In recent years, there has been an increased focus on the use of halogen-free cables in electrical installations. Halogen-free cables are cables that do not contain any halogenated flame retardants. These flame retardants are often used in traditional cables, but they can be released into the air when the cable is burned, posing a serious health hazard.
Every day significant investments are made in the construction of commercial buildings, hotels, hospitals, restaurants, subways, and nightclubs, among others. When we disembark at an airport, when we stay in a hotel, eat dinner in a restaurant, take a subway or even go to see our team play in a football stadium, we often do not even realize what is there. Behind these wonderful constructions, how their materials were specified, and how the entrepreneur took care of the safety of people and property in emergencies.
In principle, if we are well served in a store in a shopping center, we will gladly return to it for a new purchase. The store is well organized, the vendors are attentive, and the products are of good quality. But has it ever occurred to you to ask the sellers if the tens of kilometers of electrical cables installed in the store will not affect people in the event of a fire? Of course not, and nobody wants to worry about this. The one who should be concerned is the designer of the place, who even has criminal responsibility for the electrical design of that store. For it is very important that you correctly specify all the materials, always thinking about the safety of people in a situation that we do not want to happen, but that represents a risk to life and the need to preserve heritage.
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Unfortunately, fires happen frequently, everywhere, and in all types of facilities. The damage is often only material, but there is always a risk of serious injury and death. Burning materials can emit toxic gases, corrosive gases, and black smoke and can also serve to fuel and spread the fire. Often, the fatal victims of the fire were not affected by the fire, but by the gases of the materials burned on the site, mainly due to their speed of spread. When inhaled by humans, they cause asphyxiation.
We all remember some tragic events where many people lost their lives in places of high population density. And what do these events have in common? The concentration of many people in places where evacuation is slow in an emergency.
Regardless of the causes of fires, something must be done to prevent or minimize the effect produced by fire, in order to provide more safety for people. If a fire starts, they should see light signals pointing to emergency exits without being obscured by smoke, they should continue to breathe fresh air or, at most, non-toxic products of combustion. The materials must not be the bridge that transmits the fire from one floor to another.
Such large-scale fires cause widespread commotion and put pressure on authorities to review their fire control codes and protocols. One of the forms of control, which must be exercised by local authorities, is to demand that each one of the product segments of the materials used in the construction and furnishings of the establishments be studied and improved so as not to contribute to worsening the situation in the event of fire Engineering is capable of developing materials with better fire performance, to minimize unwanted results caused by the materials themselves.
Limitations
In this sense, the national technical standards, such as the Paraguayan Standard NP 2 028 13 – Low Voltage Electrical Installations, classify places from the point of view of evacuating people in emergency situations. Halogenated cables (that is, cables containing PVC in their composition) are prohibited in the following situations, in accordance with point 5.2.2 of the said standard:
BD2: low occupancy density, long escape route (residential buildings over 50 m in height and non-residential buildings with low occupancy density and height over 28 m).
BD3: high occupancy density, short escape route (places of the influx of audiences such as theaters, cinemas, department stores, schools, etc. Non-residential buildings with high occupancy density and height less than 28 m).
BD4: high occupancy density, long escape route (places of greater public affluence, such as shopping malls, large hotels, and hospitals, educational establishments that occupy several floors of a building, etc.; non-residential buildings with high occupancy density and height over 28m).
WHERE TO USE THE HALOGEN-FREE CABLES?
Halogen-free cables can be used in any type of installation, even in our homes, why not? But always thinking about the safety of people and property, they must be used in all places where there is a large influx of people.
But how many people must be in the place for it to be considered a place with a high influx of people? Fifty? 100? 1,000? A movie theater for 30 people is a place of great concentration of people.
To help us in this answer and even to standardize this choice, which is somewhat subjective, we can use the Brazilian standard NBR 13570 – Electrical installations in places of public affluence – Specific requirements. This standard establishes the specific requirements necessary for electrical installations in places of public influx, in order to guarantee their correct operation, the safety of people and domestic animals, and the conservation of the property.
ELECTRIC CABLES
The most common cables used in civil construction are insulated in PVC (polyvinyl chloride) and can also be covered in PVC, which provides mechanical protection. Multicore cables also use PVC as the inner layer to make them round. The “C” in PVC translates to the element “chlorine,” from the halogen family of the periodic table. It is not an element that we should fear in its natural form, because every day we drink water with a little chlorine that helps purify it. However, it becomes the villain in case of fire, since it reacts with hydrogen in the air during its combustion, giving rise to hydrochloric acid, a toxic and corrosive gas, deadly to humans and harmful to electrical installations. It is also undesirable to release dark smoke during combustion,
For this reason, we cannot use PVC in facilities with a large number of people. The alternative is to look for halogen-free materials that meet all the electrical and mechanical requirements originally required for electrical cables, in addition to the new chemical requirements, and with excellent fire performance. Good polymer suppliers have developed excellent materials to fill the gap left by PVC.
The standards were developed or changed to include the necessary technical characteristics to guarantee the new requirements: called LSHF (Low Smoke Zero Halogen) or LSOH (Low Smoke Zero Halogen), the cables must be flame retardant, halogen-free, and with low smoke and toxic gas emissions. The standards assigned new designations for the compounds, replacing, for example, the outer layer designated as ST2 (where PVC was applied) by ST8 (IEC 60502-1 standard) or SHF1 (non-halogenated thermoplastic material according to the Brazilian standard NBR 13248). ) . The conductors and the type of braiding are the same, and they continue to be insulated with XLPE or HEPR as long as they are halogen-free.
TESTS AND PERFORMANCE IN THE EVENT OF FIRE
To test the performance of products in a fire situation, various test methods have been developed to classify materials and verify the behavior of the entire cable when burned.
The main requirements are:
- Use of compounds with a high oxygen index (which translates into a quantity of oxygen much greater than that existing in the air to initiate combustion, delaying the combustion process);
- Reduced opacity: low smoke emission, with transmittance greater than 60% or 70% to allow visibility in the search for the escape route;
- Qualitative gas analysis of chlorine, fluorine, bromine, iodine, sulfur, and nitrogen;
- Acid gas amount, the maximum specified value of 5 mg/g acid gas content;
- Determination of the toxicity index, tested for the content of toxic gases in the smoke, after combustion, and must present toxicity indexes equal to or less than 5.
Other codes and regulations must be considered and reviewed, such as the Fire Department Technical Instructions, for example. In cities like São Paulo, firefighters have been considering, for more than ten years, the inspection of the type of cable that is installed in places with a large number of people. If the project was built with PVC-containing cables in its construction instead of halogen-free cables, the site’s operating license is simply not issued, until its managers comply with safety standards.
The designer of the electrical installation must bear in mind that the use of halogen-free cables is not a luxury or a whim, but rather a technical and even moral obligation since their first concern must be the safety of the company. With the large-scale sale as it is today, halogen-free cables are sold at practically the same price or with very little difference compared to halogenated cables, even with special materials and much better performance in case of contact with the fire. In this sense, it is necessary to highlight some characteristics that differentiate the performance of the cables at the time of the fire that must be taken into account when specifying the cables:
Characteristics
Cable with flame retardant characteristics: in this case, the cable is prevented from being the source of a fire caused by a minor incident, such as an external heat source inadvertently coming into contact with the cable. The test is simple, just send 60 cm of wire to the flame of a Bunsen burner for 1 minute, and the charred part cannot exceed 50 cm after removing the flame. But a cable that is only fireproof is not enough to provide safety for the installation, since in a vertical shaft we can have many cables in contact, taking the fire to other floors of the building.
Cable with flame-free propagation characteristics: To obtain this characteristic, the materials and construction of the cable must be studied because the requirement is much more stringent. Here we have 3 main classifications: categories C, B, and A. The difference between them is the time they withstand the fire and the amount of material to burn in the cable, according to the following classification:
Category C: it is the softest, it requires 3.5 dm³ of linear meter of combustible material that burns for 20 minutes. It is required in environments and facilities where there will be a large influx of people, such as shopping malls, hospitals, hotels, restaurants, airports, etc.
Category B: requires 3.5 dm³ linear meters of combustible material that burns for 40 minutes. Today it is only required by the Metro;
Category A: is the most severe, with 7 dm³ of linear meter of combustible material burning for 40 minutes. It is only required for cables for ships and offshore platforms.
Other Classification
Fire-resistant cable: This feature only applies to special safety circuits where the integrity of power lines is required under fire conditions, such as alarm systems, lighting, or even elevators that may continue to operate for some time in the course of the fire. Cables generally have mica strips around their conductors, delaying the attack of fire as much as possible. The test is carried out with the cable under tension and in a burner for 3 hours.
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