Do Not Microwave

The letter arrived before the device did.

This is not unusual in personal injury cases. The legal correspondence tends to move faster than the evidence, carried along by urgency and the particular momentum of a person who has been hurt and is looking for someone to be accountable to. What was unusual was the tone of the room when we received it. Personal injury escalations have a characteristic energy — focused, urgent, slightly adversarial, everyone leaning forward. This room was quieter than that. Someone mentioned early on that the customer was elderly. Nobody said anything in response, but it settled over the meeting in a particular way, and we proceeded more carefully than we might have otherwise.

The letter described significant injury. A burned hand, hospital treatment, bandages, bills. Photographs of the device — a consumer wireless product, the kind carried on the body through an ordinary day — showing severe charring on the exterior. A threat to report to the CPSC. A request for compensation. Behind the legal language was the account of a woman who had experienced something frightening in her own home and did not understand what had happened or why.

We requested the device and waited.

When it arrived we began where we always begin — with the energy sources.

Thermal damage of this severity requires a source. In consumer electronics that source is almost always one of two things: power from the wall, or power from the battery. Everything else is downstream of one of those two inputs, and the investigation is largely a matter of tracing the energy back to its origin. We checked the power adapter and the charging cable first. The customer had indicated the device was not plugged in at the time of the incident, and the cable showed no damage consistent with a fault — no melting at the connector, no heat damage along the length, no evidence of arcing or overcurrent. We set it aside.

The battery was next. A lithium pouch cell, partially visible through the damaged enclosure. There was thermal discoloration present, concentrated at one corner of the cell. We looked at it carefully under magnification, looking for the signature of an internal failure — the kind of damage that originates from within the cell and propagates outward. Electrolyte venting. Separator failure. The characteristic outside of a cell that has experienced thermal runaway looks different from one that has been heated externally, and this one had been heated externally. The damage pattern was outside-in. The cell itself was largely intact and still held a charge. We ruled it out as the energy source.

What remained was the printed circuit board.

The charring was significant. Consumed copper, burned solder mask, melted plastic in the surrounding enclosure. Whatever had happened here had released a meaningful amount of energy into a concentrated area. We pulled the layout files and the schematic and oriented ourselves — locating the power management circuitry, the charging circuit, the high-current rails, the components most likely to be involved in a resistive fault or a short. We were looking for the intersection of available energy and the damage site.

The damage site was not near any of them.

We looked again. The charring was located in a region of the board that was, by any conventional electrical analysis, uninteresting. No significant power rails in the vicinity. No high-current components. The circuitry in that area was low-power, signal-level, not the kind of thing that accumulates or dissipates enough energy to char a board. We pulled up the layout on a larger screen and looked at the area in context.

It was the antenna.

The antenna region of a consumer wireless device is, electrically speaking, a quiet neighborhood. The transmitted power of a device like this is regulated, limited, measured in milliwatts. The antenna does not generate heat under normal operation. It does not generate heat under abnormal operation in any failure mode we had encountered. If you were to short the antenna to ground, you would disrupt the wireless function of the device. You would not burn the board.

We sat with this for a while.

The conversation that followed was the kind that happens when a room of engineers has eliminated every conventional explanation and is beginning to feel the edges of the problem space. Someone suggested a component defect. We looked — nothing in the area that could account for the energy. Someone suggested a manufacturing fault, a solder bridge, a contamination-driven conduction path. We looked — nothing. The board in that region was clean except for the thermal damage itself, which was extensive and which had clearly originated there and not migrated from somewhere else.

Someone made a joke about a hacker. A remote attack. Something transmitted wirelessly that had overwhelmed the antenna circuit. There was brief laughter, the kind that happens when a room is tired and slightly frustrated.

And then someone said the word wireless, and the laughter stopped, and we looked at the board again.

The antenna receives RF energy. That is what antennas do — they convert electromagnetic radiation into electrical current. Under normal operating conditions the energy levels involved are low, the circuit is designed for them, and everything functions as intended. But an antenna does not discriminate. It receives what is present in its environment. And if the RF energy present in its environment were to exceed, by a significant margin, anything the circuit was designed to handle —

We looked at the damage pattern. Localized. Intense. Consistent with a rapid, high-energy event rather than a slow resistive fault. Consistent with an antenna circuit that had received more energy than it was built to absorb.

We looked at each other.

The hypothesis, stated plainly, was this: the device had been placed inside a microwave oven and the microwave had been operated.

It was an unlikely hypothesis. It was also, given everything we had eliminated, the one that remained.

We set up the replication on a bench in the lab with an exemplar unit and a standard consumer microwave oven. We documented the initial state of the device. We placed it inside. We set the timer for twenty seconds.

At the end of twenty seconds we stopped the microwave and removed the device.

The damage pattern was identical. Same location on the board. Same severity. Same consumed copper, same burned solder mask, same melted plastic at the enclosure. Twenty seconds had produced, with precision, exactly what we had received in the mail from a frightened elderly woman who had not told us how it happened.

We did not need her to.

What we needed to understand was why.

Not the physics — the physics was resolved. RF energy from the magnetron, received by the antenna, dissipated as heat into a circuit not designed to handle it. Twenty seconds at standard microwave power is sufficient. The replication had confirmed this without ambiguity.

What we needed to understand was what had led a person to place a consumer electronics device into a microwave oven. Not because the answer would change the forensic conclusion — it would not — but because it would determine what the response should be.

We made contact through the customer service team. The conversation was handled carefully, without accusation, framed as an effort to understand what had happened so the company could help appropriately. The account that emerged was straightforward and, once we heard it, entirely predictable.

The device had gotten wet. A kitchen incident — water, a sink, the ordinary domestic accident that happens to everyone eventually. The lady had done what she understood to be the right thing. She had tried to dry it out. She knew that heat dried things. She knew that the microwave produced heat. She had used the microwave to dry things before — a damp cloth, leftover food, the practical applications of a kitchen appliance she understood in practical terms. She did not know what an antenna was. She did not know what RF energy was. She did not know that the interior of a microwave oven is an environment that consumer electronics are not designed to survive.

She had put the device in for a short time, she said. Just to dry it.

When she opened the door there was smoke. She reached in and burned her hand on the device. The burn required medical treatment. She had been frightened and in pain and she had written to the company because she did not know what else to do and she believed, genuinely, that something had gone wrong with the product.

Something had. It was not what she thought.

The question of what to do with a finding like this is not a forensic question.

The forensic question was answered on the bench in twenty seconds. Customer-induced. Replication confirmed. The device had performed exactly as designed in every respect. There was no defect. There was no manufacturing fault. There was no design flaw. The company had no regulatory obligation to report and no technical liability for the damage.

What remained was a woman with a burned hand and hospital bills and the memory of smoke in her kitchen, who had done something that seemed entirely reasonable to her and had been hurt by the consequences.

We paid her medical bills. It was not a large amount. It was not accompanied by an admission of liability. It was accompanied by a letter that was carefully worded in the way that letters in these situations are always carefully worded, which is to say it said a great deal without quite saying anything.

And then someone designed a label. Small, simple, the kind of thing that goes on the inside flap of a box alongside the other warnings that nobody reads until after something has happened. A pictogram of a microwave with a line through it. A few words.

Do not microwave.

There is a saying in product safety that every warning label is a scar. It exists because something happened — because someone, somewhere, did the thing the label now prohibits, and was hurt by it, and the company learned something it had not known before about the distance between its assumptions and its customers' understanding of the world.

The engineers who designed this device understood antennas. They understood RF energy and magnetron output and the behavior of copper traces under thermal load. They had thought carefully about the ways the product might fail and had designed against those failures with diligence and competence.

They had not thought about the microwave. It had not occurred to them that it needed to be thought about. The gap between what they knew and what they assumed their customers knew was, to them, invisible — because when you understand something thoroughly it becomes difficult to imagine not understanding it. The knowledge occludes the gap.

The old lady had closed that gap for them. It had cost her a burned hand and a frightening afternoon and a medical bill that the company paid without admitting it owed.

The label on the box now costs a fraction of a cent per unit. It will prevent, over the lifetime of that product line, some number of incidents that will never be counted because they will never happen. The people it protects will never know it protected them. They will open the box, glance past the warnings, and go about their day.

That is, in its quiet way, what the job is for.