Superglue fuming in crime scene investigations

DEFINITION: Use of cyanoacrylate vapors to visualize latent fingerprints.

SIGNIFICANCE: Fingerprints and palm prints are often critical pieces of evidence encountered at crime scenes. Because most fingerprints are not visible to the naked eye and are easily destroyed, the fuming of prints with the vapors of superglue (cyanoacrylate) has become common. This technique makes permanent what would otherwise be transient pieces of evidence.

Forensic scientists have used since 1982 to visualize latent fingerprints and palm prints on nonporous surfaces such as metals and plastics. The developed prints are white and provide especially good contrast with dark-colored surfaces. Dyes such as rhodamine can be used to enhance the contrast of prints with light backgrounds and can cause prints to fluoresce when viewed under the appropriate conditions.

How Fuming Works

Superglue, like many adhesives, is a polymer. A polymer is a type of molecule that exists in the form of long chains of repeating units, called monomers. Superglue consists almost entirely of cyanoacrylate ester, which consists of carbon, hydrogen, oxygen, and nitrogen and polymerizes (forms long chains) rapidly in the presence of minute amounts of water.

When superglue vapor comes in contact with a fingerprint on a nonporous surface, it quickly begins polymerizing. Layers of polymer build up until the minute details of the fingerprint are visible. Because the vapor interacts only with the fingerprint, the area around the details remains free of superglue. In addition to enabling visualization of the fingerprint, the superglue makes the print permanent, thus preserving it.

Procedure

Superglue fuming is often performed in a fuming tank. The item to be fumed is suspended or propped inside a glass tank, such as an aquarium, so that the area of the item suspected to contain a fingerprint or palm print is not touching any surface of the tank. A source of superglue vapor is also required. The superglue may be vaporized in one of two ways: Either a small amount of sodium hydroxide, a very strong base, is added to the unpolymerized glue or the glue is heated. Crime labs typically employ the heating method, as it tends to be more efficient, but methods of heating the glue vary from lab to lab. The heat source can be anything from a lightbulb to a small warming plate (of the kind designed to hold a coffee mug) to a cup of boiling water.

To begin the fuming, a small amount of superglue (roughly the size of a quarter) is typically placed on an aluminum foil tray, which is then placed above the heat source inside the fuming tank, along with the item to be fumed. The tank is then sealed, and the vapor is allowed to fill the chamber. The vapor interacts with the object in the tank and develops any prints that might be present on the surface. The fuming is allowed to progress for anywhere from less than an hour to six hours, depending on the efficiency of the heat source, the lab’s protocols, the size of the tank, and the object being fumed. When the fuming is complete, the heat source is turned off and the tank is opened. The fumed object can then be removed and examined for developed prints.

Another fuming technique involves the use of a handheld fuming wand, which contains solid superglue along with a butane torch. The torch heats the superglue and causes it to vaporize quickly. These fumes can be directed onto the surface of interest, and high-quality prints can be developed in minutes. An advantage to this method is that most handheld fuming wands are portable, so they can be taken to crime scenes and used to fume large objects that cannot be transported to the lab. Such wands can also be used as vapor sources in traditional fuming tank setups.

Safety Considerations

Although superglue is nontoxic—it is even sometimes used to seal surgical wounds—the vapors given off during the fuming process will bind to skin, eyes, and mucous membranes if these are left unprotected. Persons wearing contact lenses should not come into close proximity to superglue fuming because of the possibility that the lenses will bond to the eyes. The fumes themselves can also be very irritating. To prevent exposure, laboratories generally conduct superglue fuming in chemical fume hoods, and those performing the procedure wear safety goggles and gloves and make sure that none of their skin is exposed.

If a fume hood is not available, such as when a fuming wand is used at a crime scene, extra care must be taken to ensure that no one is exposed to the fumes. In addition to wearing the kinds of personal protective gear noted above, the person using a fuming wand often employs a face mask to avoid inhaling the vapors.

Bibliography

Champod, Christophe. Fingerprints and Other Ridge Skin Impressions. Boca Raton, Fla.: CRC Press, 2004.

Gardner, Ross M. Practical Crime Scene Processing and Investigation. Boca Raton, Fla.: CRC Press, 2005.

Genge, N. E. The Forensic Casebook: The Science of Crime Scene Investigation. New York: Ballantine, 2002.

"Evidence Response Training: Cyanoacrylate Fuming." Federal Bureau of Investigation, 2024, www.fbi.gov/video-repository/ert-training-fuming-072021.mp4/view. Accessed 19 Aug. 2024.

Jackson, Andrew R. W., and Julie M. Jackson. Forensic Science. 2d ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2008.

Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 13th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2020.