Most fire deaths are due to asphyxiation caused by smoke inhalation
Existing smoke detectors only measure smoke concentration, so accuracy is low.
Must be able to identify the cause of fire according to UL 217 8th standard


In Korea, fire alarms are equipment that must be installed in most buildings according to the Building Act. However, fire alarms that save lives in the event of a fire are usually stigmatized as an eyesore. The National Fire Agency announced that in 2019, the number of dispatches due to malfunctioning fire alarms was 7.6% of the total number of fire-related dispatches (8,130 cases) over the past five years.

There are countless buildings where the fire alarms are turned off. The situation is similar not only in Korea but also overseas. According to a report by the National Fire Protection Association (NFPA), 23% of fire deaths in the United States occurred in buildings where fire alarms were intentionally disabled, even though they were installed.

The development of fire alarms capable of accurate alarms is urgent. As the saying goes, “If there is no smoke, there will be smoke in the chimney,” smoke is the most reliable sign of fire. The majority of fire deaths are due to asphyxiation caused by smoke inhalation. Therefore, accurately and quickly detecting smoke leads to increased fire alarm accuracy and prevention of fire accidents.

In 2018, UL, an American safety standards development and certification organization, announced the smoke alarm standard, UL 217 8th. Manufacturers of fire alarms and smoke detectors are faced with the challenge of manufacturing products that comply with UL 217 8th standard while also providing increased accuracy and reliability.

To support these manufacturers, Analog Devices (ADI) launched the ADPD188BI optical sensor, which integrates two LEDs, a photodiode, and an analog front-end (AFE) into a single package, in line with the specification announcement in June 2018.

We asked Seungkyu Lee, manager in charge of smoke detector products at Analog World, about the principles and limitations of existing smoke detectors and the advantages of the ADPD188BI sensor.



Q. What are the main causes of smoke detector malfunctions?

A. Most smoke detectors used in Korea use one infrared (IR) LED and one photodiode. This method has limitations in distinguishing the cause of fire. In particular, Korea has high concentrations of fine dust and high humidity, making it difficult to distinguish smoke.



Q. Why are there limitations to smoke detection using infrared LEDs and photodiodes?

A. Conventional smoke detectors emit infrared light from an infrared LED, and a photodiode detects the signal that is scattered when it collides with smoke. This determines the presence and concentration of smoke, but it is limited to simple concentration determination, making it impossible to distinguish between various causes of fire.



Q. What is the UL 217 8th standard?

A. Due to recent environmental changes and the acceleration of urbanization, fire alarm standards are becoming more stringent. The UL 217 8th standard is a standard used in the United States, and its basic content is to distinguish the cause of fire. The most basic ones are paper, wood, polyurethane, etc., and in particular, steam and smoke generated when cooking food have been added.



Q. How did the ADI ADPD188BI sensor supporting the UL 217 8th standard overcome the shortcomings of existing smoke detectors?

A. The ADPD188BI sensor uses an infrared LED, a blue LED, and two photodiodes to overcome the shortcomings of other smoke detectors. First, it uses two LEDs with different wavelengths to obtain the signal size. This is changed to the concept of Proton Transfer Reaction (PTR), and the ratio is analyzed to distinguish the cause of the fire.



Q. How does backscatter design reduce smoke detector PCB size?

A. The ADPD188BI sensor, the first in the industry to be offered in a modular format, has a wall built around the photodiode to prevent the LED light from being directly received, and is designed so that the LED light that collides with smoke is scattered backwards. The ADPD188BI sensor alone can capture pure smoke data, reducing the need for other devices, and its small footprint makes it suitable for designing smaller smoke detectors than existing ones.



Q. What is the role of the chamber provided with the ADPD188BI sensor?

A. The chamber basically reduces the surrounding signal noise and also acts as a dark room. It is also designed so that the LED light that hits the chamber wall is not received by the photodiode.



Q. What support does Analog World provide for ADPD188BI sensor users?

A. Analog World provides a demo board (EVAL-ADPD188BI) and the algorithms required to distinguish smoke, dust, and water vapor in domestic environments.