How dangerous are fire bulbs

This topic is quite extensive, so I want to note right away that in this article we will consider the issue of the fire hazard of lamps used exclusively in everyday life.

Lamp holders fire hazard

During operation, the lamp holders of the product can cause a fire from a short circuit inside the cartridge, from overload currents, from a large transient resistance in the contact parts.

From a short circuit, a short circuit between phase and neutral in the lamp holders is possible. In this case, the cause of the fire is electric arcaccompanying short circuits as well as overheating of contact parts due to the thermal effects of short circuit currents.

Overloading of cassettes by current is possible when connecting bulbs with a power that exceeds the nominal one for a given cassette. Usually, ignition during overload is also associated with an increased voltage drop in the contacts.

The increase in contact voltage drop increases with increasing contact resistance and load current.The greater the voltage drop across the contacts, the more they heat up and the more likely it is to ignite the plastic or wires connected to the contacts.

In some cases, it is also possible for the insulation of power wires and cables to catch fire as a result of deterioration of the live conductors and aging of the insulation.

Everything described here also applies to other wiring products (contacts, switches). Especially fire-hazardous are wiring accessories that have poor-quality assembly or certain design flaws, for example, the lack of mechanisms for immediate disconnection of contacts in cheap switches, etc.

But let's get back to considering the fire hazard of light sources.

The main cause of fires from any electric lamps is the ignition of materials and structures by the thermal effects of the lamps in conditions of limited heat dissipation. This can happen due to the installation of the lamp directly on combustible materials and structures, covering the lamps with combustible materials, as well as due to structural defects of the lighting fixtures or incorrect position of the lighting fixture — without removing heat, as required by the technical documentation for the light fixture.

Incandescent light bulb fire hazard

In incandescent lamps, electrical energy is converted into light and heat energy, and heat makes up a large proportion of the total energy, and therefore incandescent lamp bulbs heat up very decently and have significant thermal effects on objects and materials around the lamp.

The heating during the burning of the lamp is unevenly distributed over its surface.So, for a gas-filled lamp with a power of 200 W, the temperature of the wall of the bulb along its height with vertical suspension during measurements was: at the base — 82 ОС, in the middle of the height of the bulb — 165 ОС, at the bottom of the bulb — 85 OS.

Having an air gap between the lamp and any object significantly reduces its heating. If the temperature of the bulb at its end is equal to 80 °C for a 100 W incandescent lamp, then the temperature at a distance of 2 cm from the end of the bulb is already 35 ° C, at a distance of 10 cm — 22 °C, and at a distance of 20 cm — 20 OS.

If the bulb of an incandescent lamp comes into contact with bodies of low thermal conductivity (cloth, paper, wood, etc.), severe overheating is possible in the contact area as a result of deterioration of heat dissipation. So, for example, I have a 100-watt light bulb with an incandescent filament wrapped in a cotton cloth, after 1 minute after switching on in a horizontal position, it warmed up to 79 ° C, after two minutes - to 103 ° C, and after 5 minutes - to 340 ° C , after which it began to smolder (and this can cause a fire).

Temperature measurements are made using a thermocouple.

I will give a few more figures obtained as a result of the measurements. Maybe someone will find them useful.

So the bulb temperature of a 40 W incandescent lamp (one of the most common lamp wattages in household lamps) is 113 degrees 10 minutes after the lamp is turned on, after 30 minutes. — 147 OS.

A 75 W lamp heats up to 250 degrees after 15 minutes. True, in the future the temperature of the lamp bulb stabilized and practically did not change (after 30 minutes it was about the same 250 degrees).

A 25 W incandescent bulb heats up to 100 degrees.

The most serious temperatures are recorded on the bulb in a photo of a 275 W lamp. Within 2 minutes of switching on the temperature reached 485 degrees and after 12 minutes it reached 550 degrees.

When halogen lamps are used (according to the principle of operation, they are close relatives of incandescent lamps), the question of fire danger is also, if not more acute.

It is especially important to take into account the ability to generate heat in large quantities with halogen lamps when it is necessary to use them on wooden surfaces, which, by the way, happens quite often. In this case, it is recommended to use low-voltage halogen lamps (12 V) with low power. So, already with a 20 W halogen bulb, pine structures begin to dry out, and chipboard materials emit formaldehyde. Bulbs with a power of more than 20 W are even hotter, which is fraught with self-ignition.

In this case, special attention should be paid when choosing the design of lighting fixtures for halogen lamps. Modern high-quality light fixtures themselves insulate the materials around the light fixture from heat quite well. The main thing is that the light fixture is free to lose this heat, and the design of the light fixture as a whole is not a thermos for heat.

If we touch on the generally accepted opinion that halogen lamps with special reflectors (for example, so-called dichroic lamps) practically do not emit heat, this is a clear fallacy. A dichroic reflector acts as a mirror for visible light, but blocks most of the infrared (heat) radiation. All the heat is returned back to the lamp.Therefore, dichroic lamps heat up the illuminated object (a cold beam of light) less, but at the same time heat up the lamp itself much more than conventional halogen lamps and incandescent lamps.

Fluorescent lamp fire hazard

As for modern fluorescent lamps (eg T5 and T2) and all fluorescent lamps with electronic ballasts, I do not yet have information on their large thermal effects. Let's look at the possible reasons for the appearance of high temperatures on fluorescent lamps with standard electromagnetic ballasts. Despite the fact that such ballasts are almost completely banned in Europe, they are still very, very common in our country and it will take a long time before they are completely replaced by electronic ballasts.

In terms of the physical process of producing light, fluorescent lamps convert a greater proportion of electricity into visible light radiation than incandescent lamps. However, under certain conditions associated with malfunctions of the control device of fluorescent lamps ("sticking" of the starter, etc.), their strong heating is possible (in some cases, the heating of the lamps is possible up to 190 — 200 degrees, and suffocating — up to 120).

Such temperatures on the lamps are a consequence of the melting of the electrodes. In addition, if the electrodes are moved closer to the glass of the lamp, the heating can be even more significant (the melting temperature of the electrodes, depending on their material, is 1450 — 3300 OS). As for the possible temperature at the choke ( 100 — 120 ОC), then it is also dangerous, since the softening temperature for the casting mixture according to the standards is 105 ° C.

Starters present a certain fire hazard: they contain highly flammable materials (paper capacitor, cardboard gaskets, etc.).

Fire safety regulations require that the maximum overheating of the support surfaces of the lighting fixtures does not exceed 50 degrees.

In general, the topic covered today is very interesting and quite extensive, so in the future we will definitely return to it again.