Tempered safety glass starts as ordinary glass, then runs through a furnace and a rapid cooling blast that puts its surfaces under compression. The result is several times stronger than untreated glass and, when it does fail, it breaks into small dull pieces instead of long shards. Every shower enclosure Accurate Glass & Mirror builds in Bergen County uses it.
Tempered glass carries a permanent mark, usually a small etched or ceramic logo in one corner naming the fabricator and the safety standard the lite was made to. It sits deliberately where a frame or a wall would normally hide it, and on a frameless shower door it often lands low on a vertical edge. If a panel in a hazardous location has no mark at all, that is worth asking about. Inspectors look for it, and so should anyone buying a used or salvaged panel.
There is a second family of safety glazing worth knowing. Laminated glass holds together on a plastic interlayer instead of crumbling, and it satisfies safety glazing requirements in most residential locations too. The two behave completely differently at the moment they break.
The compressed skin is what makes this glass strong, and an edge chip or a corner nick breaks that skin. Damage there can sit quietly for weeks and then let go with no impact at the moment it happens, which is where the stories about doors exploding on their own come from. Handle panels on the long edge, never set glass down on a hard corner, and keep tile trowels and shower caddies away from exposed edges. It is also why cutting, drilling and polishing all happen first. Once glass has been through the furnace it cannot be cut, notched or drilled without destroying it.
New Jersey follows model building codes calling for safety glazing where a person can fall into glass or where glass meets water: shower and tub enclosures, doors and the glass beside them, low panels, and stair and railing glass among them. Railings carry load and height requirements of their own on top of that. Rather than quoting a section number at anybody, confirm the requirement for a specific opening with your local building department, since towns run and interpret their own inspections. Replacement work is where this gets overlooked most often, because an older enclosure may well predate the requirement it sits under today.
No. Any hole, notch or hinge cutout has to be made while the glass is still annealed, before it goes into the furnace. Drilling afterward releases the stress locked in the sheet and it comes apart on the spot. A towel bar added later gets mounted to the wall instead, or the panel is remade with the opening in it.
Those are normal artifacts of the process. Glass rides through the furnace on rollers at high heat, which can leave a subtle waviness, and the pattern from the cooling nozzles can appear as faint iridescent marks in certain light or through polarized sunglasses. Neither affects strength, and both are accepted characteristics of heat-treated glass.
Forty years of setting glass in North Jersey homes means the questions about strength, breakage and code come up weekly, and there is a real answer to each one. Call the Lodi shop at (201) 460-1313, or come see full enclosures standing on the floor.
