Electric vehicles still share many familiar components with conventional vehicles; brakes, steering, seats, seat belts, body structure, and visibility-related equipment in an electric vehicle must also meet their respective safety requirements. The main difference becomes apparent when the electric propulsion system, high-voltage circuits, and battery pack are added to the vehicle. In addition to the conventional hazards associated with a vehicle, issues such as electric shock, short circuits, battery temperature rise, fire, mechanical damage to the energy storage system, and the behavior of the electrical system after a crash must also be considered.
For this reason, evaluating the safety of an electric vehicle cannot be reduced to a single “battery test.” Safety must be assessed at several levels: the vehicle itself, the electric powertrain, the high-voltage circuit, the Rechargeable Electrical Energy Storage System or REESS, battery installation and protection, and the behavior of the overall system under normal conditions, fault conditions, and certain accident conditions. Standards and technical regulations define specific requirements and evaluation methods for these hazards so that product safety performance can be assessed against technical criteria.
Is an Electric Vehicle Completely Different From a Gasoline Vehicle in Terms of Safety?
No. A large part of the fundamental principles of vehicle safety remains the same. An electric vehicle must also be evaluated for areas such as braking, steering, field of vision, occupant protection, seats, seat belts, and many other requirements. The difference is that the electric powertrain introduces additional hazards and Failure Modes that either do not exist in vehicles equipped with internal combustion engines or occur in a different form.
For example, a significant amount of energy is stored in the battery pack of an electric vehicle, and parts of the system operate at high voltage. Under defined conditions, the driver, occupants, and other persons must not be exposed to hazardous contact with live parts. In the event of a fault or damage, the design must also meet the relevant protective requirements. In addition, the battery or REESS must demonstrate acceptable behavior under a range of mechanical, electrical, and thermal stresses defined by the applicable requirements. EV Safety is therefore better understood as an additional layer on top of general vehicle safety requirements, rather than a replacement for them.
Why Does the High-Voltage System Require Separate Safety Requirements?
One of the fundamental differences in an electric vehicle is the presence of a High Voltage System. High voltage has a specific technical definition in the relevant regulations, and components such as the traction battery, high-voltage cables, inverter, electric motor, and related equipment may form part of this system. The primary objective of safe design is to prevent people from being exposed to hazardous contact with live parts under defined conditions and to prevent insulation failure or system damage from leading to uncontrolled electrical hazards.
For this reason, concepts such as protection against direct and indirect contact, insulation resistance, protection of high-voltage components, appropriate electrical connection of conductive parts, and system condition monitoring are addressed in electric vehicle safety requirements. UN Regulation No. 100, or UN R100, is one of the important regulations in this field and covers requirements related to vehicles equipped with electric powertrains and rechargeable electrical energy storage systems within its scope of application.
What Is REESS and Why Is It Important for Electric Vehicle Safety?
The term REESS frequently appears in electric vehicle regulations and stands for Rechargeable Electrical Energy Storage System. In many electric vehicles, the traction battery pack is the main part of this system, but using the term REESS helps ensure that the requirements are not limited to one specific battery technology or architecture.
A REESS stores a significant amount of energy and must demonstrate acceptable safety behavior under different conditions. This is not determined solely by battery cell quality; Pack design, electrical connections, thermal management, mechanical protection, the battery management system, and the way the assembly is installed in the vehicle can all affect the final outcome. Therefore, safety cannot be assessed simply by examining cell specifications or battery capacity and then drawing conclusions about the entire system. UN R100 also establishes specific conditions and criteria for evaluating REESS within the scope of its relevant requirements.
What Hazards Is an Electric Vehicle Battery Evaluated Against?
A vehicle battery does not experience only one constant condition throughout its service life. Vibrations caused by vehicle movement, temperature variations, mechanical loads, charging and discharging, the possibility of short circuits, and abnormal system conditions can all place stress on the battery. For this reason, REESS safety evaluation covers a range of different scenarios, and the applicable tests and acceptance criteria must be determined from the referenced regulation or standard.
The purpose of these evaluations is not necessarily to require the battery to remain undamaged under every unlimited condition; the regulation or standard defines the test conditions and acceptable criteria. This distinction is important because terms such as “fireproof battery” or “completely safe in a crash” are too broad from an engineering perspective. A more technically meaningful question is: Under which standardized conditions has the system been evaluated, and which criteria has it met?
What Is Thermal Runaway and Why Is It Discussed So Often?
One of the important topics in lithium-ion battery safety is Thermal Runaway. Under certain conditions, an increase in the temperature of a cell can trigger reactions that generate additional heat and make the cell temperature increasingly difficult to control. If this event or its effects spread from one cell to adjacent cells, Thermal Propagation also becomes a concern.
In battery system design, the objective is not limited to reducing the likelihood of such an event starting; detecting abnormal conditions, thermal management, Pack design, and measures that reduce the likelihood or consequences of thermal propagation are also important. Thermal Runaway and Thermal Propagation are important areas of battery safety development, and requirements relating to the thermal behavior of REESS continue to evolve alongside technology and regulations.
This illustrates that electric vehicle regulations do not remain static. As industry experience grows, technology develops, and requirements change, evaluation methods and criteria may also be revised. Therefore, in a real project, the applicable version and Series of Amendments of the relevant regulation must be identified; simply stating “compliant with R100” is not sufficient.
What Role Does Battery Thermal Management Play in Safety?
Temperature can affect the performance, service life, and safety of a vehicle battery. The thermal management system is designed to control the thermal conditions of the cells and Pack within the intended ranges and is an important part of the battery and energy-system architecture in electric vehicles.
However, thermal management is not simply about cooling the battery in hot weather. Depending on the vehicle design, the system must be capable of managing the thermal condition of the assembly under different operating conditions, and temperature data may also serve as one of the inputs to the battery management system. Poor performance in this area can affect available power, charging, battery life, and, under severe conditions, system safety. Thermal design and battery control strategies should therefore be considered together with the electrical and mechanical design of the assembly.
What Happens to the High-Voltage System in a Crash?
Electric vehicle safety does not end with crash prevention. If a collision occurs, the condition of the electrical system must be considered in addition to conventional occupant protection. Damage to the battery or high-voltage components can create hazards such as contact with live parts, mechanical damage to the battery, and, under certain conditions, thermal or fire hazards. The condition of the high-voltage system and energy storage assembly after a collision is therefore an important aspect of electric vehicle safety.
Regulations relating to crash safety for vehicles equipped with electric powertrains may include post-crash electrical safety criteria in addition to structural requirements. For example, UN Regulation No. 153 covers fuel system integrity and electric powertrain safety in rear-end collisions within its scope of application. This again demonstrates that EV Safety is not a single test; a combination of vehicle, electrical-system, and energy-storage requirements must be considered together.
Is an Electric Vehicle Fire Different From a Combustion Vehicle Fire?
Both types of vehicles can catch fire under various conditions, but the nature of stored energy and the management of certain incidents are not the same. In a damaged lithium-ion battery, temperature rise, gas release, and the possibility of certain thermal reactions occurring or reoccurring can affect how an incident is managed. For this reason, emergency response procedures and vehicle-specific information for first responders are important.
However, differences in the nature of the hazards should not lead to broad conclusions such as “electric vehicles are inherently more likely to catch fire.” Comparing fire risk across different technologies requires data, a precise definition of the type of incident, the technology involved, and operating conditions. From an engineering perspective, the objective is to identify the specific hazards associated with each technology and establish appropriate measures and requirements for their prevention, control, and management.
Charging Is Also Part of Electrical Safety
An electric vehicle spends part of its time connected to an external energy source, so safety is not limited to driving conditions. The vehicle’s connection to charging equipment, power transfer, connector condition, temperature control, and system behavior under fault conditions must also be considered in safe design. Depending on the system, charging type, and market, applicable regulations and standards may define different requirements for this area.
This also demonstrates why EV safety should be evaluated at the system level. A battery that meets its own relevant requirements does not, by itself, guarantee the safety of the complete vehicle if it is integrated with an unsuitable charging system, cable, connector, or electronic control system. Just as the performance of a single component does not determine the safety of an entire combustion-engine vehicle, the interaction between components is also critical in an electric vehicle.
What Role Does the BMS Play in Battery Safety?
The Battery Management System, or BMS, is one of the key components of the battery system. The BMS monitors information such as voltage, current, and temperature and, depending on the system architecture, can play a role in managing charging and discharging, protecting the battery, and detecting abnormal conditions. Battery safety is therefore not solely the result of mechanical Pack design or appropriate cell selection; electronic and software layers also play a role in system control.
This is one of the important differences between modern vehicles and the traditional approach to vehicle testing. Part of a product’s safety behavior now depends on algorithms, sensors, and control-system decisions, and a software change can affect system performance under certain conditions. Therefore, when defining a product Configuration for evaluation, the relevant hardware and software versions may also be important.
What Is UN R100?
UN Regulation No. 100 is one of the most important international regulations related to the safety of vehicles equipped with electric powertrains. This Regulation covers requirements related to the Electric Power Train and REESS within its scope of application and has evolved over time through regulatory amendments.
Therefore, in a real project, the term “R100” alone does not provide enough information for test planning or evaluation. It is necessary to determine which Series of Amendments, which version, and which part of the regulation apply to the vehicle or REESS in question. If you are unfamiliar with the naming structure of UN Regulations and the differences between the terms UNECE, ECE, and UN, the TAT Knowledge Base article “What Is UNECE? The Relationship Between UN Regulations and Vehicle Standards in Iran” explains this topic in greater detail.
What Is the Status of Electric Vehicle Standards in Iran?
As new technologies enter the automotive industry, requirements related to electric vehicles have also become increasingly important within the broader set of vehicle standards. Vehicle requirements in Iran also include areas related to electrical safety and new powertrain technologies. However, the same principle that applies to other vehicle standards applies here as well: the presence of a standard on a list is not, by itself, sufficient to determine its Applicability or implementation status.
The vehicle category, powertrain type, system characteristics, and scope of the standard must be reviewed, while the status and timing of implementation of the requirement are also important. To review related standards and their implementation status, you can use the Table of 122 Vehicle Standards on the TAT website. This is particularly important for projects involving products that are expected to enter the market in the future, because the development plan should also consider the requirements applicable when the product enters the approval or market introduction process.
Does Battery Safety Mean Electric Vehicle Safety?
No. The two concepts are closely related, but they are not the same. A Battery Pack may successfully complete a series of tests relevant to the battery itself, but the vehicle must still be evaluated for battery installation, mechanical protection, high-voltage architecture, control systems, charging, crash behavior, and other applicable requirements. At the same time, the vehicle must continue to meet general safety requirements relating to braking, steering, visibility, seats, and occupant protection.
For this reason, electric vehicle safety is better understood as a multilayered concept: cell and battery-component safety, REESS safety, high-voltage system safety, integration of these systems into the vehicle, and ultimately the safety of the vehicle as a complete product. A weakness at any layer can affect the performance of the overall system, and the successful performance of one component in a particular test should not be generalized to the entire vehicle without considering the scope of the result.
Are Hybrid Vehicles Also Subject to Electrical Safety Requirements?
Depending on the vehicle architecture and the scope of the applicable regulation, yes. In the context of technical requirements, “electrified” vehicles are not limited to Battery Electric Vehicles or BEVs. Hybrid and Plug-in Hybrid vehicles also contain electrical components and energy storage systems and, depending on their technical characteristics, may be subject to requirements relating to electric powertrains.
For this reason, applicable standards should not be determined solely from commercial labels such as “hybrid” or “electric.” The actual system architecture, operating voltage, type of energy storage, interconnection of components, and scope of the standard are what determine applicability. This follows the same logic used for other vehicle standards: first define the product and its exact Configuration, then assess the Applicability of the relevant requirements.
Electric Vehicle Safety Starts at the Design Stage, Not at the Final Test
Many electric vehicle safety requirements cannot be resolved with a minor change after the final prototype has already been built. Battery location, mechanical protection of the Pack, high-voltage cable routing, system connection and disconnection architecture, thermal management, BMS, and the interaction between electrical systems and the vehicle structure are all decisions that begin taking shape during the early stages of design.
For this reason, applicable requirements should be identified before the product architecture is finalized. If the development team discovers a fundamental Requirement only when preparing the specimen for testing, addressing it may require changes to the mechanical, electrical, or software design. New projects should also consider relevant regulatory developments and the planned timing of market introduction in addition to requirements currently in force.
Electric Vehicle Safety Is Not a Test; It Is a System
The question “How is an electric vehicle tested for safety?” does not have a short answer because EV safety is not the result of a single test or even a single standard. The high-voltage system must provide protection against hazardous contact, the REESS must demonstrate acceptable behavior under defined conditions, thermal management and control systems must manage abnormal conditions, and the battery assembly must be integrated into the vehicle in a way that controls electrical and thermal hazards under defined operating and accident conditions. Alongside all of these requirements, the vehicle must still meet the general safety requirements applicable to a motor vehicle.
Therefore, for an electric vehicle project, the right question is not simply “What tests does the battery require?” A more precise question is: What hazards exist at the battery, electrical-system, and vehicle levels; which standards apply to the specific Configuration; and what evaluations are required to demonstrate conformity with each requirement? The answers to these questions form the actual safety and testing program for an electric vehicle.