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CDL · Communication Rules

When are hazardous materials placards required on a vehicle?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

When transporting certain hazardous materials at or above threshold quantities, to warn others and inform emergency responders of the hazard class

  1. A When transporting certain hazardous materials at or above threshold quantities, to warn others and inform emergency responders of the hazard class
  2. B Never
  3. C Only on weekends
  4. D Only at night

Why this is the answer

HAZMAT PLACARDS are required when transporting certain hazardous materials at or above THRESHOLD QUANTITIES (some materials require placards in ANY amount — Table 1 materials; others only above 1,001 lbs aggregate — Table 2). CDL hazmat endorsement. Placards are diamond-shaped signs on ALL FOUR SIDES of the vehicle that identify the HAZARD CLASS by color, symbol, and number — warning the public and informing emergency responders what they're dealing with in an accident/spill. The shipper provides placarding info; the driver ensures correct placarding. Knowing when placards are required (threshold quantities; some materials always) is core hazmat knowledge.
Source: FMCSA CDL Manual — Hazmat, Placarding Requirements

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About this topic: Communication Rules

Communication rules cover shipping papers, placards, labels and markings: what each must show, where papers must be kept in the cab, and when placards are required. This is the most heavily tested hazmat topic. This is one of 19 Hazardous Materials questions on communication rules, each with a full explanation on a single study page.

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