High intensity discharge (HID) lamps (mercury vapor, metal halide, and high pressure sodium) can bring the brightness of the sun into gymnasiums, pools, and other large indoor spaces. Their use can reduce replacement and maintenance costs because of their longevity but they do have disadvantages – some of which are merely inconvenient while others are more significant.
Gymnasium light bulbs are frequently broken – struck by an errant volley ball return, a miss-kicked soccer ball, or a ball that kids meant to get stuck in the roof trusses. No matter what type of lamp is used, the result can be glass showering down on players or spectators unless a fully enclosed protective case protects the lamp and contains broken pieces in case of failure. If the lamp is HID, that falling glass is nearly 2,000o F and mercury may be part of the debris raining on everything below.
A bigger danger, however, is when a HID light is only partially broken – i.e., damaged but still producing light. A second layer of glass normally protects us from the massive levels of ultra-violet (UV) light produced by these bulbs. If that outer layer is cracked or broken, the protective barrier is compromised and anyone in the immediate area can be seriously burned. There have been multiple cases in the last few years, each involving 80 to 100 people. The US Food & Drug Administration has issued multiple warnings, as have several states.
Complicating the issue is that all HID lamps are not created equal. The basic lamps are Type R and they are the lamps that were involved in the noted incidents.
Although their outer bulb is damaged or broken, the bulb can continue to function, radiating unshielded UV-light on everything in the area. A second type of lamp is called Type T. These globes have a self extinguishing feature that is designed to shut down the light within 15 minutes if the outer shell is broken. The current National Electric Code advises a full enclosure with a heavy glass or plastic shield for Type R lamps to reduce the potential for breakage and thus lessen the potential of damaged bulbs releasing unshielded UV-light.
Threats come from many different sources. Gym lights are generally taken for granted, especially when they are operating. Don’t expose those who use your facilities to possible UV-burns or mercury exposure. Use Type T bulbs in an appropriate fixture that both protects the bulb from damage and keeps any broken debris from falling onto those below. Your local lighting supplier can identify your current bulbs and suggest suitable replacements.