or even generate oxygen from electrolysis of water (passing an electric current through it).

3. Oxygen “candles”, also called chlorate candles, are a very hot-burning cylindrical candle that actually puts out oxygen instead of consuming it.  

Removal of CO2 requires even more chemistry. On average, each person produces 1 kg of CO2 per day, and buildup of CO2 in the air is lethal (see our article on CO2 levels).  Therefore one or more of the following systems is needed:

1. CO2 scrubbers use a soda lime or lithium hydroxide material to remove CO2 from the airstream, but they produce a lot of moisture and heat and require space for storage of filters and material, which could be prohibitive for smaller bunkers.

2. Regenerative carbon-dioxide removal systems use a solid amine material and are advantageous in terms of space required, but have a high energy consumption and are costly to install.  

Since air supply is one of, if not the most, critical aspects of a shelter, these systems are best designed and installed by professionals who have experience.  In the survival shelter industry, NBC filter systems made by Israeli and European (Finnish and Swiss) companies differ significantly from those made in the US and UK.  The former systems are more robust, with significantly better materials, engineering and more generous carbon supply than others.  (NBC Air Filtration Systems)

Due to threats of war, disease and scarcity, many people are becoming interested in emergency shelters, but an improperly designed or constructed shelter can be more life-threatening than life-saving!  If you are interested in building or buying an emergency shelter, we recommend you check out this article and research first.  Having a place to retreat in emergency requires a lot of forethought and planning to truly make it "safe"!

Less Coffee, More Fresh Air!

At some point in most peoples’ lives, fatigue is a fact of daily life.  We can chalk it up to too much work and not enough sleep, or poor quality sleep, or a virus that seems to be “going around”.  But what if it could be as simple as not enough fresh air?  Simple…yet sometimes not easy to fix, when opening the windows lets in more harmful air than good.  Let’s dig into this “simple” cause…

Different regulations regarding ventilation have been around for a long time, way longer than the American Society for Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) published its first Standard 62 for ventilation. The first, ANSI/ASHRAE Standard 62-1973, Standards for Natural and Mechanical Ventilation, presented minimum and recommended ventilation rates for 266 applications and became the basis for most state codes.(ASHRAE.org)

This standard has been revised several times since 1973, and the current standard calls for homes to “receive 0.35 air changes per hour  but not less than 15 cubic feet of air per minute (cfm) per person.” (epa.gov)  Why?  According to Britannica.com, Clean, dry air consists primarily of nitrogen and oxygen—78 percent and 21 percent respectively, by volume. Without any other contaminants such as carbon monoxide (from combustion) or radon (from the earth) entering a building, humans change the composition because we take in oxygen and breathe out carbon dioxide.  Our lungs can still rebreathe this air “safely” until it decreases below 19.5% (OSHA threshold for oxygen in atmosphere), but increaseing levels of carbon dioxide (CO2) may cause occupants to grow drowsy, get headaches, or function at lower activity levels.  (healthybuildingscience.com)  What’s the threshold of CO2?  

• NIOSH (National Institute for Occupational Safety and Health): 1,000 ppm (parts per million in air) are a marker suggesting inadequate ventilation.  

• ASHRAE recommends that carbon dioxide levels not exceed 700 ppm above outdoor ambient levels.   (Normal range for outdoor levels are typically in the 350-450 ppm range). 

• OSHA (the Occupational Safety and Health Administration) limits carbon dioxide concentration in the workplace to 5,000 ppm for prolonged periods, and 35,000 ppm for 15 minutes.  

Taking the most conservative route, 1000 ppm is only 0.1%.  Wow, it doesn’t take a lot of CO2 to make stale air!  If this is the gold standard, why are we suffering in stale air?   The answer is that  many places in the US do not require building permits in order to build or renovate a home.  For this reason, it’s up to the homeowner to know what is needed and make sure it’s installed.  If the HVAC technician does not design fresh air into the system, and the homeowner does not know about the need for it, the home won’t have it and the air will be stale.  Case in point: my 1982 home in the country.  It cools, heats, and circulates stale air.  

Take this tweet from Andrej Karpathy and Elon Musk, who know a bit about technology: 

And then the public chimed in: a Stanford professor used to take CO2 measurements in a lecture hall before packing 100+ students in for 1.5 hours, because some halls did not have enough ventilation to sustain deep thought!  Then a restaurant worker began to think, oh, so that’s maybe why I got dizzy sometimes during peak hours of a restaurant?  And another: his son used to wake up crying but since increasing ventilation in his room, the child sleeps a lot more peacefully.  

So if you want to measure your air, lethargy, unclear thinking and headaches don’t have to be part of your day!  There are lots of CO2 monitors on the market, with most starting about $65-70.   This monitor by INKBIRDPLUS shows temperature, humidity and CO2, and also allows you to customize an alarm for different levels of CO2 (they recommend normal (400-700 ppm), warning (700-1500 ppm), and dangerous (1500-5000 ppm)).  

Can you imagine measuring the CO2 while sitting in a conference room or in a lecture hall?  With such technology at your fingertips, there’s no reason to be ashamed to say “I need a break”.   Your brain and body will thank you!