Final answer:
The assertion that it is unsafe to work under a vehicle supported only by jack stands is true. This practice is hazardous as jack stands may not provide adequate stability; additional safety measures are required to prevent accidents.
Step-by-step explanation:
It is unsafe to work under a vehicle supported only by jack stands. The assertion is True. When working under a vehicle, it is crucial to use a combination of jack stands and wheel chocks, and ideally, a hydraulic lift or a professional-grade lift system. Jack stands alone may not provide the necessary stability or security, and there is a risk of the vehicle slipping or the stands failing, which can lead to serious injury or death.
It is a standard safety practice to use additional support mechanisms to ensure that the vehicle remains securely elevated while work is being performed underneath it. For added security, many mechanics will also place the removed tire beneath the car's side as an extra safety precaution in case the jack stands fail.
In summary, when it comes to vehicle maintenance safety, relying only on jack stands is considered hazardous. Appropriate safety measures must always be observed to protect oneself from potential accidents.