When fires break out, materials often produce large amounts of heavy smoke and toxic gases that put people at risk.
Toxic gas is generally scary but is even more frightening during a fire. Threats include everything from VOCs (chemicals with low water solubility) and carbon dioxide to chloride, particulates, and more.
Meanwhile, smoke can quickly fill rooms and tight spaces, irritating the lungs and eyes, stealing oxygen, and impairing movement. As the dense black smoke spreads, visibility drops, making escape harder.
Every building with electricity has wiring carrying power to electronics, lights, and machinery.
But what happens when the wiring fails?
Let’s say a fire breaks out in an area with halogen-containing PVC wires. Burning PVC creates hydrogen fluoride and hydrogen chloride gas. When hydrogen chloride gas mixes with water, it becomes hydrochloric acid (HCl).
If you’re unfamiliar with this particular acid, it causes burns and irritation to a person’s skin, eyes, and lungs. It can also damage sensitive electronic parts, potentially ruining them.
Recently, manufacturers have found themselves striving to develop safer alternatives to insulations like polyvinyl chloride (PVC), nylon, and HDPE.
While these common insulations are still widely available, manufacturers are developing less harmful “low smoke zero halogen” (LSZH) ones. As this insulation burns, it produces little smoke and no halogens.
The result is a less dangerous cable, buying people more time to escape during a fire.
So, what makes halogens so dangerous?
If you’re unfamiliar with halogens, you can find them conveniently housed in Group 17 of the periodic table. Its members include chlorine, which treats water; and iodine, used as an antiseptic. Others in the group, like bromine, fluorine, astatine, and tennessine, have applications throughout manufacturing, including plastic and pharmaceutical production.
Halogens are highly reactive, too, reacting with all kinds of metals and non-metals. For example, chlorine reacts with hydrogen to make hydrogen chloride, a toxic gas causing burns, blindness, and lung damage.
When low smoke zero halogen cable jackets burn, the resulting smoke isn’t as dangerous.
Low smoke zero halogen has several names, including LSZH, LSOH, LS0H, or LSHF, depending on the manufacturer.
Tray cables commonly use LSZH jackets to protect conductors used in buildings, schools, hospitals, and other public places. But earning the LSZH designation is no easy feat. Wire and cable products must meet several UL standards for flammability, including VW-1, flame spread, and smoke density.
Despite being more expensive than other wiring options, LSZH products are much safer thanks to stringent tests.
UL 1685 is a flame test performed on groups of cables, including tray cables, to test flame propagation. A tester hangs the tray cable inside a steel ladder tray and applies a flame toward the bottom of it for 20 minutes. The jacket passes if the fire spread is less than the eight-foot threshold.
Earning the LSZH designation is no easy feat. Wire and cable products must meet several UL standards, including flammability, flame spread, and smoke density.
Despite being more expensive than other wiring options, LSZH products’ stringent testing makes them much safer.
UL 1581 and the VW-1 Vertical Flame Test determine a cable’s fire resistance and smoke emissions. During this process, testers apply fire conditions to measure how much smoke the cable produces when it burns and how far it spreads.
This test is similar to the UL 1581 test but specifically for communication cables.
UL 2556 tests for fire spread and smoke density but includes tensile strength, flexibility, and high-temperature tests, too.
This is the gold standard test for tray cable products installed in cable trays, testing several key features.
Cables undergoing UL 1277 testing must show limited flame spread on the cable, high strength, and proper conductor insulation. The standard applies to cables 600V or higher, with certain wire types qualifying for a dual rating.
Additional tests include operating temperature, weather, moisture, environmental resistance, and ampacity.
This smoke density test measures the amount of smoke a cable creates as it burns.
Also called an optical density test, light sources help measure how thick the burning smoke is. For a cable to pass and earn the “low smoke” designation, the density can’t surpass a specific threshold.
Other testing sometimes occurs concurrently with this one, including ones covering smoke toxicity.
NFPA 262 is a standard applied to flame movement and smoke generation for LSZH cables.
Specifically, this test measures flame propagation – how far flames move – and smoke production in air-handling spaces. Air-handling spaces are areas in a building used to circulate air and include plenum spaces in the ceiling and floor, compartments, and shafts.
It seems like a lot of different standards, but they combine to ensure every LSZH cable lives up to its name.
From general wiring and lighting to power and tray cable installations, LSZH cable has a wide array of uses.
But the most common places where you’ll find LSZH cable used is anywhere people are, including:
In an emergency, LSZH is much less dangerous than standard PVC cables, which throw off toxic black smoke as they burn. During an emergency, lower smoke density can save lives. First responders rushing toward the fire have better visibility, while those leaving the emergency can escape faster.
Long story short, less flammable wire and cable saves lives. And as safety measures improve, we’ll see LSZH products find even more applications.
Innovation isn’t linear – it takes years for groundbreaking solutions to reach the market and gain mass approval.
Surprisingly, that is exactly where the industry finds itself when discussing low smoke zero halogen products. Safety standards are improving every year, making LSZH products more commonplace in buildings throughout the United States. Building codes are reflecting the industry, often mandating LSZH cables in areas where people or expensive equipment are.
Manufacturers are also doing their part to get more LSZH products in use. Forward-thinking companies are constantly finding ways to produce safer, less expensive products, lowering the barrier to entry.
Finally, safer products are better for the environment. Because they don’t contain halogens, LSZH materials are easier to recycle compared to PVC. The result is less garbage ending up in landfills. Wires and conduits made from low smoke zero halogen materials also pose less of an environmental risk while burning.
Although we can’t prevent fires from happening, manufacturers, installers, and code enforcement officials can make life safer for everyone.
