Anatomy of a Safe Cell

The Anatomy of a Safe Cell:

Features, construction methods, and performance
of the most advanced NBC air filter available

Fabricated by: American Saferoom

 

The Safe Cell and its accessories are all designed to fit and function together. By viewing your entire protected space as a single system, we have eliminated the guesswork in constructing a shelter air filtration system.

Features

Integrated overpressure
Unlike room air filters with an adapter kit added to draw air in from another room, the Safe Cell was designed from the start to draw air in from an adjacent space and overpressure your protected space. This is the same principal used in every military and government protected spaces - from armored vehicles up to massive bomb shelters. Because all air is flowing outward from your protected space, this overpressure denies access to airborne toxins, isolating you from the toxic environment.

Instant isolation room
All Safe Cell models can be configured to create a CDC grade isolation room. All you have to do is to remove the air intake hose and place it on the air output port. The Safe Cell will then draw air from the protected space and expel it outside - creating a negative pressure in the room and filtering the air before it is discharged. If you have an person that develops a communicable disease in your home, you can bring them into your protected space and isolate their droplet nuclei (airborne body fluids) from the rest of your family.

   
Pusher mode
The Safe Cell can be easily configured to be in an adjacent room - such as a closet - and "push" the filtered air into your protected space.
   
Mobile applications
The Safe Cell has been installed in cars, trucks, heavy equipment, mobile command shelters, and decontamination tents. It can also be installed in recreational vehicles, boats, and aircraft. All models feature marine grade blowers and corrosion resistant construction.
   
Backup systems
The Safe Cell features redundant backup systems - most models have an automatic switching power supply that trickle charges a user-supplied battery and then draws from it in the event of a power outage. All Safe Cells are ready to instantly receive the hand pump. You can literally hold you breath while you slip on the hand pump and start pumping.
   

Easy installation
Due to its modular design, installing the Safe Cell in your protected space can be completed with simple hand tools in about an hour.

The wall mount bracket is designed to mount to studs in typical residential construction on 16 inch centers. When your NBC filter is mounted on the wall, it cannot be tipped over, moved, or misplaced. The Safe Cell attaches to the wall mount bracket with quick release fasteners - that require no tools to remove it. With our automotive vent kit and a second wall mount bracket installed in your vehicle, you can take your protection with you if you have to evacuate.

All of the hose connections are slip-fit. That means you simply push them onto the connection with a slight twisting motion.

Every Safe Cell comes with a comprehensive installation and operation manual showing exactly how to install it.


   

Easy operation
Plug it in and turn it on: the Safe Cells with battery backup have separate switches for the power supply and the blower. The single voltage Safe Cells have only one power switch that turns the blower on and off.

Because you may be in a hurry and stressed when you need to operate it, the Safe Cell features easy-to-read placards at every point that you interact with it. Operation is easy and intuitive even without the manual.

   

Foolproof
Every Safe Cell has a single speed blower. Once it is installed and tested in the protected space, you are either protected or not, and when the user can lower the blower output with a variable speed blower, it is possible to have the Safe Cell on, but putting out enough air to create an overpressure.

These blowers are all marine grade - which means that they are designed to resist corrosion in the harshest environment.

Construction Methods

Built like a hydraulic cylinder
The top and bottom end bells on the Safe Cell capture the HEPA filter and the carbon adsorber in the same way that the end plates capture the tube in a hydraulic cylinder. This capture method ensures that the pressure applied to the seals on the filters is equalized around their perimeter. In other words, this construction method prevents the seals from being over tightened on one side and loose on the other - loose seals leak dirty air.

 

The best filters available
In any filtration system, you want to go from progressively large to small particles being filtered. The Safe Cell features a bank of three filters: the pre-filters, the HEPA filter, and the war gas carbon adsorber. These filters are easily replaceable.

All of our filters are made to our specifications by three different companies in the United States. We chose the best specialized manufacturers for each of our three filter banks. The gaskets on the HEPA filter and the carbon adsorber are rabbited (puzzle cut) to prevent air leaks.

   
The pre-filters have both a gross and a fine media. They allow you to replace the relatively inexpensive pre-filters and it keep the HEPA filter from becoming clogged with large particles and adding resistance to the system.
   
The HEPA filter we have made for us is beyond what is commonly marketed as a "true HEPA" which can be nothing more than pleated paper media. HEPA is an acronym for High Efficiency Particulate Air filter. Its function is to trap the smallest particles possible. Our HEPA filters are individually tested with a DOP test to MIL STD 282-1995. This has been the industry standard test method for many years. It is conducted using a forward light scattering photometer. The HEPA is challenged with 0.3 micrometer particles of dioctylphthalate (DOP). By measuring the upstream and downstream concentration of these particles, the HEPA filter efficiency can be calculated. Our HEPA filters also have been awarded Underwriters Laboratories Classification - UL 586. This classification is to insure that each HEPA filter cell is individually tested at the factory. Additionally, representative HEPA filter cells are tested by UL to ensure that they provide their rated HEPA level filtration, after being subjected to the following conditions of a high moisture environment of (90% R.H.), a high temperature environment of (371 deg/C), low temperature environment of (-3 deg/C). UL also subjects the HEPA filter cell to a spot flame test of (954 deg/C).
   
The nuclear grade war gas adsorber is a block sieve adsorption filter cell consisting of two containment media's and a center block of a granule nuclear grade war gas carbon blend - NUK-TK TEDA and ASZM-TEDA. This special blend of two kinds of activated carbon adsorbs warfare gases and radioactive iodine in order to meet the requirements of US Army Corps of Engineers ETL 1110-3-498 standard for war gas removal.
   
Power Supply
The Safe Cell models that feature the automatic battery backup system have a custom designed and built power supply in them. This power supply is a box that mounts inside the top end bell and regulates when and where the power comes from. There are two power cords on these models - one for 110 volt to 220 volt AC and one for 12 volt DC. The power supply automatically trickle charges a user supplied battery connected to the 12 volt DC power cord. This means that it continually checks the battery's charge and when it drops, it will recharge it automatically. When the AC power (from an electrical outlet) is interrupted (a power outage), the power supply automatically switches to drawing from the battery. A normal automotive or marine battery will last from 16 to 24 hours - at full charge. This gives you peace of mind when you go to sleep knowing that if the power fails, your NBC filter will continue to maintain overpressure.
   

Wall Mount Bracket
There is a good reason that smoke alarms, fire extinguishers, and some first aid kits come with wall mounting kits - when you need life saving devices, you want to know where they are at.

The Safe Cell wall mount bracket is laser cut stainless steel with fabricated L-brackets that attach to the spacers between the end bells.

The L-brackets are attached to the wall bracket with star nuts that can be unscrewed by hand - you can immediately remove the Safe Cell from the wall if you need to move it to another room or a vehicle.

 

Performance

There are air filter manufacturers that have post the rated blower capacity and claim that it is the true system airflow. This is a disingenuous attempt at deceiving the customer. All blowers come with an airflow rating - for that blower alone. But that does not include the resistance to air movement before and after the blower. There are two types of resistance to airflow in a filtration system: internal resistance from the filter media and internal ducting, and external resistance: the size, and shape of the protected space plus the ducting to and from the protected space. The internal resistance is a factor of the engineering that is utilized in the design and construction of the air filtration unit. The external resistance is determined by a variety of variables - some of which are: protected space location, filter unit location, air exit location, and "baffles" that slow down the air exchange process like storage items and people inside the protected space, and the internal size and obstructions inside the hoses and pipes that deliver and exit air.

The most common way to measure the efficiency of the entire system of the protected space is air exchanges per hour. As an example, if you have a 10 by 10 foot protected space with an 8 foot ceiling, you have 800 cubic feet of volume to protect. The measurement of air exchanges per hour is how many times per hour that 800 cubic feet of safe, breathable air is blown into and out of the protected space.The most stringent protected areas are in hospital isolation rooms that have patients in them that are highly infectious. The CDC recommends between 6 and 12 air exchanges per hour for a hospital grade isolation room. This is partially because the patient and the support personnel are converting oxygen to carbon dioxide by breathing and it needs to be removed from the protected space. The other main reason is the droplet nuclei (airborne body fluids or bio aerosols) from the infectious patient must not be allowed to accumulate in the isolation room - accumulating in the filter media is a much better place than your lungs or on surfaces in the room. You can change the filters at certain, pre-scheduled intervals. The other factors are humidity and heat accumulation - body heat and moisture laden exhaled air can have a significant impact on the comfort and safety of people in the protected space.