Fire safety in kitchens of Chinese restaurants will be discussed in this paper. The licensing requirements and legislation aspects are outlined first with the past fire records briefly discussed. As identified, most kitchen fires in Chinese restaurants started from ‘cooking woks’ at the stoves. For assessing the thermal environment in a kitchen, heat release rates in burning such ‘woks’ in accidental fires should be measured. Two scenarios of burning woks with cooking oil were identified. The first scenario is a stove arrangement with only two woks . The second one is with six woks f or serving banquet. Full-scale burning tests on those two identified scenarios were carried out at a remote area in Northeast China. The heat release rate was measured by the oxygen consumption method. As sprinklers and water mist systems are commonly in stalled, the action of the sprinkler and water mist system on the cooking wok fires we re also studied. The times of fire extinguishment upon discharging the water mist were also reported in evaluating the protection system. These experimental results woul d provide useful information for future designs of fire safety provisions in kitchens of large hotel groups in the Far East. Keywords : heat release rate , accidental fire , fire safety , Chinese kitchens 3 1. Introduction Consequent to many uncontrollabl e large fires in buildings, tunnels and subway stations, fire safety in public areas in t he Far East is a concern. Hotel fire safety is now a hot issue due to the rapidly developing tourist industry in this part of the world with high density cities. Hotel fires happen everywhere including big cities like Hong Kong [1]. Most of them were con trolled by the hotel staff, or with the sprinkler system operated. These fires occurred due to poor maintenance or low quality electrical installation and appliances in the guestrooms, kitchens and laundry areas. Kitchens in hotels are considered areas w ith higher fire risk [2 -4]. Gas stoves with high thermal power are installed in Chinese restaurants [5]. Some of them are illegal alterations of gas installations by increasing the gas flow rate without approval from the Authority. Such high thermal powe r is necessary to heat up the ‘woks’ (Chinese pans) quickly to prepare higher quality of food with ‘wok -hay’ (i.e. gases, steam and sometimes flame generated by dipping fresh food in hot oil with alcohol in the wok, a term to determine the quality of Chine se food). Such high power cooking woks might give rise to kitchen fires when the cooking oil inside is heated up above the auto -ignition temperature. New regulations ar e to be set up in some areas but this would take time for carrying out the associated research and development studies. It is a long procedure in going through the legislation bodies requiring several years. Fire risk is usually specified in fire codes [e .g. 6] by the fire load density (FLD), the total amount of combustibles stored per uni t floor area . The upper limit of FLD is 1135 MJm-2 in some cities 4 [6]. As the kitchen is small with high FLD, flashover would occur rapidly. Large amounts of heat and smoke would be produced and spread out to other areas . The space adjacent to the kitchen such as the dining hall would be affected as investigated before by zone models [5,6] . However, FLD itself is not sufficient to quantify fire risk. The fire scenari os in a kitchen have to be identified for hazard assessment. Heat release rate [7,8] is the first parameter to assess the consequences of the identified fire scenarios. It should be calculated accurately with updated theory and new instruments. There are not many such studies on heat release rate for kitchen fires in the literature. It is necessary to understand the probable heat release rates in an accidental fire of kitchen in a Chinese restaurant , before demonstrating the associated standards are applicable [9 -11]. A series of full -scale burning tests were carried out to investigate the heat release rate of two different fire scenarios identified. Typical kitchens with woks and cooking oil commonly arranged in hotels were studied. The experiments were conducted in an experimental facility [5,12] at a remote town in Northeast China. Heat release rate was measured by oxygen consumption calorimetry [13,14]. Note that fire suppression systems are required in large commercial kitchens [2,6,9 -11]. Sprinkler systems are commonly installed in such kitchens in many big cities [6]. Applyin g water spray to cooking pans and stoves might give adverse effects. New fire suppression systems such as water mist system [15 -19] are acceptable. However, their perfo rmance in controlling fires from Chinese woks is not yet studied. 5 A sprinkler system and a low -pressure water mist fire suppression system were installed in the kitchen model . The cooking oil fires under the operation of sprinklers and water mist systems were studied. Effects of operating those water systems on the resulting heat release rates can then be evaluated. 6 2. Licensing Requirements Fire safety in the kitchen of a restaurant has to be provided by following the local codes. Taking Hong Kong as an example, a restaurant should obtain a restaurant license before its operation as specified in Chapter 132 Public Health and Municipal Services Ordinance Part IV [2 0]. In order to obtain a license, the design should comply with hygie ne requirements and the fire safety standards. Fire safety in tw o areas should be pro vided :  Passive sa fety measures of the restaurant including the structural design, compartmentation, and means of escape [2 1-24].  Active fire protection system [ 6,25] on at least four main areas: the fire service installations (in fact, these are active f ire engineering s ystems) , the usage of fuel, ventilation, and the means of access for fire fighters. Fuel storage and the type of fuel used will be controlled to minim ize the fire risk [2 6]. Normally, town gas, diesel oil and liquefied petroleum gas (L PG) are allowed. If diesel oil is used as fuel, it should be stored in a separate fire resistance chamber with an amount less than 500 litres [2 7]. In following local fi re regulations [6,2 5] and subsequent hotel license requirements [2 8] for restaurants a nd kitchens, fire service installations are required. Sprinkler systems with fast response or higher temperature response heads are required. In addition, water mist an d gas protection systems with clean agents such as heptafluoropropane are allowed. How ever, performance of the suppressio n system on kitchen fires is not yet evaluated. Such studies are necessary to support the specifications of fire safety provisions . 7 3. Kitchen Fires From the statistical records on restaurant fires compiled by the local Fire Services De partment [e.g. 1], most fires occur red in the kitchens. Very high thermal power stoves operated by either town gas or diesel oil were equipped for ensuri ng the quality of food. The major causes of fire were due to cooking appliances, elec tric faults and smoking materials. Over 50% of restaurant fires were originated from stoves as illustrated from the fire records. It is necessary to study cooking oil f ires in Hong Kong [5] . About 50% of all accidental fires in hotels, restaurants and f ast food outlets started in the kitchen involv ing cooking oil or fat fires [3]. As described [3], t he fuel temperature can reach up to 400 C for a cooking oil or fat fi re and the auto -ignition temperature varies from 285 C to 385 C. The fuel temperatu re of convention al test fires for Class B such as a heptane fire is only 50 C. Therefore, the cooking oil or fat fires are difficult to extinguish and easy to re -ignite , different from conventional liquid fuel fires. A new fire classification, Class F, is defined by some standard institutions such as the National Fire Protection Association, the British Standards Institution and the International Standards Organization [3,4] . It is different from the conventional class B liquid fires due to the high temp erature involved . Automatic sprinkler systems are generally installed and designed according to the common rules for automatic sprinkler installations as specified in th e code [ 6]. Sprinkler systems should be designed to deal with Ordinary Hazard I as re staurants are cl assified under this hazard. The normal operating temperature for sprinklers in commercial buildings is 68 C. This type of 8 sprinkler is suitable for inst allation in the dining halls of restaurants. However, sprinkler heads with higher act uation temperatu re such as 79 C, or a longer response time index should be considered in kitchens. It happened before that sprinkler heads above the stove w ere actuated by the hot ‘wok -hay’! There is an increasing use of water mist system for kitchens [e .g. 15-19]. Water, carbon dioxide, halon gas (in the past) and powder types of extinguishers are commonly used. 9 4. Oxygen Consumption Calorimetry Heat r elease rate can be measured [2 9] by the sensible enthalpy rise method, substitution me thod, compensation method and o xygen consumption method. Oxygen consumption method is now widely used [7] in bench -scale experiments such as the cone calorimeter, medium -scale rigs such as the furniture calorimeter and single burning items test, and full -scale burning tests such as the room calorimeter. All target to get some information on real fires. The concept was proposed by Thornton [13], and then developed later b y Huggett [14] with rapid development of accurate gas sensors. The mass loss rate of o xygen for burning is measured f irst. The heat release rate can be estimated by multiplying it with the heat generated by burning a unit mass of oxygen for that fuel (simi lar to the calorific value for the heat generated per unit mass of fuel burnt). The he at generated per unit mass of o xygen consumed appears to be a constant for all normal fuel, about 13.1 MJ/kg oxygen consumed with 5% accuracy. An exhaust hood with a f an-duct should be constructed to collect the flue gas generated by the burning process . The heat release rate can be estimated by the oxygen consumption rate in the incoming air. The equations for calculating heat release rate by the oxygen consumption me thod were discussed by Parker [30 ,31] and Janssens [3 2] and Dlugogorski et al. [33]. For complete combustion, the equ ations concerned will be relatively simple. The heat release rate Q (in kW) is given in terms of the mass flow rate of oxygen in the incoming air o Om 2 (in kgs-1), the mass flow rate of oxygen in the exhaust gas 2Om (in kgs-1) and the universal constant E as follows, 10 ) ( 2 2 Oo Om mE Q  −= (1) However, incomplete combust ion is lik ely in the fire tests . Concentrations of other species such as carbon dioxide and car bon monoxide have to be measure d for accurate calculations. For convenience, condition of incoming air for burning is assumed to be the same as ambient air. Concentratio ns of oxygen, nitrogen, carbon dioxide and water vapour are constant. Carbon monoxide in the incoming air oA COX is not included. Carbon dioxide concentration in the air o COX 2 is approximately 330 ppm. Water vapour in the air o OHX 2 is calculated in terms of the relative humidity, ambient te mperature, ambient pressure and saturation pressure of water vapour at that temperature. When only oxygen is measured, both water vapour and carbon dioxide should be r emoved before measuring oxygen. The mole fraction of carbon monoxide is taken as zero . The equation of heat release rate Q is given by: oA Oo COo OH aO eX X X MM mEQ 2 2 22) 1( )1 ( 1−− −+=  (2) The oxygen depletion factor is given by: oo A OA OA OA O X XX X 2 22 2 ) 1(−− = (3) The expansion factor  is measured to be 1.105 for common burning fuel. 11 Equati on (2) based on only measuring oxygen is the most commonly used e quation . It is easier to carry out the test with only an oxygen analyzer. However, high values of error a re expected f or burning with high concentration of carbon monoxide and soot released. The oxygen consumption method might require some modifications on heat release rate measurements for specific circumstances as in fire suppression experiments. Part of the heat is taken away due to vaporisation of water mist . This should be taken into account [33] by including percentage of water. However, water content was not measured in the tests due to resources limitation. This would be key issue to get valid m easurement in fu ture studies. 12 5. The Kitchen Model To assess how sprinkl er and water mist would control a fire, ful l-scale burning tests were carried out. Kitchen fire scenarios with and without the operation of sprinklers and water mist sys tems were considered. A full -scale burning facility for measuring heat release rate i n different building arrangement was develo ped [12] in a remote town Lanxi, about 150 km from Harbin, Heilongjiang, China. A model Chinese kitchen with an exhaust hood a nd a fan -duct system as in Fig. 1 was constructed with flashover kitchen fires studied . Cooking oil in the woks over the stove was burnt. Heat release rates were measured by the oxygen consumption method [7,13,14]. Result s on the heat release rate are useful for fire hazard assessment on kitchen fires on agreeing an ‘initial design fire ’ at the starting -up stage. The experiments do not involve other fuel that may be ignited and contribute to the fire. As noted by the authors, kitchens have high fuel lo ad density. A starting fire can quickly spread to involve items other than the ignitio n source. Results on heat release rate from this study are useful for studying consequences of different scenarios with fire models. The two identified scenarios were typical setups in Chinese restaurants in hotels:  Burning cooking oil in two woks in a gas stove for a staf f canteen. Two woks will be used in serving meals for staff canteen under normal operation. The cooling oil in the woks was burnt.  Burning cooling oil i n six woks in a large banquet. In serving banquet in a hotel, six woks will be used to prepare food qui ckly for 1200 persons, usually 100 tables with 12 persons per table. 13 6. Full-Scale Burning Tests Two groups of six kitchen fire tests were carried out a s follows: (i) Group A arrangement on a kitchen for a Chinese restaurant functioning as a hotel staff canteen with two woks: Such an arrangement is shown in Fig. 1a. Each wok was filled with 1000 ml soyabean oil. Three scenarios were considered:  Test A1: Fire only.  Test A2: Fire with the operation of water sprinkler system.  Test A3: Fire with the op eration of water mist system. (ii) Group B arrangement on a typical large r kitchen of a Chinese restaurant for banquet with six woks: Each wok was fille d with 1000 ml of soyabean oil as in Fig. 1c. Three scenarios were identified:  Test B 1: All six woks on fire.  Test B2: All six woks on fire with the operation of water sprinkler system.  Test B3: All six woks on fire with the operation of water mist system . The kitchen model is of length 3.6 m, width 2.4 m and depth 2.4 m as shown in Fig. 2a. Flue 14 gas li berated would be extracted by a fan -duct system through the exhaust hood at a door opening of width 0.8 m and length 2 m. A stainless steel table long eno ugh to set up six woks and two sinks was constructed as in Fig. 2b. The woks filled wi th oil were igni ted as shown in the photograph s. Tests were then repeated by operating the sprinkler system and the water mist fire suppression system. The operating pr essures were 1.12 MPa and 1.26 MPa; and flow rates 5 l/s and 0.2 l/s respectively for the two systems. Note that the flow rate of the water mist system was only 4% of that for sprinkler. Ambient air temperature s were from 18 oC to 22 oC, relative humidit ies from 50% to 90% while carrying out the experiments from July to September in 2005. Results on oxy gen co nsumption and heat release rate are shown in Figs. 3 and 4. 15 7. Results on Group A Tests Two woks filled with soyabean oil as in Fig. 2c were tested.  Test A1 Smoke was generated when the oil was heated. After about 7 min after ignition , the oil was ignited. A sharp increase in heat release rate is shown in Fig. 3.  Test A2 After the gas stoves were lit, it took 4 min 55 s and 7 min 54 s r espectively for the cooking oil to be lit at pan A and B. The sprinkler system wa s turned on after 9 min 50 s. No splashing or spillage of oil was observed. The fire was extinguished after 10 min 1 s. The total extinguishing time is 601 s. The heat re lease rate is also shown in Fig. 3.  Test A3 After the gas stoves were lit, it too k about 6 min 13 s for the oil to be ignited. The gas valve was then shut. After another 2.5 min, the water mist system was activated. It took 16 min 7 s for the water mis t system to extinguish the fire. The total burning time is 25 min 20 s but burning with a very small f lame at the later stage . The refore, only part of the heat release rate curve is shown in Fig. 3 for comparing with other tests. 16 8. Results on Group B Tests All six woks as in Fig. 2d were burnt.  Test B1 It took 6 min 20 s for fire to be ignited at wok A1, 6 min 35 s at wok A2, 4 min 45 s at wok A3, 5 min 34 s at wok B1, 5 min 10 s at wok B2 and 6 min 10 s at wok B3. The fire was extinguished after 9 min 14 s at wok A1, 15 min 59 s at wok A2, 13 min 30 s at wok A3, 8 min 50 s at wok B1, 8 min at wok B2 and 16 min 10 s at wok B3. The heat release rate is shown in Fig. 4.  Test B2 It took 5 min 32 s for fire to be ignited at wok A1, 6 min 20 s at wok A2, 7 min 16 s at wok A3, 6 min 27 s at wok B1, 6 min 11 s at wok B2 and 6 min 37 s a t wok B3. The water sprinkler system was activated 8 min 7 s after the gas stove was lit. No splashing or spillage of oil was observed in test A2. Water discharge was s topped at 8 min 20 s. The oil was re -ignited and water was turned on again at 8 min 57 s. The cooking oil fire was completely extinguished at 10 min 50 s. The heat release rate is shown in Fig. 4.  Test B3 17 It took 6 min 14 s for the fire to be ignited at wok A1, 7 min 5 s at wok A2, 7 min 9 s at wok A3, 6 min 27 s at wok B1, 6 min 35 s at wok B2 and 6 min 40 s at wok B3. The water mist system was activated at 9 min 33 s after the gas stove was lighted. It took 19 min 3 s to extinguish the oil fire. T he heat release rate is shown in Fig. 4. 18 9. Discussion Six tests wer e conducted in a sample kitchen with two or six woks burning. On group A arrangement with two woks burning, the environment was quite smoky in test A1. The maximum heat release rate went up to 0.4 MW. In test A2, the sprinkler system needed less time, w ithin a total d uration of 20 min, to extinguish the fire complet ely for the same setup. In test A3, the water mist system was effective in extinguishing the fire in abou t 25 min. Time for extinguishing the fire was only 4% of the extinguishing time recor ded for sprinkl ers. On group B arrangement with six woks burning, the maximum heat release rate was up to 1.4 MW for test B1 . On this particular test, flame moved out of the door, satisfying one of the criteri a for onsetting flashover. Equations derived on estimating maximum heat release rate mfQ in flashover were reviewed and compared [ 34]. The equation by Thomas et al. [35] on mfQ agrees well with experiment in this room calorimeter. It is related to ventilation factor v vH A , where A v and H v are vent opening and height respectively as: T v v mf A8.7 H A378 Q + = (4) AT is the total area of room which depends o n room length L of 3.6 m, room width W of 2.4 m and room height H of 2.4 m minus the ventilation open ing area Av given by: AT = 2(L+W)H + 2LW – Av (5) 19 AT is 44.48 m2 and therefore mfQ is 1.2 MW given by equation ( 5). The measured 1.4 M W is over t hat and so flashover should be onsetted with flame moving out . In test B2, the sprinkler system took less time in comparing with test B3 with water mist system to extinguish the fire . It appears that water mist under the design condition is not as effective in suppressing bigger wok fires. The operation effect of sprinkler syst ems and water m ist systems on burning cooking oil in woks on stove were studied. This would give some indication on how the fire suppression system would perform on the starting up fire. Both water systems are effective in extinguishing the fire rapidly. From the above preliminary tests, it appears that the sprinkler system is efficient in extinguishing the fire. No splashing or spillage of fuel was observed for the wok arrangements in the kitchen model. However, more water is required in operating the sprinkler syste m. For a 3 m cubic room rated as ordinary hazard class, the water flow rate for a sprinkler head is 45 litres per minute to give a water discharge density of 5 mm per minute in the protected area . The flow rate for a water mist nozzle in a low pressure suppression system is down to 5.4 litres per minute as the required water density is only 0.2 litres per minute per m3 of space volume . The time s taken by t he sprinkler and water mist systems measured in above are not taken as a n extinguish t ime in a real k itchen fire as other fuel s and combustibles are not involved . It is interesting to observe that the water mist system controlled the fire at about the same heat release rate as the sprinkler system in the case of the six wok fire . In the ca se of the two w ok fire, the heat release rate under action of water mist was even significantly higher than on operating the 20 sprinkler system. Higher heat release rate i n using water mist system was measured due to initial expansion of flame volume upon operating the sy stem. Such extinguishing mechanism s on starting up fire would be studied in the future by inc luding chemical s uppressing reactions of water mist on the pa rticular fuel type. 21 10. Conclusions Fire safety in hotel kitchen s in Hong Kong [5] was discussed with the code and licensing requirements reviewed. Heat release rates in burning woks in Chinese restaurants were studied by six full -scale burning tests on two identified scenarios. Two different wok arrangements in a ki tchen model in Chinese restaurant were set up in a remote area of Northeast China. The heat release rate was measured by the oxygen consumption calorimetry. As observ ed, a wok fire might be developed to onset flashover in the kitchen. The heat release rate would increase to give bigg er fires. Fire suppression systems must be installed. Both sprinkler and water mist systems are demonstrated to be effective in exting uishing the fire under the tested scenarios. However, different kitchen geometries wi th different wok arrangements wou ld give different fire environments. Procedures in designing fire suppression systems for local kitchens in this part of the world shoul d be modified [9 -11] from overseas studies. Similar tests are recommended to confirm the performance of the systems. This is particularly important for open kitchens in small residential units of very tall buildings [36]. Obviously, cooking with woks is n ot allowed in those open kitchens. 22 11. Additional Comments The paper was pub lished as a journal paper [ 37]. With the p ractice of publisher, preprint i s allowed to upload at a website. There are furth er studi es on this topic [ 38-56]. 23