Story highlights Prepackaged coffee filters can build up pressure on airplanes

If the filters are not inserted properly, water can become blocked

Crews and passengers have suffered burns when incorrectly used filters exploded

When a flight attendant serves up a cup of coffee, fliers are unlikely aware of just how much risk the crew took to deliver them that cup of joe.

According to a safety alert published on the Federal Aviation Administration's website, the prepackaged coffee filters many airlines use are susceptible to pressure buildup and can explode when an unsuspecting attendant lifts the coffee pot to pour a cup.

Coffee makers on airplanes, similar to home drip-style coffee makers, have the filter and coffee grounds above the coffee pot. Many airlines use prepackaged coffee sealed within the coffee filter for convenience and ease of cleanup.

When the filters are incorrectly placed in the coffee maker the water can become blocked from dripping into the coffee pot below and pressure builds up within the container holding the filter and coffee grounds. When an unsuspecting flight attendant removes the coffee pot, the clogged compartment above suddenly has much more room to expand and the filter can burst, with its hot contents and hot water possibly injuring passengers and crew.

Several cases of bursting java filters have caused flight crew and passengers to suffer first- and second-degree burns, according to the FAA's warning.

"The coffee filter containing the hot coffee grounds can burst causing burns to the face, neck, hands, arms and torso in varying degrees of severity," the FAA's safety alert said. The alert was issued to airlines and aircraft operators on January 3.

A good indication that a coffee filter container is about to explode is water overflow and a hissing noise coming from the coffee maker, the FAA said. When it looks like the coffee filter package is about to blow, passengers and crew nearby should get out of the way and not touch the coffee pot. Power to the coffee maker should be disconnected, the FAA said.

To further prevent accidents, the agency is warning flight crews to make sure the filter packages aren't folded and that they are installed correctly before starting the brew.

The FAA is encouraging air carriers and operators to add their warnings to flight-attendant manuals, training manuals and by warning crew members of the dangers of making coffee incorrectly.