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2017 | Buch

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Electronic Control Fires

A Design, Manufacturing and Forensic Technical Perspective

verfasst von: James E. Small

Verlag: Springer International Publishing

Buchreihe : SpringerBriefs in Fire

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Über dieses Buch

The failures of electronic controls, which can cause loss of life and property, are discussed from the perspective of both the design and manufacturing functions and clarified for the responsible forensic team. Many pitfalls of the fast-paced product introduction environment for industrial and consumer products are discussed to help minimize the number of electronic control fires and other menacing events of today.
The author clearly links the design, manufacturing and forensic technical communities in the development of electronic control devices, which include a wide array of products, from auto key fobs to furnace electronic control boards. The information included ensures a final product that will not end up in litigation (or at least not be found guilty during litigation), putting into plain words how to determine if a suspect electronic appliance control is the cause of a fire or the result of a fire.
Containing invaluable data learned through many years of new product designs, development and production cycles, this brief features illustrated bench experiments conducted by the author. Professionals and researchers working in fire protection, electrical engineering, or building safety will find this brief an essential resource.

Inhaltsverzeichnis

Frontmatter

Chapter 1. The Event Defined

Abstract

An engineer is summoned due to the infamous and dreaded event. This is the politically correct term for someone made a very serious mistake… attorneys will be involved… heads will roll… and fortunes may be lost. In the context of this book the short definition of an event is a smoke and/or fire occurrence when and/or where it is not expected and should not happen.

James E. Small

Chapter 2. Facts Regarding Typical Events

Abstract

An electronic control is sometimes accused of causing a fire if evidence exists of the product failing due to overheating. If a plastic housing or a printed circuit board, mostly intact with a localized area of black soot or other obvious visible damage, is found the first piece of the map that can ultimately lead to the root cause of the event is at hand and available. In the end perseverance through uncovering clues will lead to an understanding of why the event occurred and how to prevent it from occurring again.

James E. Small

Chapter 3. Localized Events

Abstract

MOVs (Metal Oxide Varistors) are often placed across AC power lines feeding a control. If there is inadequate current limiting into the MOV and the actual/fault maximum required MOV power dissipation is unknown, the MOV is susceptible to a very rapid explosive event that may result in a sustained fire if there is adequate fuel and oxygen in the immediate area.

James E. Small

Chapter 4. Who Is At Fault

Abstract

If you are fortunate a FMEA (Failure Mode Effects Analysis) will be available from the design organization. It will be very helpful to review it. It is entirely possible that you are witness to an anticipated failure mode. If this is the case your quest may indeed be over.

James E. Small

Chapter 5. High Current PCB Connections

Abstract

Current levels in the range of 3–18 A passing through PCB inserted connectors, copper pads and traces are not uncommon. When a hole is burned through a PCB at a high current connection such as this, it is due to one of five reasons. Note: Experiment #9b of Chap. 14 demonstrates that 4.7 W for 31 s (145.7 J) is adequate burn a hole through CEM-1 (94V-0). Experiment #6 of Chap. 14 demonstrates that 4.44 W for 52 s (230.88 J) is adequate to burn a hole through FR-4 (94V-0).

James E. Small

Chapter 6. Liquid, Moisture and Electronics

Abstract

Many are surprised to hear that water near an electrical appliance may cause an event. After all, water is used to put out fires, isn’t it? Water has an amazing ability to absorb large amounts of energy and therefore lower heat, resulting in slowing or extinguishing fires. This being said, water is very insidious when it comes in contact with electrical energy in its ability to conduct electrical currents and to form unwanted electrically conductive paths that can cause events.

James E. Small

Chapter 7. The Ugly Process

Abstract

Standard plastic material molded over two 120 VAC or 240 VAC pins will in all likelihood contain some level of mobile conductive material in the form of sulfur and/or chloride (Vicars et al. in Low Voltage The Incompetent Ignition Source - Dispelling The Myth, 2010, Sarasota, Fla. National Association of Fire Investigators, 2010, [1]). If these tiny ionic particles (bridge builders) are not capable of moving close enough to touch and then separate, there is no problem and therefore no event. This Ugly Process is also referred to as “Wet Tracking”.

James E. Small

Chapter 8. Liability Related Electronic Control Deficiencies

Abstract

(1)

Connector requirement and specifications are misunderstood:

(a)

Connectors are often chosen for a new design due to their success in a previous similar design without adequate FMEA (Failure Mode Effects Analysis). It is often the case that more of the available connections within a connector are used in a new application, without realizing the current rating of each conductor may be adversely affected.

James E. Small

Chapter 9. Localized Event Explained—Charred Hole

Abstract

Visual artifact

A charred hole is found at a high current (High ≥ 1 A) connector location.
Evaluation

In order to entirely burn away PCB base material a very intense arcing environment for ~1 min is required. For a 1.574 mm thick FR4 laminate this can occur with 39 J for 9 s to ignite and 47 J to sustain a flame for 11 s. This flame is capable of carbonizing the material that can fall out and leave a hole. For a 1.574 mm thick CEM-1 laminate this can occur with 27 J for 6 s to ignite and 157 J to sustain a flame for 35 s that is capable of carbonizing the material that can fall out an leave a hole. See experiments #5, #9a and #9b of Chap. 14 for comparative details.

James E. Small

Chapter 10. Localized Event Explained-Partially Charred Surface

Abstract

Visual Artifact

A partially charred surface area is found.

Evaluation

In order to burn away PCB surface material several things must be present:

(1)

A moist environment for several min at a time.

(2)

Repeated moist environment episodes in the presence of voltage and current.

(3)

An external supply of energy for a 1.574 mm thick FR4 laminate in the neighborhood of 39 J for 9 s to ignite and 47 J to sustain a flame for 11 s that is capable of carbonizing the material. For a 1.574 mm thick CEM-1 laminate this can occur with 27 J for 6 s to ignite and 157 J to sustain a flame for 35 s that is capable of carbonizing the material. See experiments #5, #9a and #9b of Chap. 14 for comparative details.

James E. Small

Chapter 11. Localized Event Explained-Scorched FR-4 with no Missing Weave

Abstract

A fiberglass laminate substrate is found with no missing weave. The epoxy layers are gone and a single layer of weave similar to a window screen remains intact.

James E. Small

Chapter 12. Localized Event Explained-Scorched FR-4 with Missing Weave

Abstract

A scorched laminate weave is found with missing material.

James E. Small

Chapter 13. PCB Smoke and Fire Damage for Power Levels Below 5 Watts

Abstract

Using Texas Instruments “Typical PCB Thermal Resistance Values”: 1000 °C will be generated within 0.032 thick FR4 laminate for each W of power flowing through a 1 cm² area. 1000 °C is well above the temperature required to ignite a PCB.

James E. Small

Chapter 14. Bench Experiments

Abstract

Mark Twain said “There are three kinds of lies: lies, damned lies and statistics.” Nothing will be inferred from the following and the reader is therefore encouraged to bask in the delight of the available data and any statistical inference he or she may find.

James E. Small

Chapter 15. Summary of Experiments

Abstract

Did not flame. • Visible smoke for 2 min 10 s. •Intense smoke for the last 20 s at which time it smoked for 2 min 20 s and then self-extinguished.

James E. Small

Backmatter

Titel: Electronic Control Fires
verfasst von: James E. Small
Verlag: Springer International Publishing
Electronic ISBN: 978-3-319-52845-8
Print ISBN: 978-3-319-52844-1
DOI: https://doi.org/10.1007/978-3-319-52845-8