1. How Shielding Works

Figure 5.1 is a diagram explaining how Shielding
 works in lay terms. Basically, an EMP or EMI
 (electromagnetic interference) source at the 
upper left (marked E and H field) strikes a barrier
 (usually metal) and reflects back to the left 
at the same opposite angle. The ratio of the 
incident electric or magnetic field to the 
corresponding reflected field is defined as 
the reflection loss (RLdB) measured in decibels.

A second loss, due to absorption (ALdB) of 
the wave traveling through the metal barrier, 
is shown inside the metal. Thus, Shielding
 Effectiveness, SEdB, is defined in Eq. (5.1)
 as a combination of both losses:

 SEdB = RLdB + ALdB                   (1)

For more details, see the author's handbook on “Grounding and Shield-ing, published by Interference Control Technology.


EMP Protecting Buildings 
via Shielding, Bonding, Grounding, Surge Suppression & Filtering
 1: How Shielding Works
 2: Shielded Buildings, Rooms and Cabinets
 3: Shielding of the Building Facade
 4: Grounding the Shielded Building.
 5: Shielded Windows, Doors & Other Leakages
 6: Shielded Wires and Cable Entries
 7: Filters and Surge Suppressors.
 8: Testing Shielded Building Performance
 9: Maintenance Considerations
Article Summary 

This article shows how to provide EMP protection to an entire building, first without solar rooftop addition which is covered in another article. Remember if the building cannot be protected against EMP, per se, then any other additives are academic since most/all the building's electrical/electronic contents have burned out as discussed elsewhere on this website. On the other hand, if the building is EMP protected and there exists no solar or other energy backup, the building survival is almost meaningless as there is no electricity either.

the amount and kind of EMP protection needed for an entire building before solar-PV is added is discussed here. This article illustrates how this protection may be achieved at the component level along with different options for EMP hardening solutions. It further shows that aging effects, such as in building grounding components and earthing, can significantly time compromise EMP protection and how this can be mitigated.

In EMP protecting of the entire building, it is readily observed that all outside windows and doors need special shielding treatment. All cable entries must have surge suppressors and possibly filters. The outer shield of entrance cables must be bonded to the building shield and earth grounded to keep the radiated EMP from flowing onto the building shield where compromise otherwise develops. Even the earthing ground (sand or loom soil, wet or drought) significantly impact the shielding performance of the building facade.

The remaining sections address testing to confirm the achievement of the needed 80-dB shielding (below 64 MHz) and maintenance required as the building and its grounding age, together with some measures of cost.

The presentation is mostly made in a light technical manner so that nearly all readers can follow. Supporting graphics will especially help. However, some marked sections can be skipped by the lay reader as they become somewhat detailed.
5.2 Shielded Building, Rooms and Cabinets (other than the first paragraph, the lay reader can skip this section)

2. Shielded Building, Rooms and Cabinets


Figure 5.2 (at the right) and Eq.(5.1) (above) illustrate
 that there exists three  possible levels of shielding. 
The benefit of shielding the  entire building to 80 dB 
(or designated lower number) means that nothing else
 inside  needs to be shielded. Thus, existing cell phones,
iphones, laptop computers, peripherals, climate controls,
and all the rest of electrical and electronic devices inside
can continue to be used. However, shielding  a building 
to 80 dB in some cases may become expensive (e.g:
possibly more than 10% of the entire building cost by 
2014; lower percentage later).

Consequently, one or more internal shielded rooms 
could be added where the more sensitive items would
be located, and the entire building shielding can be
correspondingly reduced. For example, suppose a cheap
aluminum foil or sprayed copper paint on the walls, ceiling and floor (bonded and secured) is used for the inside building conductive skin to reduce its requirements to, say, 40 dB. This may appear to drop the price of the building shielding. But, be aware that the electrical wiring in the outside walls are still not protected; therefore, this will not work.

However, if the items in the proposed internal shielded enclosure have a radiated susceptibility below 10 V/m (the assumed conditions per RS-105 of MIL-STD-464), the additional shielding can be achieved in an internal screen room or cabinet or box size, as applicable. Shielded enclosures of the quality offered by the EMC manufacturers are shielded to about 120 dB and represent a huge overkill and, therefore, would not be used here.

The shielded building skin is best placed on the outside with sheet metal building walls bonded where joined and each of the six sides of the building (roof, basement floor, and four sides) is bonded along its entire length Do not try to shield the wall board on the inside as this will not work as stated above because all the wiring trapped between the inside and outside skin will act as a gigantic pick antenna and destroy the shielding performance.
5.3 Shielding of the Building Facade

How to shield the building facade (outer skin)? What constitutes the basic material under the building skin or envelope, such as with vinyl siding? In USA, it is typically a plywood lath sheathing in the North and concrete blocks, stuccoed over, for residential in the South. For commercial it may be aluminum composite panels, copper or stainless steel sheets, weather-board, etc. These and other materials are dependent on whether or not the building already exists or has not yet been designed or built. Most specifics of this discussion are beyond the scope of this article and involve important architectural matters.

Another article spoke of BI-PV (third generation materials = building integrated, photovoltaics) and involve the simultaneous decision of combining solar BI-PV additive which also becomes the building facade. Of course, this is best done for a new building. However, BI-PV would have to be shielded. 

If the facade of the existing building permits the direct 
addition of an aluminum foil, then the household, 1 mil
 (= 0.001 inches = 0.0254 mm) or a more ruggedized 
version (e.g., 3 mils) provides all the shielding needed.
 For example, our shielding effectiveness computer
 program #330A provides the following shielding 
performance for 1 mil aluminum foil shown in the 
graphic to the right..

One mil of aluminum foil provides 96 dB of shielding.
 From Chap 3, 80 dB was determined to be the required
 amount of building skin shielding to protect against 
a EMP incident for most applications. So there exists
 sufficient shielding. But, how are sheets of foil to be
 bonded to their mounting material siding and how are 
they mated together at their edges

Basically, an adhesive spray is made on the mounting material back and the foil is placed thereon. A squeegee may be used to smooth the mounting. However, the foil overlap should approximate one inch (2.5 cm), and a masking tape used to secure the overlap junction. Do not spray the foil adhesive in the 2.5 cm region as metal must be bonded to metal without any other material in between to ensure a high conductivity.

The foil must end at each window sill or outside door sill or frame as the window/door will receive its own shielding. An electrical bonding agent or gasket (described below) is used to electrically connect the building facade with each window and door periphery. 

To demonstrate the need for meticulous workmanship, sup-pose that a hole in the shield foil as small as 0.1 inch (2.54 mm) resulted. What is the new shielding performance of the foil with the hole? Fig 5.5 shows the resulting performance of 58 dB at 64 MHz – the frequency of the second node in the HEMP time-domain pulse discussed earlier in Section 3.4. This hole can be developed in many ways. One way: suppose a workman secured the foil with a screw into a plywood siding (accidentally or intentionally); then he removed the screw for whatever reason! This explains why two layers of foil were used earlier and two layers of wire mesh screen are used on windows and solar panels. 

One possible option to the above foil is to use copper or aluminum paint, applied by brush, roller or spray. One source (LessEMF.com) reveals a copper latex paint reported to produce less than 0.1 ohm/square (shielding effectiveness of >72 dB below 1 GHz) for 2 mil deposit. Five mil in two coats will produce the required 80 dB at a paint cost of roughly $2/sq ft ($21/sq.m). Exclusive of windows, doors and other building skin discontinuities, a 20,000 sq. ft building will cost $80k in conductive paint (Ed: possibly reduced to ≈ $25k for quantity of over 200 gallons).

A finishing non-conductive protection coat of latex paint is applied. One major benefit of the paint approach is the relatively easy application by spraying and the avoidance of foil overlaps, and electrical gaskets except at windows, doors, etc. described below.

Duralux Aluminum Marine Boat Paint Green, or equivalent may be a viable protection at a significantly lower cost per gallon ($85). In all cases the surfaces must be clean free of dust, dirt, oxides, etc. Sand blasting may be a necessary first step. Application to new buildings is less expensive than retrofits to existing buildings.


To Be Continued
EMP Building Material being transfered here