Fire Technology

, Volume 50, Issue 3, pp 791–803

Development of a Sensing Device to Reduce the Risk from Kitchen Fires

Article

DOI: 10.1007/s10694-012-0278-5

Cite this article as:
Lushaka, B. & Zalok, E. Fire Technol (2014) 50: 791. doi:10.1007/s10694-012-0278-5

Abstract

Fires originating from cooking areas are the second leading cause of fatalities and loss related to residential fires. The predominant root cause of residential stovetop cooking fires has been found to result from unattended cooking. The installation of smoke detectors can only detect and at best alert residents to a fire hazard. Control technologies for cutting gas supply to cooking devices upon receiving signals from detectors is not new. Many of stovetop mitigation technologies are currently in existence as consumer products or patents, however little evaluation has been conducted on these products in order to develop a more efficient and effective device to help reduce the frequency of cooking related fires. The paper presents a short review of literature and goes on to discuss a fire sensing device developed to act as a pre-ignition sensor that will cut off power supply to cooking devices upon receiving inputs from a detection device. The device proved to be effective when it was tested both in the laboratory and a real kitchen environment. The installation of this device, in addition to an installed detection device will play a major role in reducing the risk of most kitchen fires.

Keywords

Fire sensing device Kitchen fire Smoke detector Pre-ignition Risk of fire 

1 Introduction

Fires have always been a threat to public safety in terms of potential death, injury, and financial costs. In 2002, Canada recorded a total of 53,589 reported fire cases. According to the Council of Canadian Fire Marshals (2002), this accounted for $1,489,012,263 in property losses, with residential properties accounting for majority of this incidence (41%). The residential fire incident data collected over the 8 year period (1995–2003) from British Columbia, Alberta and Ontario shows 97,267 fires and 1,327 deaths. A significant portion of residential fires stem from a cooking equipment, most often a range or stovetop. Existing fire data indicate that these fires primarily are unattended [1]. For example, in 25.8% cases, cooking areas or kitchen was found to be the leading cause of residential fires. In contrast, living and the sleeping areas were found to be a cause in only 11.5% and 10% cases respectively [2, 3]. A more specific data for Ontario between 1995 and 2003, recorded 6,739 fires with 717 reported deaths. Most of these reported fire cases (28.6%) occurred in cooking areas, similar to the overall data presented above [4]. Furthermore, fires originating from the kitchen also resulted in most injuries with a recorded value of 30.3% of all residential fire related injuries. Other spaces such as the sleeping and living areas recorded only 19.0% and 17.2% of injuries respectively. In terms of total estimated loss (in CAD dollars) 39.7% was related with kitchen, living and sleeping areas. Out of this value, 12.6% of estimated loss was a result of kitchen fires.

The issue of cooking related fires is a major problem that needs urgent attention. For example, stovetop cooking fires continue to be a leading ignition source associated with preventable residential fires, injuries and deaths in Ontario. Analysis of the ‘Ontario Stove Top Survey’ conducted from 2005–2006 reveals that the predominant root cause of residential stovetop cooking fires results from unattended cooking due to homeowner distractions such as answering phone, unexpected visitors, attending to child, falling asleep and forgetfulness. The survey reported that cooking related fires constitute 27% of all fires that are initiated from the kitchen with 69% of fires due to unattended cooking. The survey also reported 205 injuries with an estimated loss of $10.2 million (CAD) [5]. Based on survey results, the Ontario Office of the Fire Marshal [5] recommends the development of effective strategies which must critically consider the unattended cooking scenario for mitigating such fires and thus loss of property and life.

In general, 1990s showed increase in reported deaths, injuries and property loss due to residential fires. Therefore, the consumer product safety commissioner (CPSC) started investigating cooking related fires specifically associated with electric and gas ranges. Over the next several years various cooking fire projects were started by CPSC, with some of the work conducted by the National Institute of Standards and Technology (NIST). The work was divided into two phases, Phase-I and Phase-II, conducted primarily by NIST. In the Phase-I of the work, a total of 22 experiments were conducted using electric (both open coil and smooth top) and gas ranges. All the 22 experiments were consisted of ignition tests with the following food groups: soybean oil, bacon and table sugar. Cooking gears were also studied including differences between pot and pan materials. All the tests indicated that temperature, smoke particulates and hydrocarbon gases were the best parameters for determining pre-ignition. Phase-I of NIST’s work also included search on existing and potential devices, as well as systems or methods capable of detecting the previously determined pre-ignition conditions. Thermocouples were considered as the most promising technology for determining pre-ignition temperatures. In addition, the review suggested that scattering or attenuation types of photoelectric devices are best for detecting smoke particles. Tin oxide and narrow-band infrared absorption sensors were found to be the best form of technology for detecting hydrocarbon gases.

Phase-II, also performed by NIST, was a study to determine if it was possible to differentiate between pre-ignition conditions and regular cooking conditions. Individual and combined pre-ignition indicators were used to determine if there was a difference between the lower limit of hazardous pre-ignition conditions and the upper limit of normal cooking conditions. Forty-three tests covering a total of 21 scenarios were conducted using four different ranges. For the tests NIST used a mix of attended cooking time-period and unattended cooking time-period. It was determined that all individual ignition indicators could detect a stronger signal when approaching pre-ignition conditions. NIST concluded that more research is required in determining the best combination of devices needed for a proficient system. The most promising system included one cooking-alcohol sensor at the front center of the range hood and a thermocouple contacting the bottom of the cooking pan. It was observed that standard house photoelectric and ionization smoke detectors identify pre-ignition condition very well (95% and 81%, respectively), however they generate a large number of false alarms. Ultimately, NIST concluded that pre-fire detection systems for range-top cooking are possible and should be further investigated.

In most homes, detection devices are installed to be able to detect the onset of fire; however these detectors are not designed to prevent fire occurrence. The use of smoke detectors in preventing death is simply to notify residents of the presence of smoke and fire potentially providing them sufficient time to exit [6].

Numerous stovetop mitigation technologies are currently in existence as consumer products or patents. Control technology for shutting down gas and electric cooking units upon receiving signals from an installed detection device is nothing new. This is because gas burners in some appliances have an in-built flame sensor that causes the gas valve to close upon the onset of ignition. For example, some electric stoves have thermostat-controlled override technology that discontinues current to the heating element when the ceramic top temperature approaches levels that could damage the material. Therefore, there is a need to develop a better screening criterion that relates to the following critical issues: maintenance and serviceability of these in-built systems, ease of system operation verification, its operation over the product (stove) life without failure and finally its effectiveness. However, limited or lack of any evaluation on the products (stove) that utilize the above-mentioned technologies is an issue and needs to be taken into consideration. Despite this issue, most of these concerns are either very difficult or costly and time consuming to address based on the product’s (stove) life span by the user. Since the technology is mostly in-built, the only period when the user has the opportunity to verify the effectiveness of these in-built systems is during a fire event by which time it will be too late to prevent any eventualities. A simple but effective device or technology that is able to easily address the concerns raised will go a long way to help reduce the alarming rates of most preventable domestic fires originating from the kitchen.

For the purpose of this paper, a device was designed using an existing smoke detector by adding an external device that will shut off the stove upon detection of approaching ignition by the smoke detector. To come up with this device, a photoelectric detector (one of two types of smoke detectors) was used because of its advantages of being suitable for kitchen environments. For example, the photoelectric smoke detectors are quick in detecting smoldering fires and are less sensitive to false alarms from steam or cooking fumes generated from the kitchen. The paper provides a detailed description of how the device was designed, including the tools used to build the control circuit of this device.

2 Smoke Detectors

Smoke alarms work by sensing smoke and sounding an alarm to notify residents [7]. These detectors consist of two basic parts: a sensor to sense the smoke and a very loud piezoelectric to alert residents. They operate using a 9-V battery or a 120-V house current. There are two most common types of smoke detectors used today: photoelectric detectors and ionization detectors. These detectors are distinguished in the sub-section below:

2.1 Photoelectric Detector

A photoelectric (also called optical) smoke detector is a light sensor. It contains a light source (infrared), a lens to collect the light into a beam and a photoelectric sensor at an angle to the beam as a light detector. Figure 1 shows how photoelectric smoke detector works, “A” is a light source; “B” is photoelectric sensor and red stripes are beams of light.
Figure 1

Light source and sensor

In the absence of the smoke, light enters the detector from ‘A’ and shoots directly across with no interruptions. On the other hand, when smoke enters the chamber as illustrated in Figure 2, the smoke particles reflect and spread the light all over the chamber and some amount of light hits the photoelectric sensor at position B. Once the sensor at position B receives light that has been reflected by the smoke particles within the device, it then sets off the alarm in the smoke detector. Figure 3 shows a typical section through a photoelectric smoke detector with major parts labeled.
Figure 2

Light reflection

Figure 3

Photoelectric smoke detector

The photoelectric smoke detectors are quick in detecting smoky fires. They are less sensitive to false alarms from steam or cooking fumes generated from kitchen or bathroom compared to the ionization smoke detector [8].

2.2 Ionization Detector

This is the second type of smoke detector. The only difference between photoelectric and ionization smoke detector is the technique used to detect smoke. Ionization smoke detectors use an ionization chamber and a source of ionizing radiation to detect smoke. This type of smoke detector is more common because it is less expensive and better at detecting the smaller amounts of smoke produced by flaming fires. These detectors are sensitive and tend to have more false alarms compared to photoelectric detector.

Inside the ionization detector is a small amount of Americium-241. Americium-241 is a radioactive element that has a good source of alpha particles [8]. Figure 4 shows the inside of an ionization smoke detector. The white circular cone located at the top left corner is the piezoelectric, which sounds the alarm.
Figure 4

Ionization smoke detector

The ionization chamber is located to the right of the piezoelectric, Figure 4. The ionization chamber consists of two plates (electrodes) with a voltage across them, along with a radioactive source of ionizing radiation which is Americium-241, Figure 5. When alpha particles are generated by the Americium-241, they ionize the oxygen and nitrogen atoms of the air in the chamber. Ionization is a process of taking/breaking electrons of an atom, and when that happens, free electrons get attracted to an electrode with a positive voltage. Positive charges will be attracted to the electrode with a negative voltage. When smoke enters the ionization chamber, it disrupts this current flow, the smoke particles neutralize the ionization process which make it less conductive and lead to less current flow. The smoke detector senses the drop in current between the plates and sets off the alarm [8].
Figure 5

Ionization chamber

3 The Designed Device

The device is designed to turn off the stovetop before the initiation of the fire. In a normal scenario, the kitchen attendant will turn OFF the stove as soon as he/she hear the smoke detector alarm. The device will use the same idea but will assume that the kitchen is in unattended cooking scenario. Figure 6 shows the connection from the designed device to the smoke detector and the stove.
Figure 6

Connections between smoke detector controller and stove

The function of the controller unit is to receive a signal from a smoke detector, process it and control the power that flows to the stove. The controller unit will then turn off the stove as soon as it receives signal from the smoke detector of a fire hazard. The presence of smoke has been assumed to be the indication of the onset of an ignition flame. When a smoke detector detects the presence of smoke, the alarm goes off and simultaneously sends signal to the controller unit which will process the signal and shut off the power to the stove. The designed device uses the photoelectric smoke detector because of its advantages that are suitable for kitchen environment as mentioned earlier.

3.1 The Controller Unit Circuit of the Designed Device

Figure 7 shows the full circuit diagram of a control unit (smoke detector included) of the designed device that will detect and cut off the power to the stovetop in case of approaching fire. In the presence of smoke, the smoke detector will send a signal to the input of the control unit and drive piezoelectric that creates loud noise. The electrical signal sent by smoke detector to control unit is about 9 V, 400 Hz square wave signal as shown in Figure 8.
Figure 7

Designed circuit diagram for the device

Figure 8

Input signal

Basically, the designed controller unit itself is a switching circuit; once it receives a signal from the smoke detector it will process the signal and decide whether to shut off the power that goes to the stovetop or not. In the presence of smoke, smoke detector alarm will go off and generate 9 V 400 Hz electrical signal from smoke detector, which will be sent to the controller unit input and rectified by passing through diode D1 as shown in Figure 7.

After passing through the diode D1, the signal will be positive half cycle, which also shows lower signal amplitude than it was before rectification, 9.70 V (see Figure 8). Figure 9 shows the reduced signal of 5.40 V after rectification.
Figure 9

Input signal after rectification

The signal then travels to filter circuit known as RC circuit. The RC circuit will smooth out square wave signal to adequate DC lever capable of triggering the switching transistor Q1. The value of the resistor and capacitor in RC circuit were obtained using Equation 1.
$$ RC = \frac{1}{2\pi f} $$
(1)
where R is resistance in Ω, C is capacitance in microfarad, and π is 3.14, and f is frequency in Hz. Frequency is known to be 404.5 Hz (Figure 8), which is a signal frequency driving piezoelectric. The switching transistor (2N 2222) will switch 12 V to the relay #1, Figure 7. The relay #1 will switch relay #2 by sending 120 V to the relay #2. The relay #2 is the one that will allow power to go to the stove as well as cut the power to the stove.

3.2 Testing the Device

The device was tested using three different scenarios. The first was done simply by pressing the smoke detector test button. After pressing the test button, the alarm from the detector went off and simultaneously signaled the control unit to shut OFF the stovetop. The second test was done using a smoke detector tester where smoke was created from a tester and triggered alarm from a smoke detector. Upon receiving the alarm signal the control device was able to cut power supply that goes to the stovetop. The third test was done in the kitchen area, whereby the device was connected to the smoke detector and the stovetop (turned ON). Smoke from a burning pot was able to shut the stove OFF as soon as the alarm from the smoke detector went off. In all three scenarios, the controlled device was able to effectively cut off the power supply to the stove before ignition.

In the present study, the photoelectric smoke detector was used because it causes less (~5%) false alarms compare to the ionization smoke detector [1]. Further, photoelectric smoke detectors are inexpensive and are available in the local market; if project will be a success then every consumer can afford one. Lastly, smoke detectors are less complicated, more durable and requires less maintenance compared to other means of sensing device. In the similar study conducted by NIST, it was also stated and concluded that standard household photoelectric and ionization smoke detectors identify pre-ignition condition well (95% and 81% respectively) [1]. The only problem with smoke detectors is that it could generate false alarm, which can be reduced significantly if we incorporate the motion detectors as explained in the Section 6 of this paper. For more detailed testing, specifically on photoelectric detectors time response and performance refer to the National Institute of Standard and Technology [1].

4 Device Specifications

The device is designed to work in the kitchen environment with connections to a nearest receptor of the stove and linked to a smoke detector. The device is meant for domestic applications only with 15 Amps single burner stove. However this device can be easily extended to accommodate 240 V at 40 Amps. Table 1 shows specification summary of the designed device under normal conditions that the design product is capable to work effectively.
Table 1

Specifications of Designed Device that Receive Signal From a Smoke Detector

Parameters

Specifications

Normal

Input voltage (signal from detector)

5–10 V

9 V

Input frequency (frequency from detector)

300–900 Hz

400 Hz

Supply voltage

115–120 Volts

120 V

Supply current

15 Amps Max

15 Amps

Output voltage

115–120 V

120 V

Output current

15 Amps Max

15 Amps

Temperature

10–60°C

~28°C

Output phase supply

Single

Single

Receptacle type

15 Amps Duplex

15 Amps Duplex

DC supply voltage

15 V

12 V

This device can also be easily extended to accommodate any custom requirements. For example, it is possible to accommodate 30 Amp two or four burner by adding a second identical output relay #2. The device is capable of accommodating two phases by the addition of a second relay. This implies that the device can also be used for a four burner stove.

5 The Complete Device

Figure 10 shows the photograph of a completed device connected to a smoke detector and ready to use, whereas Figure 11 shows the internal view of the device. The device is divided into four parts internally: A, B, C, and D. Part A is 120 V/30 Amps relay. This relay will allow or cut the power that goes to the receptor in part B. Part B is the receptor where the stove is plugged. Part C can be considered as the brain of the device, where signal from the smoke detector is processed and triggers the relay in part A in the event of smoke.
Figure 10

The device connected to a smoke detector

Figure 11

Inside the device

6 Conclusions

The majority of all the residential fires established through the study are related to kitchen fires with significant portion stemming from cooking equipment, most often a range or stovetop. Based on the literature review, this study also concludes that the use of control devices is not new or innovative in the sense that several patent cooking units have in-built ‘no fire’ sensors or thermostats that are designed to cut power supply when reached certain temperature to protect ceramic material for the stove. However, the major problem is the ease of verifying the effectiveness of these in-built systems and its ability to contribute to reducing the risk of kitchen fires. This is mainly due to lack of any study conducted to determine the effectiveness of in-built systems.

An external control device developed in this study eliminates the short-falls and ineffectiveness of these in-built systems. The photoelectric smoke detector was used to design the device instead of ionization smoke detector due to its advantages of being suitable for kitchen environment and fewer false alarms than the ionization smoke detectors. The designed device showed promising results after several tests conducted both in the laboratory and a real kitchen environment.

To conclude, in this research a device was designed to control the fire incident which occurs mostly in the kitchen area. The device was designed in such a way that it will turn off the stove once smoke is sensed by a smoke detector. To achieve 0% false alarm results, this study could be extended in the future, for example by adding more application to the device such as motion sensors and/or thermocouples.

Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  1. 1.Faculty of ScienceCarleton UniversityOttawaCanada
  2. 2.Department of Civil and Environmental EngineeringCarleton UniversityOttawaCanada

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