Chapter 5 - Mechanical Energy and Vehicle Anatomy

Knowledge Objectives (What you must know)

Mechanical Energy & Injury

  • Energy is the capacity to do work and cannot be created or destroyed — only transformed

  • Mechanical energy consists of:

    • Kinetic energy (motion)

    • Potential energy (position)

  • Kinetic energy depends on:

    • Vehicle mass (weight)

    • Speed (velocity)

  • Potential energy is stored due to position

  • Work is the transfer of energy causing displacement:

    • Positive work (with direction of travel)

    • Negative work (against direction of travel)

  • The law of conservation of energy applies to vehicle crashes — energy changes form and transfers during impact

Mechanism of Injury (MOI)

  • MOI describes how energy transfer causes injury to the body

  • Understanding MOI helps:

    • Predict injury patterns

    • Guide patient assessment

Three Collisions in Every Crash

  1. Vehicle impacts object

    • Damage severity correlates with energy release and MOI

  2. Occupant impacts interior

    • Seat belts and airbags reduce but do not eliminate injury

  3. Internal organs impact body structures

    • Causes compression, shearing, and tearing injuries

Collision Classifications

  • Front (head-on)

  • Rear-end

  • Lateral (side/T-bone)

  • Rollovers

  • Rotational

Key injury patterns

  • Rear-end → whiplash (head restraints reduce injury)

  • Lateral → high fatality risk; cervical spine vulnerable

  • Rollover → ejection is life-threatening

  • Rotational → often multiple impacts

Vehicle Frame Systems

  • Body-over-frame — separate ladder-style frame

  • Unibody (unitized) — frame and body merged; uses crumple zones

  • Space frame — tubular skeleton with nonstructural panels

Structural Components (Front to Rear)

  • Bumper system

  • Core/radiator support

  • Upper rails (crumple zones)

  • Strut towers

  • Engine cradle (designed to shear/drop)

  • Cowl section

  • Firewall (bulkhead)

  • Dash reinforcement bar

  • Rocker panels

  • Roof posts (A, B, C)

Doors & Side Structures

  • Hinges — often hardened steel

  • Door limiting device (swing bar) — controls opening

  • Impact beam — high-strength member; very difficult to cut

Roof Posts (Pillars)

  • A-post — windshield area; may contain reinforcements

  • B-post — between doors; often houses seat belts, pretensioners, SRS

  • C-post — rear structural support

Supplemental Restraint Systems (SRS)

  • Seat belts (three-point systems)

  • Pretensioners — pyrotechnic tightening devices

  • Airbags — deploy with heat and force

Piston Struts

  • Found in hoods, hatchbacks, liftgates

  • Contain pressurized gas/fluid

Vehicle Construction Materials

  • Metals:

    • Ferrous

    • Nonferrous

    • Advanced alloys

  • Advanced steels:

    • HSS/AHSS

    • Boron-alloyed steel

  • Aluminum alloys

  • Magnesium alloys

  • Carbon fiber reinforced polymer (CFRP)

Federal Safety Standards

  • FMVSS establish minimum vehicle safety performance

  • Designed to reduce injury and death

Vehicle Glass Types

  • Laminated safety glass (LSG) — windshields

  • Tempered safety glass (TSG) — side/rear glass

  • Polycarbonate — strong plastic glazing

  • Ballistic glass — multilayer protective glass

Vehicle Classifications

DOT classifies vehicles by:

  • Passenger vs non-passenger

  • Cargo volume

  • Gross Vehicle Weight Rating (GVWR)

Includes:

  • Cars

  • Trucks

  • Vans

  • SUVs

  • Specialty vehicles

Vehicle Identification Numbers (VIN)

  • 17-character code

  • Excludes I, O, Q

  • Identifies:

    • Manufacturer

    • Vehicle type

    • Country of origin

    • Model year

Vehicle Propulsion Systems

  • Conventional ICE (gasoline/diesel, 12-V systems)

  • Hybrid electric vehicles (HEV)

  • Hydrogen fuel-cell vehicles

  • Electric vehicles (EV)

Definitions (Term — Definition)

  • Kinetic energy — Energy of motion

  • Potential energy — Stored energy due to position

  • Work — Transfer of energy causing movement

  • MOI — Mechanism describing injury from energy transfer

  • Unibody — Integrated body/frame vehicle construction

  • SRS — Supplemental restraint system (airbags, pretensioners)

  • FMVSS — Federal Motor Vehicle Safety Standards

  • GVWR — Maximum safe operating weight of a vehicle

  • VIN — Unique 17-character vehicle identifier

NFPA / Test Facts (If X → then Y)

  • If vehicle speed or mass increases → kinetic energy increases

  • If energy transfer exceeds tissue tolerance → injury occurs

  • If interior damage is severe → expect serious internal injuries

  • If lateral collision occurs → cervical spine risk is high

  • If rollover occurs → ejection risk is life-threatening

  • If unibody construction is present → energy is redirected via crumple zones

  • If impact beam is cut → tool resistance will be extreme

  • If boron or AHSS is encountered → cutting difficulty increases

  • If CFRP is cut → airborne particulates are created

  • If SRS components are undeployed → blast/burn risk exists

Safety Awareness (Explicit from text)

  • Injury occurs when energy transfer exceeds tissue tolerance

  • Exterior and interior damage are critical for predicting patient injuries

  • Cutting near reinforced structural members may cause collapse

  • Always expose and check roof posts and rails for SRS components before cutting

  • Never cut piston struts — explosion/impalement risk

  • CFRP cutting requires respiratory protection

  • Glass management protects rescuers and patients

  • HEV systems include electric motor, generator, ICE, and battery pack