National Fire Protection Association (NFPA)
https://www.nfpa.org โบ fire-investigator โบ pres921gd
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NFPA 921
GUIDE FOR FIRE AND EXPLOSION INVESTIGATIONS [2021]
๐๐ก๐ ๐๐ข๐ฌ๐๐จ๐ฏ๐๐ซ๐ฒ ๐๐ง๐ ๐๐๐ข๐๐ง๐๐ ๐จ๐ ๐๐ฆ๐๐ซ๐ญ ๐๐๐ญ๐๐ซ ๐
๐ข๐ซ๐๐ฌ
INTRODUCTION TO THE DISCOVERY OF RADIO FREQUENCY RADIATION AND THE RELATED BREAKDOWN OF ELECTRICAL WIRING INSULATION LEADING TO FIRE CAUSATION
Presented by:
Jim Brown, CCAI-CFI
Fire Forensics & Technology
Presented by
Dr. Robert Armstrong, PhD P.E.
Armstrong Engineering
Dr. Vytenis Babrauskas, PhD
Fire Science and Technology Inc.
๐๐๐๐ฅ๐๐๐ง๐๐ฅ๐๐ฆ๐ง๐๐๐ฆ ๐ข๐ ๐ฆ๐ ๐๐ฅ๐ง ๐ ๐๐ง๐๐ฅ ๐๐๐ฅ๐๐ฆ ๐๐ฅ๐ข๐ ๐๐๐๐๐ ๐ข๐๐ฆ๐๐ฅ๐ฉ๐๐ง๐๐ข๐ก
Occur within 1 month to two years following initial replacement of analog
meter with smart meter
โข Within 15 โ 25 feet of smart meter
โข Occur in continuous sections of branch circuit wiring, not at points of
connection or splices, not near staples, not in junction boxes
โข No evidence of insect or rodent infestation
โข Occur in void spaces (walls, ceilings) and in attics with no human activity
โข Often small fires (5 โ 10โ diameter)
โข No correlation to service size or circuit loading
โข No correlation to premises wiring age or material (Al or Cu)
โข No correlation to significant weather events (lightning)
โข No evidence of utility supply (distribution) system anomalies (voltage spikes)
โข Fires cause typically listed as UNDETERMINED
5 STAGES LEADING TO FIRE
โข 1st Stage: RF pulses (beams) away from meter in a specific pattern to send signals (data) to nearby meters in the โDaisy Chainโ
โข 2nd Stage: RF from meter bounces off โreflectedโ surfaces causing RF to โdouble/quadrupleโ in intensity (in terms of energy density measured as microwatts per square meter; ฮผW/m2). The pulse bounces back and onto the oncoming pulse and intersects at a specific geometric focal point. If PVC insulation is present at that focal point, the RF energy can get converted to heat energy in the dielectric, causing micro fractures or bubbles in the polymer. The main effect is likely thermal, but the existing electric field
may accelerate the degradation of the polymer (PVC)
โข 3rd Stage: Sufficient heating can either ignite the polymer directly,
or, more likely, first carbonize it. If PVC gets carbonized, then this
can be the initiation of arc tracking, and arc tracking can end up in
ignition.
โข 4th Stage: If wood structural members are near/touching, this
resistive heating can initiate and sustain pyrolysis of wood.
โข 5th Stage: Flaming combustion begins.
TYPES OF SMART METER FIRES
Smart-meter-caused fires can be grouped into three broad
categories:
1) Inadequate mechanical or electronic design of the meter.
โข Example: Overheating component(s) inside meter; water ingress into
electronics due to poor sealing; inadequately-sized shut-off relays
causing fire upon remote re-energization; faulty Li-ion batteries (note
that mechanical meters do not need one).
2) Problems at the meter/base stab connections.
โข This has nothing to do with the โsmartโ aspects. Usually due to an
untrained gorilla force-fitting the new meter onto the base.
3) Ignitions of wiring at some distance from the meter.
โข This is the sole topic of our presentation today. #1 and #2 are fairly well
understood and not particularly controversial.