, Warehouse Fire Hazards – Part 1: High Intensity Discharge Lighting, Harrington Group Inc

There are many fire hazards commonly present in warehouses beyond the obvious presence of high combustible loading from rack and palletized storage arrays. In this blog series, we will review three of those hazards: High Intensity Discharge lighting, idle pallets, and unique hazards associated with cold storage warehouses.

High Intensity Discharge Lighting

According to Wikipedia, High Intensity Discharge (HID) lighting is a type of electrical gas-discharge lamp that produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts. The gas facilitates the arc’s initial strike. Once the arc is started, it heats and evaporates the metal salts forming plasma, which greatly increases the intensity of light produced by the arc and reduces its power consumption.

HID lights are available in three basic types:

  • Metal Halide
  • Mercury Vapor
  • High-Pressure Sodium

Metal halide and mercury vapor lights are often found in warehouses, “big box” retail warehouse stores, and sports facilities, while high-pressure sodium lights are typically used for highway and street lights.

HID lights have a sealed quartz or ceramic arc tube with a tungsten electrode at each end, mounted to a metal frame that is sealed within an outer glass bulb and fitted with a base to form a lamp. They have a long life, and provide good lighting for their coverage area.

Failure Modes

Failure of an HID lamp can occur from improper positioning, breakage, or arc tube failure. Lamps are designed to operate in a specific position relative to the base, and lamps positioned improperly will increase the likelihood of a violent failure. Breakage can occur with direct impact from material handling equipment, from scratches on the surface of the lamp, or from contact with water (thermal shock). Arc tube failure can occur from an aging bulb that is nearing the end of its useful life. When these lamps fail violently, extremely hot glass and other lamp parts may fall onto combustible materials below, igniting them and causing a fire.

Recommendations for Existing Facilities

To reduce the potential for catastrophic failure of these lamps in existing HID lighting installations:

  • Confirm the lamp is oriented properly with respect to the base.
  • Confirm the ballasts are designed to provide the appropriate wattage for the lamp.
  • Utilize Type O lamps which have a containment barrier within the lamp.
  • Install a Type O exclusionary socket so that Type E or Type S lamps cannot be mistakenly installed as replacement lamps.
  • Use only UL listed/FM Approved lamps that meet UL 1598 Luminaires.
  • Replace the lamp if the outer glass bulb has been scratched, cracked or damaged in any way.
  • Protect the lamp from contact with liquid, moisture, dust, dirt, oils, etc.
  • Follow all manufacturer’s warnings and instructions for installation & maintenance.
  • Maintain records showing lamp installation dates and replace lamps at 60-75% of rated life.
  • Follow the manufacturer’s recommendations for lamp cycling, typically for 15 minutes weekly, to allow the lamp to cool, so malfunctions can occur in a passive manner.

Insurance companies have recognized the hazards associated with the presence of HID lighting, and many offer informational bulletins that outline best practices to reduce the potential for fire with the use of HID lighting.

Factory Mutual datasheet 5-21 Metal Halide High Intensity Discharge (HID) Lighting provides guidance and recommendations to reduce the potential for fire originating from the use of HID lighting in a facility. FM Datasheets are available online (free) at https://www.fmglobal.com/fmglobalregistration/.

The National Electrical Manufacturers Association (NEMA) offers a document (LSD 25-2004) that also provides guidance and best practices for the use of Metal Halide Lighting Systems and is available at the following link: http://www.geappliances.com/email/lighting/specifier/2008_07/downloads/NEMABestPractices.pdf

Recommendations for New Facilities

New construction projects will likely incorporate the use of LED lighting instead of HID lighting.  In addition to the much lower fire risk, LED lighting has a lower maintenance cost, lower power consumption, no flicker, is dimmable, has instant ignition of light, has no mercury content, and has a life span approximately five times that of HID lighting.


Lighting technology is moving away from the use of HID lights in facilities, but the popularity of HID lighting in the past, means there are a lot of existing HID lighting installations still in service in facilities throughout the world. Being aware of the fire hazards they pose, and taking proper precautions will help reduce the potential for fires that originate from HID lighting.

Stay tuned for Part 2 of this blog series, which will review fire hazards associated with idle pallets.