Overcharging Incident

In a multiprocess train building, an operator was running several batch polymerization reactions. One of these was a copolymerization process involving two monomers, an initiator and an organic solvent. Several of the other processes 

At shift change the operator verbally told the relief operator what process steps remained. The relief operator tested for, and detected unreacted monomer in the copolmerization process. In an attempt to complete the reaction, the relief operator added additional initiator to the reactor a runaway reaction promptly occurred. 

No injuries occurred but the rapid emission of the organic solvent overpowered the incinerator, causing it to shut down and resulted in a release to the environment. 

After the incident, an investigation team determined that the first operator had not added the initiator when required earlier in the process. When the relief operator added the initiator, the entire monomer mass was in the reactor and the reaction was too energetic for the cooling system to handle. Errors by both operators contributed to the runaway. Both operators were performing many tasks. The initiator should have been added much earlier in the process when much smaller quantities of monomer were present. There was also no procedure to require supervision review if residual monomers were detected. The lesson learned was that operators need thorough training and need to be made aware of significant hazardous scenarios that could develop. 

Operating procedures must be written to clearly identify safety issues. Supervisors must be contacted when process conditions deviate from normal. Proper time and procedures must be maintained to transmit information at shift change. 

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Safety has been the subject of study at Harwell and no incidents were observed when the cells were (i) overcharged and overdischarged (C/10, C and 10 C rates) (ii) short-circuited (iii) forced to discharge (iv) heated above 400°C, and (v) cut open. It must, however, be recognized that the evaluation was run on test cells and thus that the safety characteristics of large units may be still a matter to be ascertained. 

Lithium-ion Batteries, safety provides an overview of the safety considerations for Li-ion cells. Presently, Li-ion cells have a record of field failures or safety incident of one incident every ten million cells. The 18650 cell used in portable electronic applications contains sufficient energy to self-heat the cell to over 600°C. This does not include oxidation of the electrolyte solvent by the cathode oxide materials. AdiabaticaUy, including the electrolyte, the temperature is significantly higher. The causes of an incident include overcharge and heating from external sources. AU cells have safety devices such as PTC, CID, vents, and safety circuitry. An internal short is the most common trigger for a safety incident. 

Field failures typically represent unprovoked battery explosions and according to industry experts such events are rare and is estimated that one in 10 million Li-ion batteries fails that way [10]. Field failures are more challenging to reproduce and study in a lab because they happen so infrequently. Moreover, these incidents stand in contrast to failures of abuse-tolerance tests, in which batteries are methodically subjected to extreme conditions such as uncontrolled heating, overcharging, crushing or puncturing to assess the battery s response. Another difficulty in analyzing the causes of spontaneous failures is that batteries that fail in the field come from lots that have already passed abuse and reliability tests, and they appear to have worked normally. 

Fire detection capability is considered optional as the batteries themselves have little combustibility and only a limited amount of cabling or charging equipment is normally provided. A fire incident has a low probably of occurring, while historical evidence indicates the buildup of hydrogen vapors (possibly by fan failure or battery overcharging) and a minor room explosion as the likely incident to occur and damage the contents of the room. 

S-2 Demand Operator error -overcharged reactor Serious Incident Report 18 L. Soft... 

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