English to Portuguese Tech/Engineering Mechanics / Mech Engineering

O termo "upset" aparece no contexto abaixo e estou na dúvida qual seria o significado em português. Sabemos q "upset" significa "transtornado" "zangado", etc....mas acho q não se encaixaria no contexto. Gostaria de sugestões! obrigada!

There is a unit upset and the relief valve fails to open, resulting in overpressure of the equipment and an "acute" release of flammable gas from a leaking flange. The amount released is above the 500 kg (within 1 hour) threshold. This is a reportable PSI. Releases from flanges are not excluded from PSI reporting.