In the field of electrical engineering standards, a debate has long been settled. The question is no longer whether low-smoke halogen-free (LSZH) cables are safer than PVC cables, but rather: in which scenarios is the use of LSZH cables mandatory?

For many years, construction companies have preferred PVC (polyvinyl chloride) cables because they are cheaper and more flexible. However, with the continuous development of fire safety engineering and the increasingly stringent requirements for "safe evacuation routes" in regulations worldwide, things have fundamentally changed. Low-smoke halogen-free materials have gone from being a "plus for green building" to a legally mandated, non-negotiable requirement in specific application scenarios.

Below, we will systematically clarify: in which situations must you—or rather, legally should—prioritize the use of low-smoke halogen-free cables?

I. First, clarify: what is true "low-smoke halogen-free"?

Before discussing "when to use," we need a clear definition of the product itself. A true low-smoke halogen-free cable (sometimes written as LSOH, 0HLS, or ZHLS) must meet the following core performance indicators in a fire:

Low Smoke Performance (according to IEC 61034-2): Ensures visibility. During a fire, the smoke concentration produced by the burning cable must be sufficiently low to allow personnel to clearly see safety exit signs and for firefighters to easily identify the fire source and rescue routes.

Halogen-Free (according to IEC 60754-1/2): Ensures non-toxicity and non-corrosiveness. The gases produced during combustion must not contain halogen acid gases (such as hydrogen chloride). PVC cables release hydrochloric acid gas when burning; this reacts with water to form hydrochloric acid, which severely corrodes electronic equipment and metal structures, and seriously damages the respiratory tract.

Low Corrosion (according to IEC 60754-2): Protects equipment. Even if it does not fully meet the zero-halogen requirement, its corrosiveness must be controlled within an extremely low range.

Flame Retardancy (according to IEC 60332-1 or IEC 60332-3 series): Does not easily ignite spontaneously and can prevent the spread of flames. In short: When PVC cables burn, you face "black smoke + hydrochloric acid + suffocation"; while when LSZH cables burn, you face "a small amount of white smoke + slight irritation + escape."

II. Six Typical Scenarios Where Low-Smoke Halogen-Free Cables Must Be Used

The following scenario assessments are primarily based on relevant chapters of the EU Building Product Regulation (CPR), UK BS 5839-1 (Fire Detection and Alarm Systems Standard), BS 6701 (Communication Cable Installation Standard), IEC 60332 series from the International Electrotechnical Commission, and the US NEC (National Electrical Code). While there may be slight differences in details across countries and regions, the basic logic remains highly consistent.

1. Densely Populated Public Places with Difficult Evacuation
Typical places include large shopping malls, theaters, stadiums, train stations, airport terminals, and public corridors of high-rise office buildings. These areas have extremely high population density, and many people are unfamiliar with the building's internal structure. In the event of a fire, visibility becomes the decisive factor in determining life and death. PVC cables produce large amounts of thick black smoke, turning an entire passageway into a "black gas chamber" within minutes. Low-smoke halogen-free cables, on the other hand, offer precious 3 to 10 minutes of evacuation time—often a difference between life and death.

2. Dedicated wiring for escape routes and fire protection facilities.

 Typical locations include evacuation stairwells, fire elevator power lines, emergency lighting systems, fire alarm bus lines, and fire pump control lines. These lines are essentially the "last lines still functioning during a fire." If they burn and release toxic smoke first, they effectively cut off the only lifeline. Therefore, fire codes in many countries worldwide explicitly stipulate that all cables installed inside escape routes must meet low-smoke halogen-free standards.

3. All enclosed spaces with limited ventilation.

Typical locations include underground tunnels, underground utility tunnels, mines, subway platforms and track areas, and ship cabins. In enclosed spaces, air circulation is extremely poor, smoke cannot disperse quickly, and its concentration can rise to lethal levels in a very short time. Even more dangerously, the hydrogen chloride gas produced by PVC combustion, even at low concentrations, can severely irritate the eyes and respiratory tract, rapidly impairing mobility and judgment. Low-smoke halogen-free cables are practically the only universally permitted cable type in these environments.

4. Locations Extremely Sensitive to Corrosion of Metals and Electronic Equipment
Typical locations include data centers, control rooms, communication base stations, bank transaction system server rooms, and hospital operating rooms and ICU equipment areas. In these scenarios, the most critical protection target is not people, but equipment. The acidic gases produced by burning PVC cables can corrode circuit boards, connectors, and relay contacts in a very short time, leading to short circuits or permanent failure. Often, the fire itself may not be large, but after extinguishing, the entire server room may be rendered unusable due to corrosion, resulting in losses several times or even dozens of times greater than the direct fire damage. Low-smoke halogen-free cables can maximize the protection of these high-value electronic devices, significantly reducing secondary losses.

5. Buildings Explicitly Required by Law or Project Specifications
Typical locations include high-rise buildings exceeding a certain height (e.g., 18 or 24 meters or more), large underground parking garages, and facilities for the elderly and children. The reason here is the simplest and most direct—the law does not allow you to use other types of cables. In the UK, for example, Appendix B of the Building Code has clear requirements for cables in the common areas of high-rise residential buildings; in China, the "Standard for Electrical Design of Civil Buildings" GB 51348 also stipulates that halogen-free, low-smoke, flame-retardant cables must be used in various locations. Ignoring these mandatory requirements in overseas project bidding will directly lead to acceptance failure and clear legal liabilities.

6. Voluntary Standards for Enterprises Pursuing International Safety Production Certification
Typical scenarios include projects aiming for LEED (Leadership in Energy and Environmental Design) certification, BREEAM certification, or ISO 14001 environmental management system certification. Even in areas where local laws do not yet mandate it, many multinational corporations, large insurance companies, and high-standard property management companies have already adopted "using low-smoke, halogen-free cables throughout" as an internal safety standard. This practice not only helps reduce insurance costs and improve building ratings but also significantly reduces the risk of business interruption due to fire, often making it a more economical choice from a life-cycle perspective.

III. Limitations of Low-Smoke, Halogen-Free Cables
It must be objectively pointed out that low-smoke, halogen-free cables are not the best choice in all scenarios. First, low-smoke halogen-free materials have slightly lower flexibility. Their tensile strength and bending radius are generally inferior to PVC or rubber-sheathed cables of the same specifications. In scenarios requiring frequent bending or dragging, such as power tool cords and crane cable chains, low-smoke halogen-free cables may actually be more prone to damage.

Second, low-smoke halogen-free cables are more expensive. Their raw material costs and manufacturing processes are approximately 20% to 40% higher than PVC. Using low-smoke halogen-free cables in unnecessary projects will significantly increase the budget burden, resources that could be used for more effective safety measures.

Furthermore, low-smoke halogen-free cables have certain requirements for the construction environment. In extremely humid or long-term submerged environments, such as outdoor direct burial or underwater sections of drainage pumping stations, special waterproof low-smoke halogen-free cables must be selected. The long-term water resistance of ordinary low-smoke halogen-free materials is often inferior to certain specialized PVC or polyethylene materials.

Therefore, the correct engineering logic is: use what is necessary where it is needed, and don't waste budget on unnecessary places. A responsible electrical engineer should make reasonable choices based on risk analysis rather than "use the best for everything for safety."

IV. Conclusion: Remember "When to Use" in One Sentence

In the field of fire protection engineering, there is a repeatedly verified truth: most fire fatalities do not die from the flames themselves, but from being robbed of their lives or sense of direction by dense smoke and toxic gases. Low-smoke halogen-free cables cannot prevent fires from starting, but they can prevent a fire from becoming a "death trap with no exit."

So, when exactly should low-smoke halogen-free cables be used? We can make a judgment based on different types of scenarios.

For densely populated public places with difficult evacuation routes, all escape routes and dedicated fire protection lines, and any enclosed spaces with limited ventilation, low-smoke halogen-free cables are essential; there are no alternatives. In these scenarios, personnel safety directly depends on a low-smoke and non-toxic gas environment.

For locations where equipment is expensive and acid corrosion is unacceptable, such as data centers, control rooms, communication base stations, and hospital operating rooms, the use of low-smoke halogen-free cables is strongly recommended. While both equipment and personnel need protection, the primary consideration here is to avoid irreparable corrosion damage to high-value electronic equipment caused by acidic gases.

For building types explicitly required by law or project specifications, such as high-rise buildings, large underground parking garages, and facilities for the elderly or children, the regulations must be followed unconditionally, with no room for negotiation.

However, for outdoor direct burial environments, situations requiring frequent bending and movement, or general projects with extremely limited budgets and no significant personnel safety risks, alternatives to low-smoke halogen-free cables can be considered. In these scenarios, choosing other cable types does not introduce unacceptable safety risks; in fact, it may be more reasonable in terms of cost and lifespan.

For any responsible electrical designer, engineering contractor, or facility manager, the reason for choosing low-smoke halogen-free cables is never because they are "more expensive" or "more advanced," but because in those critical scenarios—you have no other choice.