What is typically insufficient energy to ignite most higher density combustibles?

A simple arc is considered typically insufficient energy to ignite most higher density combustibles because higher density materials often require a greater amount of energy to reach their ignition temperature. Arc energy, while capable of creating heat, often does not produce the sustained temperature necessary for ignition in materials with a higher ignition threshold.

In contrast, higher energy sources such as high-temperature flames or certain exothermic chemical reactions can provide enough heat to overcome the ignition barrier that these dense materials present. A spark from a lighter, while it might ignite more easily ignitable materials, usually does not deliver enough energy for ignition in denser combustibles either. Therefore, a simple arc falls short of what's needed to effectively ignite these types of materials.