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What Are the Dangers of Exposed Incandescent Bulbs?

Chris Deziel

The original light bulbs were incandescents, but legislation enacted in Canada and the United States in 2012 has greatly reduced their use in favor of more energy-efficient alternatives.

In a small, unventilated space, an incandescent bulb is a fire hazard.

Incandescents weren’t banned for safety reasons -- CFL and halogen bulbs are more hazardous -- but they aren’t 100 percent safe either. They are made with thin glass that shatters easily, and If you leave one exposed, it can start a fire.

A Glowing Filament

An incandescent bulb produces light when electricity passes through its tungsten filament and causes the filament to glow. The electrical resistance that produces the light also produces heat, which accounts for as much of 95 percent of the energy output. When it’s glowing, the temperature of the filament is around 2,200 degrees Celsius (4,000 degrees Fahrenheit), and this heats the gases in the bulb, which in turn heat the glass enclosure to as much as 260 degrees Celsius (500 degrees Fahrenheit).

Fire Danger

Circulating air often cools the surfaces of exposed incandescent bulbs, but the temperature quickly rises when a bulb is used in a small, unventilated space, such as a closet or storage room. It can ignite flammable items placed too close to it, such as cardboard boxes or items of clothing. Exposed bulbs can even ignite the pull strings attached to porcelain fixtures, which can fall onto other flammable materials and start a fire. Even non-flammable pull-chains are dangerous; when in contact with an exposed bulb, they can conduct heat into the fixture, overheat the electrical wires and start a fire.

Thin Glass Shell

Unlike CFL bulbs, incandescent ones don’t contain mercury, and breaking one doesn’t expose you to toxic fumes. Instead, incandescent bulbs usually contain an inert gas, such as argon, to prevent the filament from corroding, and the gas is contained in a thin glass shell. The shell is fragile, and if it breaks, it produces thin shards of glass that easily penetrate skin and eye tissues and can even be inhaled. Incandescent bulbs pose a hazard when carelessly thrown in the trash, creating shards that can cut unsuspecting waste facility workers. They should be recycled according to local ordinances.

Removing an Old Bulb

The base of a bulb that has been in use for several years often corrodes, especially if the fixture is in a humid location. This creates a hazard when it’s time to replace the bulb, because you can break the glass when trying to unscrew it. Not only does the glass cut your hands, but the base remains in the fixture and can potentially shock anyone who touches it while the power is on. Always wait for a burned-out bulb to cool, then turn off the power and put on protective gloves before unscrewing it.