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Sheet A-106
PPDPDD CE

Glassconcept

Glazing types: annealed, tempered, heat-strengthened, laminated, wired, spandrel

One-line orientation

Glazing types differ mainly in strength and break behavior, and the high-yield traps are that tempered and laminated are both “safety” glass (but break differently) while heat-strengthened is not safety glass.

Key points

  • Annealed: cooled slowly so internal stresses release; standard glass that breaks into large, sharp shards. Not safety glazing.
  • Tempered: heated then rapidly cooled; much stronger than annealed and shatters into small cubes → qualifies as safety glazing. Cannot be cut/drilled after tempering.
  • Heat-strengthened: heating/cooling cycles make it stronger than annealed but less than tempered — and it is NOT a safety glazing.
  • Laminated (safety glass): two lites bonded by an interlayer (PVB resin) that holds fragments together when broken → safety + security + acoustic benefits; can stay in the frame after impact.
  • Wired glass: embedded wire mesh to hold pieces together / resist shattering (historically associated with fire-rated openings). Traditional wired glass is not automatically impact-safety glazing; modern fire-rated safety glazing must satisfy the relevant impact requirement.
  • Patterned / obscure glass: surface pattern rolled in, or sand-blasted / acid-etched, for privacy/vision obscurity.
  • Spandrel glass: opaque glazing in curtain walls used to conceal structure (slabs, columns, mechanical zones) between vision areas.

Break pattern — not strength — decides safety glazing

Two of these four qualify as safety glass. How the pane breaks settles it, not how strong it is.

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Safety glazing is decided by break pattern, not by strength Four glass panes in a row, each drawn with the fracture pattern it actually makes, so the break pattern — not the strength — decides which count as safety glazing. Panes one to three sit over a quiet weaker-to-stronger relative-strength scale with aligned ticks; the fourth, laminated, is set apart off the scale because its strength depends on the glass used. Annealed breaks into a few large sharp shards; cooled slowly, baseline strength; it sits outside the safety bracket. Heat-strengthened breaks into larger irregular fragments; stronger than annealed; it also sits outside the bracket, and an amber caution says it is still not safety glazing. Tempered breaks into a field of small uniform blunt cubes; much stronger. Laminated shows a continuous cracked web held in the pane. An ink-blue bracket labeled safety glazing spans only the tempered and laminated panes. A distinct assembly-section inset below laminated shows three directly labeled layers: glass, PVB, glass. As strength increases left to right the verdicts refuse to follow — no, no, yes — and laminated qualifies off the scale, because qualification is keyed to how the glass breaks, not how strong it is. RELATIVE STRENGTHWeakerStrongerSAFETY GLAZINGAnnealedlarge sharp shardscooled slowly · baselineHeat-strengthenedlarger fragmentsheat/cool cycles · strongerTemperedsmall blunt cubesrapidly cooled · much strongerLaminatedcracks but heldPVB-bonded · strength variesStronger than annealed; still not safetyASSEMBLY SECTIONGlassPVBGlass

Confusions / comparison

TypeHow it’s madeRelative strengthBreak behaviorSafety glazing?
AnnealedCooled slowlyBaselineLarge, sharp shardsNo
Heat-strengthenedHeat/cool cyclesStronger than annealedLarger fragmentsNo
TemperedHeated, rapidly cooledMuch strongerSmall cubesYes
LaminatedLites bonded by PVB interlayerDepends on glass usedCracks but held togetherYes
WiredEmbedded wire meshLow (wire holds pieces)Held by wireFire-related; not automatically impact-safety glazing
SpandrelOpaque coating/backingn/a (concealment, not strength)n/an/a (conceals structure)

→ Flat glass production (this topic): sheet / plate / float — how the base glass is formed before processing · (Cross-module) Code: safety-glazing / hazardous-location requirements · (Cross-module) Systems: glazing thermal/acoustic performance.

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Related units

Flat glass production