Short answer. The proprietor of the premises. Article 2191 makes proprietors responsible for damages caused by the explosion of machinery which has not been taken care of with due diligence, and by the inflammation of explosive substances which have not been kept in a safe and adequate place.
What the law says
By the explosion of machinery which has not been taken care of with due diligence, and the inflammation of explosive substances which have not been kept in a safe and adequate place
Civil Code, Article 2191 — Other Liabilities of Proprietors. Read the full provision →
Maintenance is written into the rule
The article does not make every explosion the neighbour's responsibility. It fastens on machinery which has not been taken care of with due diligence, so the failure of care sits inside the rule rather than having to be proved separately as ordinary negligence. In practice that moves the argument to the maintenance history: when the machine was last serviced, whether known faults were left unattended, whether it was run past its capacity. A proprietor who can show a diligent regime of care is arguing inside the article's own words, and so are you when you show there was none.
Two situations, failing in different ways
The paragraph actually covers two things. The first is the explosion of machinery not maintained with due diligence. The second is the inflammation of explosive substances which have not been kept in a safe and adequate place, which is about storage rather than upkeep: fuel, gas cylinders, chemicals, kept where they should not have been. If what went up next door was a stored substance rather than a machine, the question is not how well it was serviced but where and how it was held, and whether that place was safe and adequate for that substance.
Who the defendant is, and when it changes
The article names the proprietor, the person holding the premises where the machinery or the substance was. That is workable for a neighbour, who has no way of knowing what goes on inside. There is one redirection worth knowing about. Article 2192 provides that where the damage results from a defect in the construction mentioned in Article 1723, the third person suffering damage may proceed only against the engineer, architect or contractor, in accordance with that article and within the period fixed there. So the shape of the claim can change once the cause is established.
The scene will be cleared within days
Act before it is. Photograph the debris, the machine and the damage to your own property from several angles, and keep anything that landed on your side. Note the date and time and who else saw it. Fire or police records of the incident are worth requesting early, while they are easy to get. On your side, obtain a repair estimate and, if anyone was hurt, the medical records. Any earlier complaint about noise, fumes or leaks from that machinery is now evidence that the problem was known and left alone.
Related provisions
- Civil Code, Article 2192 — When the Engineer or Architect Answers
- Civil Code, Article 2190 — Liability for a Collapsing Building