CDL · Liquid Surge

What is the difference between BAFFLES and BULKHEADS in a liquid tanker, and how does each affect surge?

Correct answer

BAFFLES are internal panels with holes that allow liquid to pass through slowly, reducing front-to-back surge but not side-to-side; BULKHEADS are solid dividers that completely separate compartments, eliminating surge within each compartment entirely

  1. A Baffles are only used in food-grade tankers
  2. B Baffles are external guards; bulkheads are decorative panels
  3. C They are the same thing with different names
  4. D BAFFLES are internal panels with holes that allow liquid to pass through slowly, reducing front-to-back surge but not side-to-side; BULKHEADS are solid dividers that completely separate compartments, eliminating surge within each compartment entirely

Why this is the answer

BAFFLES and BULKHEADS serve different surge-control functions and produce different handling characteristics:

Baffles: Perforated or slotted internal partitions that span the cross-section of the tank; liquid can flow through the openings, but the restricted flow DAMPENS front-to-back (longitudinal) surge; the liquid cannot surge as freely during braking and acceleration; baffles do NOT prevent side-to-side (lateral) surge — they have limited effect on handling in turns; a baffled tanker is better for straight-line braking but still susceptible to rollover in turns due to lateral surge.

Bulkheads: Solid, impermeable dividers that create completely separate compartments; liquid CANNOT flow between compartments; surge within each compartment is limited by its size — a smaller volume surges less; bulkhead tanks can carry different products in different compartments.

Unbaffled tanks: Some tanks (particularly smooth-bore tanks for certain food-grade products) have NO internal divisions — these have the most severe surge characteristics and require the most conservative driving.

Practical implication: Even a baffled tanker requires significantly more braking distance than a solid-load vehicle of the same weight; the surge forward during hard braking can actually accelerate the vehicle briefly before braking takes effect — this is the 'wave effect' that makes tanker driving different from other CMV driving.

Source: FMCSA CDL Manual, Chapter 10, Tank Vehicles, Baffles and Bulkheads

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all Liquid Surge and other topics.

Take the Tanker practice test →

About this topic: Liquid Surge

Liquid surge is the forward-and-back movement of a partially filled tank, strong enough to push a stopped truck into an intersection. These questions cover why it happens, how baffles and bulkheads limit it, and how to brake and stop to control it. This is one of 10 Tanker questions on liquid surge, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.