TUNNEL VENTILATION SYSTEM FOR THE UNDERGROUND CORRIDOR OF DELHI MASS RAPID TRANSIT SYSTEM

Transcription

1 TUNNEL VENTILATION SYSTEM FOR THE UNDERGROUND CORRIDOR OF DELHI MASS RAPID TRANSIT SYSTEM Satish Kumar, Director Electrical Sharat Sharma, General Manager Electrical Delhi Metro Rail Corporation 1 INTRODUCTION Delhi Metro Rail Corporation Limited, (DMRC) has been set up for the implementation and operation of Delhi MRTS project. In order to facilitate the transportation need for the people of Delhi, an MRT system of approx. 200 km has been envisaged by the end of completion of phase-ii by Of which, 32 km will be the underground (Metro Corridor) section. An underground corridor on Yellow line from GTB Nagar to Saket is around 24 kms long with 20 underground stations. The other metro corridor from Central Secretariat to Badarpur of line-6 is about 4.5 km long and will have 4 underground stations. The third existing metro corridor is 2.5 km long existing metro corridor from Rajiv Chowk to Mandi House having 3 under ground stations. Thus by the end of Phase-II, DMRC will have 32 km of underground section with 27 stations, besides 16 km of underground section of Airport link with 5 underground stations, which will be operated through the Concessionaire. 2. DESIGN CONSIDERATIONS OF TUNNEL VENTILATION SYSTEM: The considerations for the comfort and safety of commuters in the subway area i.e. underground stations and tunnels is of significant importance, keeping in view that a large number of people are transported through a confined space, which does not have full natural ventilation. The ambient temperature in the city varies between 2ºC in winters to as high as 44ºC in summers. In addition, today's state-of-art modern-rolling stock provided with air-conditioners dissipates substantial heat inside the subway. This results in the hot air entry into the platform of the underground Stations. The environmental conditions inside the subway need to be maintained within the comfort levels irrespective of these extreme ambient temperature conditions. The design criteria and performance of the Tunnel Ventilation System, thus, greatly influences the comfort of patrons and hence the success of any MRT system. Apart from the comfort requirements inside the subway, the issue of fire and life safety of the passengers assumes greater significance. The evacuation pattern in the event of fire emergency is an important design issue for any underground MRT system. This paper deals with the subject of Tunnel Ventilation System studies and approach leading to the design for the underground section of Delhi Metro. 3 ENVIRONMENTAL CONDITIONS; For the underground corridor, great emphasis has been laid on proper selection of design parameters, ambient condition, system and equipment right in the design stage itself. a) Optimum Design; During the summer the temperature in Delhi reaches maximum up to 47 ºC. However, this temperature occurs during the afternoon i.e. non-peak hours when stations are not heavily occupied. As for the MRTS the traffic peaks during the morning and evening rush 183

2 hours. Therefore, in order to design optimum capacity and save energy, it is preferred to adopt 1% design criterion. This implies that the design temperature shall not be exceeded for 99% time during summer season. For Delhi, the 1% design conditions are 43 ºC (DBT), 28 ºC (WBT). Similarly, the design condition for monsoon season has also been optimized. Based on this the design criterion outdoor temperatures are chosen as under:? Summer 43 ºC (DB) 28 ºC (WB)? Monsoon 35 ºC (DB) 29 ºC (WB) In winter instead of heating, free cooling has been resorted to. This implies that the heat released by various equipments will be adequate to maintain acceptable conditions inside the subway. Hence there is considerable energy saving on VAC system during the winter season. b) Choice of Acceptable conditions inside coaches and station areas In an MRTS station passengers are not expected to wait for longer durations and therefore they would not reach a thermal steady state with respect to the environment. Relative Warmth index (RWI) is the widely recommended thermal index for subway environmental control. In order to keep the RWI values within 0.4 and 0.45 the design conditions for the platform area has been prescribed as 29 ºC and 65% RH. The condition inside the coaches have been stipulated to be 27 ºC with 65% RH. These conditions, fall within the borderline of comfort zone and the passengers would feel comfortable as they face a graded environment from outside to the station and then to the coaches. By selecting these design conditions the cooling capacity has been optimized thereby reducing the initial cost as well as the recurring energy cost of operation and maintenance. The summer and monsoon ambient temperatures are to be used for the design of the tunnel ventilation and air-conditioning system at the station. The design dry bulb temperature for the public area within DMRC existing station is 290 C with 65% humidity in phase-i and 270 C with 55% humidity in Phase-II under construction. There are four system operating modes for the tunnel ventilation system in normal operation depending on the outside ambient conditions of Delhi. Hot: Vent shafts closed, full recirculation, minimum outside air, Air-conditioner operating Warm: Vent shafts open, 100% outside air, Air-conditioner operating. Cool: Cold: Vent Shafts open. 100% outside air, Air-conditioner off. Vent shafts closed, no TES, no Air-conditioner In DMRC the air-conditioners remains off from 15th November to 15th February. 4 MODE OF OPERATION The 'Open System' requires the tunnel ventilation and station air conditioning system to use 100% outside air. In Open System all tunnel ventilation shaft dampers are wide open to permit a free exchange of air between the tunnels and the surface during the train running. The design selected for the 'Tunnel Ventilation Systems' of DMRC is commonly referred to as the 'Closed System' concept. In a Closed system the ventilation shaft dampers are closed and tunnel air is re-circulated to the station air conditioning system. 184

3 For the summer and monsoon design conditions, the enthalpy of the air entering the station air conditioning system from the track way owing to piston effect of the train is considerably less than that of air entering the system from outside environment. This translates into a reduced air conditioning system capacity and hence the operating cost. 5 OBJECTIVES FOR TVS DESIGN The Tunnel Ventilation System (TVS) is intended to provide:? An acceptable environment in the tunnel and station track way for the operation of trains;? 'Normal operation' - Air pressure relief? 'Congested Operation' or Maintenance - Heat removal.? 'Emergency operation' - An effective means of controlling smoke flow, to ensure smoke free path for both patrons and employees during evacuation and fire-fighting personnel access to reach an incident location without traversing a smoke-filled path.? Acceptable environmental conditions in the stations so that the patrons and equipment would not suffer from any adverse effects. 6. DIFFERENT OPERATING SCENARIOS The Closed system for tunnel ventilation is described in the following text by way of its application to the three operating scenarios: Normal, Congested and Emergency. 6.1 'NORMAL OPERATION' is when the trains are working to timetable throughout the system, at prescribed headways and dwell times, within given tolerances. The piston-action of trains moving through confined tunnel space is a natural resource for the 'Normal Operation' ventilation. The key parameter in determining the effectiveness of the piston-action is the blockage ratio i.e. the vehicle cross sectional area/ tunnel cross sectional area. The greater the blockage area, the larger is the pistoneffect. The general reduction in the tunnel air temperature that will be achieved by this ventilation plan will benefit vehicle air-conditioning systems, station air-conditioning systems, and passenger comfort. As the train travels inside the tunnel, the heat released from the train will increase the tunnel temperature. At the same time, tunnel air is pushed by piston effect of the moving train in the travelling direction. Therefore, the tunnel temperature profile is gradually increasing in the train travelling direction. The temperature will depend upon? Length of tunnel? Train propulsion and braking performance? Coasting operation? Heat Sink effect - Sub Soil Temperature The environmental simulation studies of the train operations indicated that the tunnel temperature might rise to 40ºC temporarily and hence if the sub-soil temperature is relatively low than there is possibility of the soil with huge mass working as a heat sink. The stabilized underground temperature of the soil in Delhi has been measured at various depths on different locations for a period of two years by using sophisticated thermocouples. The average temperature as recorded is found to be 29 ºC. The tunnel 185

4 ventilation system has been designed such that the deep soil is not used as a heat sink, thereby increasing the soil temperature in future and cause imbalance to the environmental control inside the subway. Relief of train generated piston action air will be through bypass shafts that permit the air to be exchanged between the UP line and Down Line tunnels. Pressure relief is provided through the ventilation shafts and cross connections at each end of the station, and across the platforms themselves. Track way extract System (TES) is installed in the track ways of each station to capture both excessive tunnel airflows and the heat rejected by the vehicle propulsion/braking/air-conditioning systems as the train dwells in the station. An under Platform Exhaust (UPE) duct is often utilised to capture heat from the trains undercarriage heat sources. An Over Track Exhaust (OTE) duct is normally utilised to capture heat that is rejected from the rooftop mounted air-conditioning units from the cars. Openings in the OTE and UPE are located so as to be near the heat generating sources on the train. The combined efficiency of TES is defined as the ratio of the train heat directly captured by the system before it can mix in the train way to the total heat released by the train as it dwells in the station of the system is at least 65%. During summer and monsoon, when the station air conditioning is operating, the TVS will be set in a Closed arrangement, in which all tunnel ventilation shaft dampers will be closed and the air captured by the Track way Exhaust System (TES) will be re-circulated to the station Air Handling Units, where it is mixed with the ambient fresh air in a fixed proportion. During temperate or cold outside conditions, such as, spring, autumn and in winter, or anytime when the station air-conditioning plant is shut down, the tunnel ventilation shafts dampers will be opened and the Track way Exhaust System (TES) will discharge the station air directly to atmosphere. 6.2 'Congested Operation' conditions occur when delays cause disruption to the movement of trains. It is possible that the delays may result in stabling of a train in a tunnel section. The excessive tunnel temperatures due to heat dissipation of Air conditioning units on the roof top of the cars may reach 46ºC in the vicinity of the condenser inlets, the airconditioning units are expected to begin unloading - a condition when the efficiency of the system is drastically reduced too the point that there is no more cooling effect and hence causing discomfort to the passengers on board. The recommended mechanical response for preventing the accumulation of warm tunnel air around idling trains is to provide and activate the Tunnel ventilation Fans at the required location. In the affected ventilation zone, the TVF's would be operated so that a steady flow of fresh air is passed over the idling train. The tunnel ventilation design condition for congested train operations is a maximum stratified tunnel air temperature of 46ºC. This temperature will be as measured near the inlets to the train AC units. Generally, the TVF fans required to run in the direction of the train travelling so the direction of air over the train to be ventilated can be maintained easily. In case of 'open Mode', TVF's are required to operate in a push-pull mode. To generate the push-pull 186

5 effect, one TVF of affected ventilation zone would be operated in the supply mode and the other TVF on the other end of the train in exhaust mode so as to move the air through the tunnel in the direction the train travel. 6.3 'EMERGENCY OPERATION' is resorted to when smoke is generated in the tunnel or station trackway from any variety of occurrences (including transit vehicle malfunctions or fires). In emergency conditions, the tunnel ventilation system is set to operate to control the movement of smoke and provide a smoke-free path for evacuation of the passengers and entry for the fire fighting personnel. The ventilation system is operated in a 'push-pull' supply and exhaust mode with jet fans or nozzles driving tunnel flows such that the smoke is directed to move in the desired direction, enabling evacuation in the opposite direction. Control over the direction of spread of smoke within the tunnel can be exercised if the operation of the TVS is sufficient to produce the critical annular air velocity to prevent smoke from back layering. While preventing back layering (and thus, controlling the direction of smoke flow) in the incident tunnel, the TVS must operate within three constraints: i) a minimum annular air velocity in the tunnel evacuation path, ii) iii) a maximum allowable air velocity of 11 m/s in the tunnel evacuation path and The maximum allowable temperature in the tunnel evacuation path must not exceed 60ºC. The DMRC train fire heat release rate is 15 MW, for the purpose of Fire Emergency calculations. With regard to emergency conditions, the success of the ventilation plan for tunnel fire relates directly to the growth of a fire incident. Therefore, the fire integrity of the vehicle components and the combustible content of the vehicle assume significance in emergency ventilation analysis. As per NFPA -130 section 7.2.1; the emergency ventilation system shall be designed to do the following; (a) (b) (c) (d) Provide a tenable environment along the path of egress from a fire incident in enclosed train ways Produce airflow rates sufficient to prevent back layering of smoke in the egress within enclosed train ways. Be capable of reaching full operational mode within 180 Secs. Accommodate maximum number of trains between ventilation shafts during emergency. Communication between the incident vehicle and the Train Service Regulator at the Command Center is vital because a timely response is needed from the Tunnel Ventilation System in order to preserve a smoke-free environment in the selected passenger evacuation route. Of the utmost importance is the identification of the exact fire location aboard an eight-vehicle train, as it determines the direction of airflow of the TVS and the passage of evacuation. In addition, the response of the TVS has to be coordinated with the removal of nonincident trains from the affected ventilation zone. Passenger evacuation, whether it is from incident trains, non-incident trains or from stations is in compliance with NFPA-130 guidelines. Finally, the high temperature rating of the ventilation equipment must be 187

6 assured so that axial-flow fans, dampers, etc. are capable of operation during extreme heat conditions. The operation of the TVFs for emergency tunnel conditions, like that of congested train operations, will be designed to generate a push-pull effect in the incident tunnel. Fig.: Train on fire in Tunnel 7 TUNNEL VENTILATION SYSTEM DESCRIPTION 7.1 Tunnel Ventilation Fan Two tunnel ventilation fans of capacities 75 m3/s to 100 m3/s are installed in each of the TVS Plant Rooms near vent shafts at each end of the station. The exact capacity, which is dependent upon topology of the section, X-section area of the tunnel size of fire and critical velocity etc, is obtained through the simulation. The total pressure the fan will need to over come is approximately 1500 Pa. TVF system is designed to control smoke flows in the tunnel during fire and limit the rise in tunnel air temperature during the congestion. Tunnel Ventilation Fan System is comprised of two large diameters, reversible TVFs to be installed in rooms adjacent to each Tunnel Ventilation Shaft. In addition to the fans themselves, the mechanical equipment components will consist of transitions piece, sound attenuators and dampers. Transitions piece reduce pressure losses and allow a reasonably smooth air velocity profile. Sound attenuators provide for noise reduction so as the operation of the TVFs is not audibly disturbing. Dampers are used to control the direction of overflow. There are tradeoffs between structure, fan system size and design. TVS system performance is governed by the requirements confirmed through the SES modeling. Fig.:- Tunnel Ventilation Fan 188

7 7.2 Track way Exhaust Fan System The TEF System fans are located in the concourse area of each station. Generally, three Trackway Exhaust Fans are installed on either end of each station track way (6 per station). The fan capacity required for each Trackway Exhaust Fan is of the order of 21 to 30 m3/s. The exact capacity is obtained through the simulation. The total pressure the fans are to over come is approximately 1200 Pa. In addition to the fans, the mechanical equipment components for the TES will consist of transitions, sound attenuators and dampers. Dampers are used to control the path through which the air will flow. When station air-conditioning plant is running the air collected by the TES is re-circulated to the station AHUs. During winter seasons, when the station air conditioning plant is turned off, the TES discharge directly to atmosphere. Fig.: Track way Exhaust Fans The TES fans operate in accordance with the TVF's during a fire in the station track way area to prevent smoke from entering the station platform area and affecting passenger's evacuation efforts. TES is designed in accordance of platform area and affecting passenger evacuation efforts. TES designed for heat capture during normal trains operations will also aid in the system wide emergency response effort. As stated, the TEFs run continuously during normal and emergency conditions. The three track way exhaust fans are interconnected with air ducts and isolation dampers. In case one fan fails to operate the other 5 fans can provide a minimum of 83% of the total air exhaust rate. UPE and OTE intake openings are located to coincide with train-borne heat sources, consist of train brakes, traction equipment and train air conditioning system condensing units etc. Each intake shall be fitted with a fixed bar grille and shall be provided with a means of balancing. Airflow at each intake shall be balanced to within + or - 10 percent of the design flow. All ductwork and supports will be capable of withstanding temperatures of 250ºC for one hour. The airflow is generally split on a ratio of 5:3 between the OTE Duct and the UPE duct. 189

8 7.3 TUNNEL BOOSTER FAN SYSTEM The installation and operation of TBFs may be necessary and important in moving air in the desired direction through the track way crossovers. The two TBF at each location are ceiling-mounted. In all cases, the TBF shall be such located that the discharge velocities do not impede the evacuation of people. The operating plan for the TBF's in the tunnel sections with lay-up tracks and crossovers is only applicable when incidents occur within these tunnel sections. The presence of the TBF's in the mainline tunnels is mainly due to the mechanical ventilating requirements during congested and emergency operations. The operating plan for the TBF's, therefore, is dependent upon both the location, as well as the nature, of the incident. The number of TBFs operating during a congestion/emergency incident should be coordinated with the operation of the TVFs. During congested train operations, both the TBF's in the incident tunnel should be operated in a direction consistent with the flow of fresh air - the TBFs are so operated to induce momentum onto this airflow and assure the delivery of fresh air to the congested trains. The TBF's in the non-incident tunnels are not operated during vehicular congestion. The TBF's in the incident tunnel should be operated in the direction of fresh airflow so that they may direct more fresh air past the incident location, but their performance and survival in close proximity of a fire incident cannot be guaranteed. The noise level of the TBF is governed by the announcements by the communication system which can be heard by patrons within the tunnel during emergency. 7.4 TUNNEL VENTILATION DAMPERS The fan dampers that are part of the tunnel ventilation fan system include track dampers, draft relief dampers, isolation dampers, nozzle dampers and shaft dampers. Draft relief dampers shall be situated to allow airflow between the track way and the surface during periods for normal operation. The fan dampers that are a part of the Track way Exhaust System are the TES. The use of a closed system requires the installation of two dampers in the duct that connects TES and AHUs. Fig. : Tunnel Ventilation Dampers 190

9 The TVF and TES dampers, like their corresponding fan systems, shall also be temperature-rated for use during emergency tunnel/station conditions. Pneumatically operated damper actuators are on reliability consideration. A mode table for damper operations during normal train operations, congested train operations and emergency tunnel conditions is developed. The table will, generally, show the recommended damper positions (open or closed) during the aforementioned modes of train operations. 7.5 Ventilation Shafts Draught relief shafts have been be provided for train piston action pressure relief and mechanical ventilation at each end of the station. The TES shafts will also carry exhaust air away from the station ventilation and air conditioning system. The terminal air velocity from relief shafts located in public areas would be exposed to the air-stream, shall not exceed 2.5 m/s, or else the terminal air velocity from relief shafts shall not exceed 5.0 m/s. 7.6 Tunnel ventilation Nozzles The nozzles are required mainly for two reasons; Firstly, the system arrangement in DMRC stations does not have Platform Screen Doors (PSD), hence both tunnel sections are interconnected with each other across the platforms and to atmosphere through station entrances. The station design is such that platform and concourse volumes are large and have many interconnections between them and to the surface and hence pressure conditions at the platform are affected by the atmospheric conditions. An attempt to direct air across stalled train would result in large volumes of air flowing through station and non-incident tunnel. This is likely to occur because the resistance to flow across the train in the tunnel is greater than it is through the stations or along the non-incident tunnel. To generate the required flow across the train with pressurization alone would require grossly oversized TVF fans. Nozzles provide momentum in the required flow direction. Secondly, the high ambient dry bulb conditions (43ºC for design) in Delhi demands closed mode operation. In the event of congestion when there are hot ambient conditions, it is not desirable to introduce the outside air for the ventilation. It is preferable to use cool station air for this ventilation. Use of a nozzle allows cool system air to be drawn from upstream of the nozzle and directed down the tunnel without recirculation. The hot air downstream station of the train is accommodated by the station cooling system. 8 NOZZLE EFFECTIVENESS The performance of nozzle is dependent on a number of parameters, including nozzle geometry. The geometry of nozzle at various locations in the system would vary due to constraints of location. The variations would include tunnel shape local to nozzle outlet (bored/cut and cover), nozzle inclination angle, location of nozzle outlet (rooftop/sidewalk) and outlet size and shape. Nozzle effectiveness describes the relation between the theoretical head a nozzle could develop and the actual head delivered. The nozzle effectiveness (factor) is not a critical design parameter. Following beta factor was observed for the three types of nozzle geometry which were used in Phase- I of Delhi MRTS. (i) Nozzle near the Cut and Cover tunnel: The nozzle is directed towards the cut and cover at an angle of 20o to the tunnel centerline. The beta factor can be estimated at ß=

10 (ii) (iii) Nozzle near the Bored tunnel: The nozzle is directed towards the circular tunnel bores at an angle of 15o to the tunnel centerline. The beta factor can be estimated at ß=0.948 Nozzle at a vertical plane corresponding to the tunnel walkway. The nozzle is directed the air from the side wall at a high level. The nozzle centerline is at 15o to the tunnel centerline. The beta factor can be estimated at ß= NOISE CRITERIA Noise level criteria will need to be developed for each station. Consideration will need to be given to local noise criteria and the placement of shaft outlets. Recommended maximum noise levels are as follows: Station's concourse, platform areas To boundary of nearest property To boundary of nearest building Equipment noise 55 dba 60 dba (7am to 11pm) 55 dba (11pm to 7 am) 85 dba within plant room These values are considered applicable during normal operation of the railway. During emergency or train congestion situations, which are considered special, the maximum noise level in the stations' concourse and platform areas are planned not to exceed 75 dba. Operation of one tunnel ventilation fan (per TV shaft) during Engineering maintenance hours after normal operation hours will be anticipated. The maximum external noise level as stated above will be complied with during this operation. 10 MID TUNNEL VENTILATION SHAFT The designed headway for the operation of DMRC is 2-minute in If the inter station distance is more than 1.5 kms there may be two train in the same tunnel, if trains are run as per the headway, requirement of having the one train in one ventilation zone or means of evacuation are to be provided. In the proposed metro corridor of phase-ii the inter-station distances are more than 1.5 kms at various locations, hence to split the ventilation zones into two zones, the mid tunnel ventilation system is being considered. 11 CONTROL AND MONITORING FACILITIES The tunnel ventilation system shall be completed and equipped with provisions for automatic, manual, local and remote controls so that the fans and motors can be operated from a station control center or from the Operations Control Center (OCC). The control system shall comprise of a local control system that shall interface with the other system. The TVS will normally be controlled and monitored from the OCC. At OCC, an Integrated Supervisory Control System (also referred to as SCADA System), will control and monitor the TVS plant in each station. The local control system for the TVS is designed to receive control commands from OCC, to control the TVS equipment to the desired conditions and report equipment status, including operation alarms, to the OCC through the SCADA system. The control philosophy shall embrace the provision for a multi-alternate facility having a hierarchy as follows: 1. Centrally, by main system control room at the Operation Control Centre This operation will be controlled via SCADA. 2. Centrally at each station from the Station Operations Room. This operation will be controlled via the local SCADA panel at the SOR 192

11 3. Override provision shall be made to provide for control by the fireman's control panel at each station 4. Locally at each tunnel ventilation plant room by operation of the Manual Off Auto switch The system shall be set-up for fail-safe operation such that under failure of controls power, the system shall operate as for Emergency Mode. Track way isolation dampers shall fail open and by-pass damper shall fail closed. Speed controllers, if fitted, shall be complete with full speed by-pass which shall be automatically energized in the event of a fault condition from the controller. The fan can then be started and will run at high speed in whichever direction the fan-run signal dictates: The control from OCC is generally performed using 'Mode Tables' for each system. This table defines the sequence of the desired equipments that need to be operated based on the event. The abnormal conditions such as train congestion, emergency, fire in subway would be detected by various components and the emergency response thereto will be activated based on the mode tables. In the event that remote control is not possible due to any reason, the local control via SCR would be performed. The OCC will also be used for logging the alarm status, fault occurrences, and other maintenance related data for the above systems. 12 COMPUTER SIMULATION The Subway Environmental Simulation (SES) Computer Program has been used to model the subway environment. The computer simulation program shall model the tunnel sections and all the stations. The simulation provides train performance and civil design data to aid in the design and verifies the adequacy of all systems during normal, congested and emergency conditions. The SES computer model provides a dynamic simulation of the operation of multiple bi-directional trains in a multi-track subway and permits continuous reading of the air velocity, temperature, and humidity throughout any arrangement of station, tunnels, ventilation shafts and fan shafts. The program is useful to simulate the fans of different capacities for the congestions and emergency considerations in the different tunnel sections of the corridor. In addition, the programme has been designed to provide readings of the maximum, minimum and average values for system air velocities, temperatures, and humidity during any preset time interval. The programme estimates the station cooling and heating capacities necessary to satisfy any given environmental criteria, as well as the percentage of time during which any specified environmental criteria are exceeded. Although a simulation can extend over any period of subway operations, the primary focus of the SES is on short-term simulations, such as the peak rush hours, when there is often an extreme deterioration of the subway environment. Both, the input information required by the programme and the output produced are tailored for the use of design engineers concerned with practical environmental problems. 13 CONCLUSIONS Thus a close type TVS has been adopted in DMRC. The system is so designed that it provides an acceptable environment in the tunnel and station track way for the operation of the trains during normal, Congested and emergency operations. The system design has already been successfully implemented in 13 underground stations, which have been completed in Phase-I. Now the similar system design criteria have been considered for 19 underground stations of phase II of DMRC. **** 193