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Difficulty: MediumFire Safety and Classification

A technician is using a bench grinder to deburr a custom magnesium wheel rim when friction sparks ignite a pile of fine metal dust beneath the machine. Which extinguishing agent is required to safely suppress this fire?

  1. A
    Pressurized water stream
  2. B
    Carbon dioxide gas
  3. Specialized Class D dry powderAnswer
  4. D
    Aqueous film-forming foam

Answer

Specialized Class D dry powder
Combustible metals such as magnesium, titanium, and sodium are categorized under Class D fires. These fires burn at extremely high temperatures and require specialized Class D dry powder extinguishing agents (such as granulated sodium chloride or copper-based powders) that smother the fuel and absorb heat without triggering violent chemical reactions.

Step-by-Step Solution

1
Identify the fuel source and its corresponding fire classification.
Magnesium dust is a combustible metal, which categorizes this emergency as a Class D fire.
Fire extinguishing agents must be strictly matched to the specific chemical properties of the burning material to avoid dangerous reactions.
2
Select the appropriate extinguishing agent formulated for combustible metals.
A Class D dry powder extinguishing agent must be used.
Class D agents form a smothering crust over the burning metal to cut off oxygen and dissipate heat safely, whereas water-based or gaseous agents react violently with or fail to suppress burning reactive metals.

Key Concept

Combustible metal fire extinguishing requirements (Class D fires)
Estimated Time:1m 0s
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Topics

Fire Safety and Classification

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