Halon and cellular phone

Here is a follow-up to the enquiry about Halon systems being activated
by cellular phones.

  Paul Baril
  CCI
  Date: 16 Dec 96

  Summary:
  Comments received to date from the fire protection field show a
  reasonable support to believe portable radios (walkie-talkies) can
  cause microprocessor-based fire alarm systems to activate. Older
  relay type fire protection systems appear to be safer from this
  problem. Some manufacturers have designed their systems to
  minimize this risk. There's little support to believe cellular
  telephones can cause fire protection systems to activate.

  It may be wise to keep a distance of 8 to 10 feet from fire alarm
  panels and smoke detectors when using portable radios.

  For more information please see the abbreviated comments below.

  Paul Baril
  Canadian Conservation Institute

  1. John M. Cholin, P.E.

    RF interference is not a pervasive problem but does raise its
    ugly head with certain installations and with certain products.
    When it raises its head it is generally very ugly! There are
    tons of information on RF interference in the electronic
    engineering community. There is an entire cadre of EEs that do
    noting but resolve RF interference problems.  There is a
    tremendous wealth of info available from the IEEE.  Fortunately,
    most RF interference problems encountered in the fire alarm
    industry are relatively simple ones that are quite soluble, even
    by guys like me!

    RF susceptibility is found in two areas of the fire alarm
    system: detectors and control panels.  Let's deal with the
    detectors first. In order for a detector to be truly RF immune
    its circuit must be symmetrical about earth-ground.  For example
    the impedance from the positive power supply and the negative
    power supply to ground should be the same.  If not the RF will
    impose an asymmetric charge across any and all diode junctions in
    the circuit--often with very strange, if not amusing results.
    Naturally the most susceptible portion of a detector circuit is
    going to be the "front-end", the part that does the sensing.
    This is an area where there are important performance
    differences between ionization and photoelectric detectors.

    Ionization detectors use a junction field effect transistor
    (JFET) as the front end component.  JFETs are symmetrical die
    devices! Since symmetry is good RF immunity--you guessed it--JFET
    front ends in ionization detectors are generally fairly RF
    immune.  On the contrary, the front-end of a photoelectric
    detector is either a phototransistor or a photodiode.  These are
    asymmetric components by their very structure and will rectify
    any RF in the neighborhood, resulting in spurious charge
    accumulations in the pre-amplifier stage of the detector
    and--you guessed it- trouble in river city!  While an artful
    electronic engineer can design compensation circuits for any
    given RF transmission the compensation circuits at one frequency
    band are generally not so hot in some other frequency band.
    Consequently, occasionally we hear of a detector model that has
    developed a problem with some type of RF transmitter.  The
    better manufacturers are quick to develop solutions for those
    problems.

    The second point of vulnerability is the control panel.  When I
    make that statement I am considering the installation wiring as
    part of the control panel because it is the antenna! Here again,
    RF immunity is largely controlled by the degree of circuit
    symmetry in the control panel.  Systems with symmetrical power
    supplies about earth-ground are generally more RF immune.
    Symmetrical initiating device circuits also contribute
    substantially to the stability of the FACU. Most panels
    available today are test for RF interference by the NRTLs and
    will provide stable service when properly installed.  Indeed,
    the overwhelming majority of the RF interference problems I have
    encountered in my engineering practice have been the artifact of
    substandard installation practices.  Most of the current systems
    I have studied have a high degree of RF immunity built into
    them--this is a well understood topic amongst the hot-shot EEs.
    However, that RF immunity will breakdown if the proper wiring
    methods and materials are not employed.

    Asymmetric impedances along the wiring turn the symmetric power
    supply at the control panel into an asymmetric power supply at
    the distant detector with those strange and sometimes amusing
    results. In general, the faster the system transmits data the
    more susceptible it will be to some form of RF interference
    either in the form of data integrity or analog signal.  However,
    the newer, smart software can do a lot to restore degraded data.

    The bottom-line is to choose a quality manufacturer and a
    quality installation contractor and follow the installation
    practices meticulously.  That will avoid 99% of the problems
    right at the start. If you buy the project on a strict low-bid
    basis don't be too surprised if you get what you pay for!

  2. Steven Germano  Factory Mutual Engineering
  Re: RF effects on smoke sensors

    When I used to work at Factory Mutual Research in the 80's, we
    added a walkie-talkie test after hearing of complaints of false
    alarms due to RF.  I believe we keyed a 5 watt Motorola walkie
    talkie at a distance of 1 ft. away from the detector (and also
    the control panel).  We didn't fail the equipment if it false
    alarmed, but made note of it. Early on, the microprocessor based
    equipment had some problems with RF, but I believe the
    manufacturer's corrected the situation.

    The possibility certainly exists that a two way portable radio
    can cause a control panel to false alarm. At a large military
    installation, I witnessed this happen on three separate
    occasions. One involved a building fire alarm control panel
    which was over 12 years old; the second  during the acceptance
    testing of an Inergen control panel; the third involved a Potter
    land line transmitter. On each occasion a person was standing
    directly in front of the control panel while transmitting on a
    Fire Dept. radio. These radios also caused similar problems with
    other electronic equipment. The base Fire Dept. has since
    changed portable radios and I am not aware of any recent
    problems.

  3. Carroll W. Wollard II, President, Fire-X Sales & Service Corp.
  Hagerstown, MD.

    The possibility certainly exists that a two way portable radio
    can cause a control panel to false alarm.  At a large military
    installation, I witnessed this happen on three separate
    occasions. One involved a building fire alarm control panel
    which was over 12 years old; the second  during the acceptance
    testing of an Inergen control panel; the third involved a Potter
    land line transmitter. On each occasion a person was standing
    directly in front of the control panel while transmitting on a
    Fire Dept. radio. These radios also caused similar problems with
    other electronic equipment. The base Fire Dept. has since
    changed portable radios and I am not aware of any recent
    problems.

  4. John Grocke

    I have heard stories of walkie-talkies tripping fire suppression
    systems that used older style releasing control panels that did
    strange things when exposed to RF interference.  A few years
    ago, while at a NASA facility at Kennedy Space Center, I saw an
    old releasing panel on a wall with an engraved sign that read
    "DO NOT OPERATE WALKIE-TALKIES OR PORTABLE RADIOS WITHIN 3 FEET
    OF THIS CONTROL PANEL".  While servicing old Halon and other
    releasing panels years ago, I was always told not to operate
    walkie-talkies with the control panel door open for this reason.
    I realize that this is not documented proof of this phenomenon,
    but thought it might help.

  5. Charles Sabah

    I doubt that a cellular phone has the power and the frequency
    that would affect a Halon system. We have installed close to
    three hundred(300) Halon systems in cellular phone switch sites
    without a single unwanted discharge.

  6. Kevin R. Dixon, Fireline Corporation, Leesburg Branch

    I have seen 2 way radios drive a system into alarm when too
    close to the panel.  This seems to especially be true when
    working on an intelligent system.  If the panel is used for
    suppression, it is a very real possibility.  My advice from
    personal experience, keep at least 3-5 feet from the control
    panel when using 2 way radios.

  7. Fred K Walker, Usaf Chief Fire Engineer Hq Afcesa/Cesm

    We have not had any Halon systems activated by phone or radio
    transmission but we have had other systems especially systems
    using optical flame detectors activated in this manner.

  8. Ian W. Price, P.Eng. Principal, Emergency Communications
  Engineering

    It's been my experience that RF interference from walkie-talkies
    can affect fire-alarm/suppression-system control panels
    generally only when the panel is open and there is no shielding
    from the RF between the radio antenna and the PC
    boards/components. The warnings to technicians are real and
    valid, since most testing is done with walkie-talkies when the
    panel is open. False system operation due to 'operations' -type
    radio communications between say security guards in a building
    when the FA is not being serviced, have not come to my attention
    ... although that's not to say it never has, or cannot, happen.

    Both Canada and the US have rules governing the RF emissions
    caused by electronic equipment (FCC Part 15); I'd check the
    UL/ULC Control Panel manufacturing standard (in Canada,
    CAN/ULC-S52? [reference not handy]), for a specification for
    resistance to RF interference. It would surprise me to find
    there was none.

    Here are some generalizations--treat them as exactly that .... If the
    control panel is in a grounded metal box with the door closed, the RF
  can't get in; Cellular phones have a lower power output than
  walkie-talkies.

  9. Joe Levesque, Fire Protection Engineer, Brookhaven National
  Laboratory

    Over the past 40 years we have seen our 150 relayed based fire
    alarm panel change to micro processor based "intelligent"
    panels.  We now have over 100 micro processor based panel and
    less than 80 relay based panels.  The relay based panel do not
    react to RF (from our VHF maintenance radios).  The
    microprocessor based units do. The  RF interference only occurs
    from the portables when the Fire Alarm Panel door is open.  We
    have never tripped a system, but the panels can do all sorts of
    weird things (reset, alarm, go into trouble).

  10. Mark Chubb, Fire Code Coordinator, Southeastern Assn of Fire
  Chiefs

    RF emitters, especially FM radio transmitters, have been known
    to initiate high-explosives such as blasting caps and detonating
    cord. Explosive squibs used to release Halon are essentially low
    energy detonators.  The leads on the squib may act like an
    antenna and induce a small current in the device, initiating the
    explosive material inside.

    The sensitivity of certain explosive materials and devices to RF
    initiation is the reason you see warning signs entering and
    leaving blasting sites warning you not to operate radio
    transmitters.

  11. Carroll W. Wollard II,  President,  Fire-X Sales & Service Corp.

    Forklift emissions can also cause accidental discharge of halon
    systems when used to maneuver new equipment installations in
    existing halon protected areas (such as flight simulator
    hangers).

  12.  C. Burton Ford

    There are lots of cases where walkie-talkies have alarmed smoke
    detection systems some of which were connected to special hazard
    suppression systems (Halon, CO2, preaction, etc.) Usually this
    did not result in discharge due to the redundant requirements
    ala cross-zone, priority matrix. Occasionally it did result in a
    discharge. It seems that control panels may be as vulnerable as
    smoke detectors to RFI. I expect that the list will give you
    more gory details.

  13.  Andy Leneweaver, Fire Chief Equipment, Bellevue, WA

    As a field service technician, in years past, I have personally
    set off many different alarm systems (addressable and hardwire),
    by exposure to radio transmission, and have heard many more
    first hand reports of security personnel setting off systems
    (including suppression systems) by transmitting near the control
    panel.  Keystone Fire Protection, in the Philadelphia, PA area,
    even had labels made to alert occupants of the possibility of
    accidental discharge by radio. Luckily, during the times I set
    off systems by radio, the systems were disabled and being
    tested.  Some of the security personnel were not so lucky.

  14.  John M. Lawlor, President, Keystone Fire Protection Company

    My guess is that you will unleash a 7-day deluge of responses on
    this subject, but the answer to your question about walkie
    talkies causing unwanted discharges of Halon systems is an
    unqualified "YES".  We have had numerous examples in the past 10
    to 15 years of radios "spiking" microprocessor based control
    panels, with the most undesired result being accidental
    discharge of the connected system.  Many years ago, we invested
    in very conspicuous 3" X 4" bright orange decal that we place on
    the front of all of our installed suppressions system that
    states:

      "WARNING:  Do not use radio communication equipment within 10
      feet of the fire control panel."

    We ate a few unexplained discharges in previous years before we
    figured out what was happening.  If you've had an unexplained
    loss, it is very possible that RF interference was the culprit.
    It certainly is an easy test to repeat (with the control heads
    off the cylinders of course).

  15.  Robin Justice, FSS-21, Los Alamos National Laboratory

    A while back (when this thread was first visited), I committed a
    faux pas and posted a message that stated that FCI panels also
    had this problem. Turns out that the newest FCI panels don't.
    The owner of the company has spent major money to harden his
    company's panels against RF. You might consider going to them.

David Tremain
CCI

                                  ***
                  Conservation DistList Instance 10:58
                Distributed: Tuesday, December 17, 1996
                       Message Id: cdl-10-58-016
                                  ***