Post-Crash Systems and Rescue

Post-crash safety starts after a collision has occurred: its job is to limit secondary harm, help occupants leave the vehicle, communicate the incident, control stored energy, and give responders accurate information for rescue, recovery, and later storage. It complements Structural Safety Systems, which manages impact loads, and Safety Testing, which explains test procedures and consumer ratings.

The post-crash sequence

Several actions may begin almost together when a severe impact is detected:

the restraint controller records the event and can send crash signals to other systems;
the electric powertrain can be disabled and high-voltage sources isolated from external circuits;
eCall can contact an emergency call centre and transmit a minimum data set;
doors may unlock, hazard lights may illuminate, and multi-collision braking may reduce further movement;
rescue information guides responders to batteries, high-voltage cables, cut zones, airbags, reinforcement, and manual disabling points.

The exact sequence depends on the vehicle and crash. A system that activates in one impact may not activate after a minor collision, damage while parked, or a charging incident. Responders therefore verify vehicle status and follow the information for the exact model rather than treating automatic activation as proof that every hazard has been removed.

Automatic high-voltage isolation

The traction battery is normally connected to the external High-Voltage System through controlled switching devices. UN Regulation No. 100 defines an automatic disconnect as a device that, when triggered, conductively separates electrical energy sources from the rest of the powertrain's high-voltage circuit. The regulation also distinguishes the battery system from the external circuit it supplies. UNECE — UN Regulation No. 100, Revision 3

A vehicle can open its main contactors after a qualifying crash. Some designs also use a pyrotechnic fuse or pyrotechnic battery disconnect. When commanded by crash or battery-control electronics, a small pyrotechnic charge drives a mechanism that permanently severs a conductor. Unlike a conventional fuse, it does not have to wait for sustained overcurrent before interrupting the path. Eaton — EV pyro fuse

Contactors and pyrotechnic devices have different jobs and may be used together. Contactors are controlled switches that normally open and close many times; the pre-charge circuit and their everyday operation are covered in High-Voltage Contactors and Pre-Charge Circuit. A pyrotechnic disconnect is a one-time device intended for rapid, irreversible interruption under defined fault or crash conditions.

Isolation has a precise boundary. Opening the external circuit does not remove the voltage or chemical energy inside the cells, internal busbars, or other parts on the battery side of the disconnect. Damaged power electronics may also retain charge briefly. Responders still treat the vehicle as potentially energized until its vehicle-specific procedure and measurements establish otherwise.

REESS: the stored-energy system

Rechargeable Electrical Energy Storage System, abbreviated REESS, is the regulatory name in UN Regulation No. 100 for the rechargeable system that supplies electrical energy for propulsion. The definition can include physical support, thermal management, electronic controls, and casing; an auxiliary battery used mainly for starting, lighting, or other low-voltage functions is excluded. UNECE — UN Regulation No. 100, Revision 3

In a battery-electric vehicle, the REESS is usually the complete traction-battery system rather than an individual cell. That distinction matters after a crash because safety depends on more than opening the external circuit. Pack retention, enclosure integrity, electrical isolation, electrolyte containment, fire resistance, and protection against electrical faults are separate layers.

UN Regulation No. 100 includes REESS tests for mechanical shock and integrity, fire resistance, external short circuit, overcharge, over-discharge, over-temperature, and overcurrent. Its vehicle-powertrain scope explicitly excludes road-vehicle post-crash requirements, while its REESS provisions can use crash-test evidence for mechanical integrity. Complete-vehicle electrical safety after impact is addressed through the applicable crash regulations and assessment procedures. The broader cell-to-pack failure chain is covered in Safety.

An automatic disconnect therefore answers only one question: whether the energy source has been separated from specified external high-voltage circuits. It does not prove that the pack is undamaged, thermally stable, or safe to open.

eCall and emergency communication

The EU's 112-based eCall system can be triggered automatically by on-board sensors or manually. It sends a minimum set of data over a public mobile network and establishes an audio channel between the vehicle and the appropriate public-safety answering point. European Union — Regulation (EU) 2015/758 on 112-based eCall

The minimum data set supports dispatch with information such as incident time, vehicle location, and direction of travel. Voice communication lets an operator speak with occupants when they can respond. eCall is an alerting and information system; it does not diagnose every injury or battery condition, and successful rescue still depends on local emergency services and the scene itself. European Commission — The interoperable EU-wide eCall

Third-party emergency-call services can add functions, but they should not be confused with the public 112-based system. Equipment, network support, market coverage, subscription terms, and the data available after a crash can differ.

Rescue sheets and emergency response guides

A rescue sheet is a concise, model-specific map for first and second responders. ISO 17840-1 defines its content and layout for passenger cars and light commercial vehicles so rescuers can find relevant structures and hazards while extricating occupants. The standard does not define the rescue process, responder training, or the method used to identify the vehicle. ISO — ISO 17840-1:2022 rescue sheets

An Emergency Response Guide, or ERG, is the deeper companion. ISO 17840-3 provides a template for information about immobilisation, hazard disabling, access, stored propulsion energy, fire, submersion, fluid leakage, towing, transport, and storage. Its headings align with the rescue sheet so the guide can extend the compact information rather than replace it. ISO — ISO 17840-3:2019 emergency response guide template

For an EV, useful rescue information can include:

traction-battery and high-voltage cable locations;
airbags, gas generators, pretensioners, and other pyrotechnic devices;
reinforced areas and recommended or prohibited cutting zones;
automatic and manual high-voltage disabling methods;
vehicle stabilisation and lifting information;
model-specific considerations for fire, water, towing, and post-incident storage.

The sheet must match the vehicle variant. A visually similar model, a different powertrain, or a facelift can place components and isolation points elsewhere. NHTSA's manufacturer-submitted collection illustrates the difference between the abbreviated rescue sheet and the more detailed response guide. NHTSA — Emergency Response Guides

Rescue, recovery, and delayed hazards

Post-crash rescue is wider than extrication. The response can include identifying the vehicle, preventing unintended movement, disabling ignition and propulsion, isolating stored energy, maintaining access to occupants, controlling fire or leakage, and planning towing and storage. Which actions are appropriate belongs to trained responders using local procedures and the manufacturer's exact guide.

For occupants and bystanders, the safe boundary is simple: do not touch exposed orange cables, damaged high-voltage parts, a leaking battery, or a smoking vehicle. Contact emergency services after a serious collision or signs of battery damage. NHTSA advises treating the high-voltage battery and associated components as energized and notes that physical battery damage can produce immediate or delayed fire and gas hazards. NHTSA — Electric and hybrid vehicle safety

Delayed hazards are why a vehicle may need monitoring after the visible incident has ended. External isolation cannot stop reactions already developing inside a damaged cell. Recovery, transport, and storage decisions must therefore consider impact location, pack condition, heat, smoke, sounds, warnings, and the manufacturer's instructions.

How post-crash performance is assessed

Euro NCAP's protocol used for its 2026 framework separates post-crash assessment into rescue information, post-crash intervention, and extrication. It reviews ISO-format rescue information, eCall data, multi-collision braking and hazard lights, electrical-energy isolation, thermal-runaway communication, and whether doors and belt buckles remain usable under defined conditions. Euro NCAP — Post-Crash Assessment Protocol v1.0

The protocol also checks electrical safety against applicable UN crash regulations and rewards clear automatic and manual high-voltage disabling methods with matching rescue-sheet instructions and markings. This is different from structural crash performance: a vehicle can protect the occupant space well yet make rescue information or post-crash access difficult, or do the reverse.

Assessment results remain programme- and year-specific. A rating summarises performance under defined procedures; it cannot guarantee the outcome of every road collision, battery event, submersion, or rescue operation. Read the exact result, test year, covered variant, and assessor comments alongside the vehicle's current rescue sheet.