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ASTTBC RFPT — Emergency Lighting (EM) · Question

When inspecting nickel-cadmium (Ni-Cd) batteries in an emergency lighting unit, which of the following is a physical sign of 'thermal runaway' or excessive charging temperature?

Thermal runaway in sealed Ni-Cd batteries often leads to overheating, causing the plastic casing to soften, bulge, or leak due to internal pressure and heat.

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Question: When inspecting nickel-cadmium (Ni-Cd) batteries in an emergency lighting unit, which of the following is a physical sign of 'thermal runaway' or excessive charging temperature?

Answer options: ✅ Distorted or bulging battery casing

  • Blue crystal formation on terminals
  • Light brown electrolyte discoloration
  • Increased specific gravity in one cell

Correct answer: Distorted or bulging battery casing

Explanation: Thermal runaway in sealed Ni-Cd batteries often leads to overheating, causing the plastic casing to soften, bulge, or leak due to internal pressure and heat.

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