Audible smoke alarms remain the most effective alarm to wake a sleeping person with mild to moderately severe hearing loss, but may not be effective with young adults who are impaired by alcohol. These findings are the result of two separate research studies from the National Fire Protection Association's Fire Protection Research Foundation.

Waking Effectiveness of Alarms for Adults Who are Hard of Hearing looked at several auditory signals and a variety of alternative alarms that employ methods other than sound, such as bed shakers, pillow shakers and strobe lights for their effectiveness in alerting hard-of-hearing individuals of an emergency when they were asleep.

Results showed that the standard audible emergency evacuation signal (a repeating pattern of three tones and a pause) with a lower-pitch tone (520HZ square wave) awakened 92% of the hard-of-hearing participants when used at or below the code-minimum sound level of 75dB for 30 seconds.

The same device awakened all of the participants when raised to 95dB, the typical sound level produced by smoke alarms. It also was noted that participants who awoke to signals were most likely do so within the first 10 seconds of the signal being on. The lower-pitch tone was found to be significantly more effective than the higher-pitch tone (typically 3,150HZ) commonly used in smoke alarms and other alerting appliances.

“It makes sense that people at higher risk of not waking up to a smoke alarm, like those hard of hearing, might seek alternative devices that they feel are more likely to alert them in an emergency situation,” said Kathleen Almand, executive director of the Fire Protection Research Foundation. “Finding that an auditory signal at a low pitch is best for alerting even those mild to moderately hard of hearing will certainly prompt further investigation in this area and ultimately lead to better protection for this high-risk group.”

Bed-shaker and pillow-shaker devices presented alone were successful in awaking 80% to 83% of the hard of hearing participants at the intensity level as purchased. Strobe lights alone were not effective in waking this population with only 27% of participants waking to a strobe light intensity above the lowest level permitted by code for sleeping areas.

The second study, Waking Effectiveness of Alarms for the Alcohol Impaired, examined how alcohol consumption influenced the waking effectiveness of several auditory and alternative signaling devices on a group of 32 adults aged 18 to 26. The study found that the effectiveness of most sounding alarms decreased when individuals were alcohol impaired and asleep; alternative non-sounding methods also were found not to be effective for waking this group.

“Many people that are under the influence of alcohol die in fires,” said Almand. “It is important to understand what works best when alerting someone to an emergency when they are impaired by alcohol and asleep.”

Some auditory signals were found to be an effective means of waking moderately alcohol impaired young adults from deep sleep. The study found that two lower-frequency alarm sounds (400- and 520hz) were significantly more effective than the higher-frequency alarm sound (typically 3,150HZ). Using the minimum sound level permitted by code for sleeping areas, these lower-frequency alarm sounds proved sufficient to wake participants, most within the first 10 seconds.

Alternative methods not effective in waking individuals were bed-shaker and pillow-shaker devices, which only awoke 58% to 65% of the group, used at the intensity level of the device as purchased. Strobe lights also were not effective, with only 24% waking at the lowest strobe light intensity.