By Harry Zackrison, P.E., CVS, FIES  

The present trend in TEMPEST protection is to seek the most cost effective route in reducing one’s risk to tolerable levels. In the past, the way to achieve these levels was using the commercial Radio Frequency (RF) shielded enclosure.

With the tremendous increase in electronic equipment in secure government facilities structures that cause electromagnetic interference it has become an increasingly serious problem. The commercial efforts to solve the interference problems also work to solve TEMPEST problems such as acoustical attenuation. RF jamming decreases the strength of electromagnetic radiation and interception along with the inclusion of protecting against electronic surveillance.

There has been an ongoing investigation to explore alternative ways to achieve RF protection. In many instances, the solutions to the interference problem can be adapted. Such products as conductive paints, tapes, fabrics and building materials have been designed and put into production. In most instances, a standard shielded enclosure with 100-dB attenuation may be excessive in protection and cost, while a less expensive alternative shielding approach can provide the required RF protection. The following data covers some of the shielding processes that have been investigated and found to provide sufficient levels of attenuation to electromagnetic radiation.


The basic concept behind shielding is to find a material that is effective in decreasing the strength of electromagnetic radiation.  When one has found the appropriate material, it is then important to form a “closed box” using this material.

Each piece of this material must be joined together in such a way as to prevent leakage areas where radiation can exit or enter.  Where openings are necessary, such as in doors, windows, air vents, etc., proper shielding techniques must be employed so that the shield’s integrity is maintained.

Individual Room Shielding 

Plywood sheet boards 0.75-in to 1-in thick, coated with lead, a sheet copper stock of 3-oz copper Sisalkraft of aluminum sheeting epoxy cemented or attached to it for use as a perimeter shielding medium is a cost-effective approach.  This type of design approach uses a copper aluminum or lead covered sandwiched plywood wall, floor and ceiling construction technique.  Both wallboard sides, top, bottom and sides are covered with a continuous and overlapping metalized sheet.  These coated 0.75-in thick plywood boards are joined at the corners, mid points, top and bottom with overlapping metal clamps. The corner walls are tied together, and RF sealed with a continuous shielding corner seal cap.  Continuous walls where they butt together in a seam, are attached and sealed by a continuous shielding wall seam seal cap.  This method of SCIF design can produce 70-dB of RF and EMP attenuation.  This technique has been in use for the past 40 years but has been superseded by even more advanced techniques in the last 25 or 30 years.

Metalized paint conductive coatings can be rolled on or sprayed on walls, floors and ceilings will produce up to 50-dB of attenuation levels of RF and EMP protection.  Sheet copper stock Sisalkraft applied to walls, floor and ceiling can produce 70-dB of RF and EMP attenuation. The copper foil is attached directly to the gypsum board (drywall or sheetrock).  The copper foil is also attached directly to the concrete floor and has either a carpet on it for protection or preferably 0.5-in to 0.75-in thick plywood is applied over the foil, with a separate rug or carpet over it.  This design approach can produce up to 70-dB of RF and EMP attenuation, the same as the copper, aluminum or lead covered sandwiched plywood construction method.

Metal pan construction utilizing RF filter gaskets between sections of metal pans bolted together can produce 110-dB of attenuation. A 3/8-in thick welded seam, steel plate construction can produce a maximum of 120-dB of RF and EMP attenuation. This type of construction method is more obvious to outsiders as to what you are doing, the attenuation levels to which you wish to attain, and why.  With all the above methods of design and construction, acoustical attenuation must be dealt with and designed in. This requires steel or wood studs, offset mounted away from the SCIF walls.  Gypsum board 3/8-in thick is applied to these steel or wood studs with dry wall screws and a sound attenuation acoustical batt is applied between this sheetrock and SCIF wall.  A special note must be taken in that the steel or wood stud must not contact the SCIF wall, as acoustical energy (sound) can then be directly transmitted to and through the SCIF wall.

If a SCIF is placed adjacent to a perimeter wall having fenestration, a standard approach is to use a wire mesh screen making metal contact between copper mesh and metal screen trim frame to metal copper Sisalkraft stock wall is required to attenuate RF, EMP, and dB levels.  Silver and gold deposit on a film placed on the interior or inside of the glass window is another excellent solution.  An alternative to screen materials is a conductive translucent plastic material built into a thermal pane window. One exclusive manufacturer says it can produce upwards of 50-dB window from 10-Mz to 1-GHZ, which has been difficult to confirm in field tests.  Screen laminated windows are still another approach in obtaining the above desired results. In addition, white background sound should be generated to mask out intelligible speech.  Sound impinging on the glass window is converted to infrared (IR) heat which can be picked up with an IR scanner and can then be reconverted back into intelligible sound or speech by a deciphering device.

An IR scan of a facility’s glass fenestration can pick up the IR converted acoustical sound such as speech and noise and can translate it back into intelligible voice.  But of equal interest and importance is that a remote over the top laser can pick up speech from the glass and in many cases from miles away.  Armed with UUNETS’ map net or Map Quest you can insert your address and zip code (pick up receiving point) and their address and zip code.  Both locations will be appropriately starred on the map.  Next you will need the exact elevation above sea level for both locations followed by the exact elevations of the building you are targeting and the elevations of the tallest buildings in the way, between you and them.

Total Building Shielding

In the last 10 or so years another shielding technique that has been employed successfully is the concept of either shielding an entire building or at least the area behind the Hard Line and the Annex during the construction phase. The approach is to spend extra money during the construction process for a lightweight shielding material that can be applied either on the face of the building or interior of the exterior wall that can provide considerable attenuation. This should eliminate the need for many individual shielded rooms and TEMPEST suppressed equipment.  The purchase of less costly “off the shell” equipment, combined with the elimination of many individual shielded enclosures can add up to overall cost-savings.  The RF design goal is to achieve 60-dB of RF Electric/plane wave attenuation from 10-MHz to 450-MHz which is difficult to do, as well as tough to meet and hard to prove.


It is not believed that the standard PVC coupling as detailed that is the most commonly used will ever work properly, if at all, in any TEMPEST, SCIF, EMP, NEMP or HEMP facility.  This detail indicates that the incoming ferrous pipe should penetrate the perimeter wall and then should stop immediately inside of the exterior perimeter wall. There are ways that the detrimental aspects of using the PVC penetration/PVC break can be alleviated. The electrical overcurrent device cannot function properly due to an induced torrid choke effect. It will not see a bolted ground fault or even a phase-to-phase fault as anything more than a slight overload.  As a result, the long-term thermal overload heaters of the overcurrent protective device (circuit breaker) may trip out this device long after an electrical fire has started. This thermal overload tripping is much slower, as opposed to a quicker, easier grounding path that allows the short-term magnetic armature to instantaneously remove the fault and preclude electrical shock and fires, as well as adhering to life safety and fire safety codes. With the PVC break, an electrical fire will in all probability be the heat source that trips out the circuit breakers thermal overload, as opposed to having enough time to heat it up and trip out the overload some six to ten hours later.

The way the PVC break detail is presently shown and required to be installed, the incoming ferrous conduit enters the perimeter wall and penetrates the secure area. By penetrating to the inside secure area, all radio frequencies and electromagnetic phenomena can be impressed upon the ferrous pipe and it will act like an antenna. Someone on the outside can then easily record this data and recreate the information that was propagated from within the secure area. If the length of metal conduit entering the facility prior to transitioning to the PVC break is as long or longer than the wavelengths we are interested in picking up, then we will have an unimpeded pick up and reception of that wavelength and frequency.

This detail indicates that the incoming ferrous pipe should stop just inside the exterior perimeter wall and make a transition to the polyvinylchloride, plastic, heavy wall conduit, once it is inside the secure area.  Once inside, another transition should occur from the PVC conduit back to the ferrous conduit. The other bad aspect of the PVC break is that the entering conduit is seldom grouted into the wall with cement nor rarely is it caulked all around. As a result, anyone can insert an insulated copper wire of adequate length (equal to or in excess of the wavelength to be measured) into and through the perimeter wall. Readings can then be recorded from this wire.  A partially insulated boom box antenna can be inserted through this unpared, unsealed opening and the signal transmissions can be recorded on magnetic tape.

Telecommunications equipment, computers and their attendant electrical wiring transmit electromagnetic waves from within the shielded area which are picked up by the control wiring and telephone wires thus, it is necessary that they also be RF-­filtered.

The following description of another approach to the standard PVC coupling detail might work even better if the incoming ferrous pipe stopped at the exterior perimeter wall and made a transition to the polyvinyl chloride, plastic, heavy wall conduit, which would then penetrate the perimeter wall where it would then re-emerge inside the secure area. Once inside, another transition should occur from the PVC conduit back to ferrous conduit. All sheet metal ductwork should transition to non-metallic bellow couplings where they enter and leave the tempest or SCIF room but may transition to sheet metal ductwork within the room.  When an office space is between floors occupied by other tenants and that space is being prepared as a SCIF, there are several things that need to be taken care of immediately in preparation for that transformation to even start. There will be electrical feeders and branch metal ductwork that must have a non-metal conduit, HVAC piping, cast iron roof drainpipes and HVAC ductwork that must have non-metal transition devices placed in them prior to their entering and immediately after leaving the space, such as PVC breaks and bellows couplings.  Signal strength that is broken and attenuated can’t be picked up by a listening device or recorder.

All electrical feeders, prior to entering a SCIF, HEMP facility or a tempest facility must be RF filtered. This RF-filter must be located next to and prior to penetrating the facilities shielded ceiling, floor or wall. All circuit and control wiring must be RF-filtered prior to exiting the SCIF, HEMP or tempest facility perimeter shielding.

The RF-filters are required not so much to prevent impressing a high frequency signal on and into the room or equipment but are designed to prevent or attenuate transmission of electromagnetic signals emitted by the secondary conductors, which act as antennas. These signals are the product of impulses generated from within the electronic devices of each computer or telecommunications device, which are transmitted via their respective branch circuit wiring and the associated power and panel feeders. Since the impulses can be reproduced by similar electronic devices, the recording of such signals could lead others to recreate the same computer printout programs or communications transmissions that would produce the same signal signature. It is for this reason that secure areas should have all conductors RF-filtered and all their floors, walls and ceilings electromagnetically shielded with lead, 22-gauge, nickel-plated sheet metal, sheet metal copper Sisal Kraft stock or copper paneled wood, or sealed with 3/8-in thick steel plate, bead welded all around.  Telecommunications equipment, computers and their attendant electrical wiring transmit electromagnetic waves from within the shielded area which are picked up by the control wiring and telephone wires thus, it is necessary that they also be RF-­filtered.


If these practical and common-sense approaches are utilized at the various secure government confidential facilities, the buildings can be made safer both for classified material processing and for security personnel.  We have focused upon the current state of the art, cutting edge of technology techniques, designs, details and methodologies for keeping our Embassies and their SCIFs secure as well as keeping our transmitting and/or receiving stations secure and functional and continuously operational under some of the most adverse conditions produced by both nature and man.  Other back up security systems such as cyphers, closed circuit television, and proximity entry cards or fascards, and personnel detection and intrusion devices should also be evaluated, analyzed and effectiveness comparisons made.

Harry Zacrikson, P.E., CVS, FIES, worked in facilities engineering for decades prior to his retirement. He can be reached at