Pipe Burst Electrical Voltage (Volts) Current (Amps) Resistance (Ohms) Insulation Resistance (Ohms) Electrical Flashover (arcing)
Electrical Malfunctions Isolated failures of specific items of electrical equipment, Failures of items of equipment that result in wider damage, and Electrical failures that lead to catastrophic damage such as a fire or an explosion. Electronic failure
Isolated damage to a complex item of machinery, or Possibly an injury, or A fire Electrical failure A fire, or An explosion, or A combination of both
Basic electrical causes of a fire or explosion Resistive heating defects, Tracking defects Electronic component failures Electrical malfunction continues to
evolve with the increase in portable and electronic equipment. An area of increasing problems involves lithium batteries SINGAPORE: On 8 November 2017 Channel News Asia:
Two fires caused by charging of e-scooters in two days The Singapore Civil Defence Force (SCDF) said on Wednesday (Nov 8) that there has been a spike in fire incidents involving personal mobility devices recently, with two such incidents occurring over the past two days. Families in Alabama, Louisiana, Florida, Hong Kong, and London
have seen their houses burn after the boards burst into flames during charging. Of 17,000 hoverboards inspected by the UKs National Trading Standards since October, 15,000, or 88%, are unsafe, because of issues with the plug, cabling, charger, battery, or the cut-off switch
High profile recalls 2005: Dell recall approximately 22,000 laptop computer batteries and another 4.1 million a year later due to risk of fire or explosion, 2007: Nokia recall 46 million batteries due to risk of overheating, 2012-13: Apple recall some MacBook Pros due to battery issues, 2013: All Boeing 787 Dreamliner's grounded due
to a risk of the lithium batteries overheating and catching fire, 2016: Samsung recall 2.5 million Note 7 smartphone batteries after 35 confirmed fires and shortly after they recall all Note 7s due to further battery problems. Why use lithium batteries? High specific energy density, The ability to discharge and recharge them fast,
Long cycle life, Low self-discharge rates, Lack of a memory effect, Absence of toxic heavy metals Basically it is our desire to have smaller devices with ever greater duration that has driven the significant increase in their use. The issues with Lithium cells Essentially they require careful management as:
Overcharging can lead to thermal runaway and catastrophic failure Overheating can result in thermal runaway and catastrophic failure Short circuiting can lead to thermal runaway and catastrophic failure Over-discharging can cause internal changes that can lead to thermal
runaway and catastrophic failure when the cell is next charged They cannot be fast charged at low temperatures (below 0C) for similar reasons So what does a catastrophic failure look like? Key questions: 1) Why do they fail in such a violent manner? 2) What causes them to fail?
3) How can failures be prevented? The risk of a violent failure stems from: Their high energy density A flammable electrolyte (i.e. their chemistry) and The possibility of an exothermic
reaction that can occur between the electrodes and the electrolyte that can lead to rapid thermal runaway. Basic cell components A cathode (+ve electrode) An anode (-ve electrode) An electrolyte (conductor
of ions) Discharge: the anode loses electrons (it oxidises) and the cathode gains electrons Charge: the reverse occurs LI-ION CHEMISTRY AND CONSTRUCTION Positive electrode (cathode) materials: Lithium cobalt oxide (LiCoO2)
Lithium manganese oxide (LiMn2O4) Lithium nickel oxide (LiNiO2) Lithium iron phosphate (LiFePO4, or LFP) Electrolyte materials: Typically Lithium salt (LiPF6) Negative electrode (anode) materials: Graphite is by far the most common
Other materials are under development Prismatic Cylindrical , e.g. 18650 Pouch Coin
Primary causes of catastrophic failure: Over-charge Over-discharge Short circuit Lithium dendrite growth Manufacturing defects Mechanical damage Cell reversal
} All these aspects can and should be controlled and managed by battery management circuitry Over-charge
Lithium-ion cells are highly voltage sensitive Charging a cell Li-ion cell to a voltage greater than 4.2V, even by only 0.05V, can often result in thermal runaway and catastrophic failure Reaction between Cathode electrode material and the electrolyte => internal heating => pressure build up => venting, and
=> possibly fire Over-discharge Discharging a Li-ion cell to a voltage less than 2.5V can result catastrophic failure due to either: Migration of the copper current collector into the anode material => internal short circuit and => fire Capacity loss and swelling
=> catastrophic failure when the cell is recharged Short Circuit A short circuit across output terminals will allow high currents to flow, which are only limited by the low internal resistance of the cell: 3.7 =148 25
I R 148 2 25 = . V
The power dissipated in the cell causes it to rapidly overheat => production of flammable vapour and => fire or explosion All the foregoing can be avoided with proper battery management Electronic circuitry should prevent over-charge, over-discharge or excessive current flowing in the event of a short circuit The circuitry can, however, be fitted
directly inside the cell or in the external circuit (charger or appliance), surely a recipe for disaster! Two 18650 cells Electronic Cigarettes
Were the Fire Service findings correct? The two most common types of E-Cigarette together with their charging adaptors.
The adaptor connects the battery to a suitable USB power socket There are, however, different adaptors Some adaptors have the battery protection circuitry within them, while others are for cigarette batteries that have the charging circuitry in the battery.
The two types of adaptors are, however, interchangeable with one another. Samsung Note 7 The available information indicates the first and second recalls were due to different problems, albeit both were associated with the lithium batteries
In the original recall the battery was reportedly too big. A short circuit developed at the edge of the battery. Defect further complicated by the negative electrode being incorrectly located in the curve of the jelly roll The second recall Poor construction of the replacement batteries Primary cause welding burrs on the positive electrode
Secondary cause Some batteries were missing insulation tape In Summary As electronic devices develop and electrical equipment becomes ever more prevalent, new problems will inevitably arise. Lithium cells are currently one of the more problematic items, although the issues associated with them are becoming ever more understood.
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