Patent Publication Number: US-2023150675-A1

Title: Oxygen Pressure Relief and Ventilation System and Method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/280,685 entitled Oxygen Pressure Relief and Ventilation System And Method and filed on Nov. 18, 2021, the disclosure of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the invention relate generally to the field of aircraft supplemental oxygen systems, and more specifically to pressure relief and ventilation of aircraft supplemental oxygen systems. 
     2. Related Art 
     Safety mechanisms for emergency oxygen systems onboard aircraft are known. For example, U.S. Patent Application Publication No. 2019/0321660 to Klockiewicz et al. discloses an emergency oxygen system for an aircraft having a relief valve configured to vent pressure if a threshold is exceeded. U.S. Pat. No. 7,341,072 to Talty discloses a centralized flow control unit that regulates oxygen flow from an emergency oxygen distribution system in an aircraft. The flow control unit includes a flow control valve and a relief valve. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
     In an embodiment, an oxygen pressure relief and ventilation system includes: a flow fuse fluidly coupled downstream of a pressure regulator, wherein the pressure regulator is operatively coupled to an oxygen tank, and the oxygen tank is located in an unpressurized compartment of an aircraft; a pressure relief valve fluidly coupled downstream of the flow fuse; and a ventilation pathway fluidly coupling the unpressurized compartment with a pressurized compartment, wherein the flow fuse and the pressure relief valve are configured to cooperatively mitigate downstream flow of pressurized oxygen if the pressure regulator fails, and wherein the ventilation pathway is configured to allow air from the pressurized compartment to pass through to the unpressurized compartment for diluting a concentrated oxygen in the unpressurized compartment. 
     In another embodiment, a method for protecting against a failed pressure regulator of an oxygen system includes: partially blocking flow of a pressurized oxygen downstream of a failed pressure regulator via one or more flow fuses to isolate downstream components of the oxygen system from the pressurized oxygen; venting flow of the pressurized oxygen into an unpressurized compartment via one or more pressure relief valves to relieve pressure from the pressurized oxygen; and ventilating the unpressurized compartment with air from an occupied compartment via a pathway for diluting an oxygen concentration in the unpressurized compartment. 
     In yet another embodiment, a backup system for relieving oxygen pressure following failure of a pressure regulator includes: one or more flow fuses fluidly coupled downstream of one or more pressure regulators, respectively, wherein the one or more pressure regulators are operatively coupled to one or more oxygen tanks configured to supply oxygen to oxygen masks onboard an aircraft, and wherein the one or more flow fuses are configured to partially block a pressurized oxygen from flowing downstream to the one or more oxygen masks if the one or more pressure regulators fail; and a ventilation subsystem configured to fluidly couple an unpressurized compartment containing the oxygen tanks with a pressurized compartment, wherein the ventilation subsystem is configured to pass air from the pressurized compartment to the unpressurized compartment for diluting a high concentration of oxygen in the unpressurized compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG.  1    shows an embodiment of an aircraft configured with an oxygen pressure relief and ventilation system; 
         FIG.  2    is a diagram showing the oxygen pressure relief and ventilation system of some embodiments; 
         FIG.  3    shows a first portion of the oxygen pressure relief and ventilation system of  FIG.  2   , in some embodiments; 
         FIG.  4 A  shows a second portion of the oxygen pressure relief and ventilation system of  FIG.  2   , in some embodiments; 
         FIG.  4 B  shows the second portion of  FIG.  4 A  with a muffler installed, in some embodiments; and 
         FIG.  5    is a process-flow diagram illustrating an oxygen pressure relief and ventilation method using the system of  FIGS.  2 - 4   , in an embodiment. 
     
    
    
     The drawing figures do not limit the invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION 
     The following detailed description references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized, and changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the invention is defined only by the appended claims, along with the full scope of the equivalents to which such claims are entitled. 
     In this description, references to “one embodiment,” “an embodiment,” or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment,” “an embodiment,” or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     Aircraft that fly above certain altitudes (e.g., 10,000-feet above sea level or higher) typically require oxygen safety systems to provide 100% pure oxygen to crew and passengers via oxygen masks within the cabin and/or cockpit. The oxygen safety system includes one or more high-pressure gaseous oxygen tanks that store oxygen for the crew and passengers to access during the flight (e.g., when the aircraft cabin pressure altitude is above 10,000-feet). Such tanks may be stored with a nominal pressure of about 1,850 pounds per square inch (psi). At such a high pressure, releasing oxygen directly from the tank would damage downstream equipment, such as oxygen masks. Accordingly, the tanks are equipped with a pressure regulator, which reduces the pressure of the oxygen released from the tank to between about 60 psi to about 90 psi. The system relies heavily upon the stability and proper functioning of the single pressure regulator. Failure of the pressure regulator can lead to loss of the oxygen supply for the crew and passengers. Leakage from the oxygen system may lead to oxygen buildup within the compartment housing the oxygen supply system, which significantly increases the fire risk within the compartment. Furthermore, leakage that could occur upon failure of the regulator may also damage downstream components in the oxygen supply system. Therefore, safety systems are needed as a backup in case the pressure regulator fails. 
       FIG.  1    shows an aircraft  10  configured with an oxygen pressure relief and ventilation system. Aircraft  10  contains a cockpit  20  and a cabin  30 , which collectively represent the occupied compartment  40 . The occupied compartment  40  may be occupied by one or more of pilots, crew, passengers, or cargo. In embodiments, aircraft  10  is a pressurized aircraft such that occupied compartment  40  is pressurized. Pressurized aircraft are typically operated at altitudes above about 10,000-feet above sea level. At these altitudes, a pressurization system onboard the aircraft  10  maintains the pressure of the occupied compartment  40  at roughly the equivalent to the pressure at 10,000-feet or lower. Pressurized aircraft also, in some embodiments, include an oxygen supply system as a backup safety mechanism, for example, in the event that the pressurization system fails (i.e., the occupied compartment  40  pressure altitude exceeds 10,000-feet). The oxygen supply system may be located in an unpressurized zone, such as within an unpressurized compartment  50 , for safety reasons. Unpressurized compartments on aircraft may include the nose, tail, wings, or other spaces not occupied by passengers or crew. 
       FIG.  2    depicts an oxygen pressure relief and ventilation system  100 , in some embodiments. Oxygen system  102  may, in some embodiments, include an oxygen tank  104  and a pressure regulator  106 . In some embodiments, portions of oxygen system  102  (e.g., oxygen tank  104 , pressure regulator  106 , a flow fuse  112 , and a pressure relief valve  114 ) may be located in an unpressurized compartment, such as compartment  50 . In some embodiments, there may be one or more oxygen tanks  104  supplying oxygen to the crew and passenger oxygen masks  122 . In these embodiments, there may be one or more pressure regulators  106  corresponding to each of the one or more oxygen tanks  104 . For example, in some embodiments, there may be three oxygen tanks  104  and three pressure regulators  106 , such that each oxygen tank  104  is equipped with a pressure regulator  106 . In embodiments, the configuration of oxygen system  102  (e.g., size of oxygen tank  104 , number of oxygen tanks  104 , etc.) may be determined depending on one or more of the maximum number of crew and passengers, the cruising altitude of aircraft  10 , or the duration of the flight. 
     In some embodiments, the oxygen tank  104  and pressure regulator  106  may be fluidly coupled to a pressure relief system  110 , which in turn may be coupled to supply system  120 . In some embodiments, the pressure relief system  110  may be a subsystem of the aircraft oxygen system  102 . In some embodiments, the supply system  120  may be a subsystem of the oxygen system  102 . Portions of the pressure relief system  110  are further depicted in  FIG.  3   , and as such,  FIGS.  2  and  3    may be best viewed together with the following description. In some embodiments, pressure relief system  110  may include tubing  116 . Tubing  116  may be used to fluidly couple different components of oxygen system  102 . In some embodiments, tubing  116  may comprise a semi-rigid material. In some embodiments, tubing  116  may comprise one or more of a plastic or a rubber. In some embodiments, tubing  116  may comprise a substantially rigid material. In some embodiments, tubing  116  may comprise a hollow metal pipe. In some embodiments, tubing  116  may direct oxygen to the supply system  120 . 
     In embodiments, supply system  120  may include oxygen masks  122  and other critical components  126  of the oxygen system  102  that are located in occupied compartment  40 , as shown in  FIG.  2   . Portions of supply system  120  may be rated to withstand a specific amount of pressure (e.g., about 90 psi to about 135 psi). As such, pressures higher than this rating caused by, for instance, failure of pressure regulator  106 , may cause damage and/or failure of portions of supply system  120 . Below, embodiments will be discussed which may prevent damage of supply system  120  upon failure of pressure regulator  106 . 
     In embodiments, pressure relief system  110  may include flow fuse  112  (e.g., a flow fuse, an airflow fuse, or an air shutoff valve) and pressure relief valve  114  (see  FIGS.  2 - 3   ). In embodiments, the flow fuse  112  may be disposed downstream of the pressure regulator  106 . In some embodiments, the flow fuse  112  may be disposed upstream of the pressure relief valve  114 . In some embodiments, flow fuse  112  may comprise a pneumatically-actuated valve, such as a poppet valve. In some embodiments, flow fuse  112  may comprise a spring-loaded mechanism which biases the flow fuse  112  in a first position. In the first position, flow fuse  112  may allow pressurized oxygen from oxygen system  102  to reach supply system  120 . In some embodiments, flow fuse  112  may be configured to isolate pressurized oxygen of oxygen system  102  from downstream components (e.g., oxygen masks  122 ) upon a failure of pressure regulator  106 . For example, the flow of pressurized oxygen may exert a dynamic pressure force on the flow fuse  112 . If the flow of pressurized oxygen rises to a predetermined pressure, the resulting pressure overcomes the spring force and pushes the flow fuse  112  to a second position (e.g., against a seat). In embodiments, this may substantially block flow through the flow fuse  112 , thereby isolating high pressure oxygen flow from the downstream system components (e.g., supply system  120 ). For example, if pressure regulator  106  fails and pressurized oxygen is released at a pressure that surpasses the maximum normal 90 psi, the spring-loaded mechanism of flow fuse  112  may be triggered, therein biasing flow fuse  112  into the second position. In these embodiments, flow fuse  112  may substantially prevent high pressure surges of oxygen from oxygen system  102  from traveling to downstream systems, such as supply system  120 . In some embodiments, flow fuse  112  may comprise a mechanism configured for actuation to the second position upon exposure to a pressure of about 100 psi and above. In some embodiments, flow fuse  112  may automatically reset back to the first position when upstream pressure is restored below the maximum normal 90 psi. In some embodiments, pressure relief system  110  may comprise one or more flow fuses  112 . For example, if more than one oxygen tank  104  and pressure regulator  106  are used for oxygen system  102 , a plurality of flow fuses  112  may be used to direct pressurized oxygen flow from each oxygen tank  104  and pressure regulator  106 . In some embodiments, one flow fuse  112  may be used to direct air flow from multiple oxygen tanks  104 . For example, tubing may connect pressurized oxygen flow streams from two or more oxygen tanks  104  to a single flow stream via a manifold. In this case, a single flow fuse  112  may be placed downstream of the flow stream convergence (e.g., downstream of the manifold), thereby, in some embodiments, allowing a single flow fuse  112  to isolate pressurized oxygen flow from multiple oxygen tanks  104 . 
     In some embodiments, flow fuse  112 , when in the second position, may allow some pressurized oxygen to pass so as to not cause too high of a pressure in the tubing upstream of flow fuse  112 . In this case, pressure relief system  110  may include a pressure relief valve  114  located downstream of flow fuse  112 . Pressure relief valve  114  may, in embodiments, be configured to release pressurized oxygen upon exposure to a predetermined pressure, therein relieving oxygen system  102  of overburdening pressure. In embodiments, flow fuse  112  partially blocks high pressure oxygen (e.g., from sudden surges of high pressure) while pressure relief valve  114  releases excess pressure downstream of flow fuse  112 . 
     In some embodiments, pressure relief system  110  may comprise multiple pressure relief valves  114 . For example, in some embodiments there may be one pressure relief valve  114  downstream of every flow fuse  112 . In some embodiments, pressurized oxygen from multiple flow fuses  112  may feed into a single pressure relief valve  114 . For example, if multiple oxygen tanks  104  and pressure regulators  106  feed pressurized oxygen into multiple flow fuses  112 , these multiple sources of pressurized oxygen may converge into a single pressurized oxygen flow at a common manifold. Subsequently, this single pressurized oxygen flow may be fed into a single pressure relief valve  114 , therein the single relief valve  114  serves multiple pressurized oxygen sources. In some embodiments, pressure relief valve  114  may comprise a pneumatically-actuated valve, such as a poppet valve. In some embodiments, pressure relief valve  114  may comprise an internal poppet spring-loaded in the closed position, wherein internal static oxygen pressure pushes against the spring. In some embodiments, if the pressure becomes too high (i.e., above a threshold pressure), the force may overcome the spring force and open the pressure relief valve  114 . For example, pressure relief valve  114  may be configured to open upon exposure to a pressure of about 100 psi and above. Pressure relief valve  114 , in the open configuration, may be configured to release pressurized oxygen out of the oxygen system  102  into the ambient air. In some embodiments, pressure relief valve  114 , in the open configuration, may be configured to release pressurized oxygen out of the oxygen system  102  into the unpressurized compartment (e.g., compartment  50 ), forming a concentrated oxygen area therein. In these embodiments, sufficient venting of the concentrated oxygen in the unpressurized compartment may be needed to prevent oxygen build-up, and subsequent fire risk, within the compartment. This will be discussed further below with relation to other components of the oxygen pressure relief and ventilation system  100 , such as ventilation system  130 . 
     Within oxygen system  102 , there are several possible failure modes of the pressure regulator  106 . All failure modes may be classified into two categories: failures resulting in a small leak, and failures resulting in a large leak. If a failure resulting in a large leak occurs, flow fuse  112  may close as previously described to isolate the pressurized oxygen flow, therein preventing a surge of pressurized oxygen from reaching the supply system  120 . Any leakage through flow fuse  112  may cause the pressure supplied to supply system  120  to slowly increase. In embodiments, the pressure may continue to increase until one or more pressure relief valves  114  open due to the threshold pressure being reached. If a failure resulting in a small leak occurs, the flow fuse  112 , may, in embodiments, remain open due to the drag force resulting from the small amount of pressurized oxygen flow not allowing flow fuse  112  to close. In this case, the pressure supplied to the supply system  120  will slowly increase. The pressure may continue to increase until the one or more pressure relief valves  114  open to limit the increase in pressure. In this way, flow fuse  112  and pressure relief valve  114  function cooperatively together to protect against all possible failure modes of the pressure regulator  106 . 
     In some embodiments, oxygen pressure relief and ventilation system  100  may further include a ventilation system  130 . In some embodiments, ventilation system  130  may be a subsystem of oxygen pressure relief and ventilation system  100 . Ventilation system  130 , may, in some embodiments, dilute the concentrated oxygen in the compartment (e.g., compartment  50 ) when the concentrated oxygen resulted from the operation of the one or more pressure relief valves  114 , or other possible system leakages. In some embodiments, cabin pressurized air  124  from occupied compartment  40  (e.g., cockpit  20  and/or cabin  30 ) is used to ventilate the unpressurized compartment  50 . In some embodiments, ventilation system  130  comprises a fluid connection connecting one or more of the cockpit  20  and/or cabin  30  to the compartment  50 . While depicted in  FIG.  4 A  as connecting unpressurized compartment  50  and occupied compartment  40 , it is contemplated that any pressurized compartment may be connected to any unpressurized compartment to subsequently allow for ventilation of the unpressurized compartment. 
     In some embodiments, ventilation system  130  comprises a pathway configured to allow cabin pressurized air  124  to pass from the pressurized compartment (e.g., unoccupied compartment  40 ) to the unpressurized compartment (e.g., compartment  50 ). The pathway may comprise tubing that connects to an opening through a barrier, such a wall  150  between the pressurized and unpressurized compartments. Cabin pressurized air  124 , in some embodiments, provides a range of flow rates to substantially ventilate the unpressurized compartment while not interfering with the ability of the pressurization system to pressurize the cockpit  20  and cabin  30 . For example, if the flow rate of ventilation system  130  is too high, allowing too much air to flow freely from the pressurized compartment to the unpressurized compartment, then the pressurization system will not be able to compensate for the lost pressure and will therefore lose pressurization of the cockpit  20  and cabin  30 . Alternatively, if the flow rate of the ventilation system  130  is too low, not allowing enough air to flow from the pressurized compartment to the unpressurized compartment, then proper ventilation of the unpressurized compartment will not occur, therein not diluting the concentrated oxygen which originated, for example, from pressure relief valves  114 . Due to the aforementioned requirements of ventilation system  130 , in some embodiments, ventilation system  130  may comprise a regulated mechanism configured to allow a precise flow rate of cabin pressurized air  124  into the unpressurized compartment. 
     As depicted in  FIG.  4 A , in some embodiments, ventilation system  130  may comprise a tube  132 . Tube  132  is configured to allow a fixed flow rate of ventilation air (e.g., cabin pressurized air  124 ) to enter the unpressurized compartment, dependent upon the difference in pressure between the pressurized and unpressurized compartments. Tube  132 , in embodiments, includes a connection  134  between the unpressurized compartment  50  and the occupied compartment  40 . Connection  134  may comprise a hole through wall  150  between the compartments by which tube  132  may be secured. Tube  132  may further include inlet  136 . Inlet  136 , in some embodiments, may include internal mechanisms by which to adjust air flow therethrough. For example, inlet  136  may include a flow-limiting device such as a valve, wherein a specific amount of pressure allows ventilated air to flow through tube  132 . In some embodiments, inlet  136  may be configured to minimize noise penetration into the pressurized compartment. Tube  132  may further include a throat  138  disposed at an outlet of tube  132 . In some embodiments, throat  138  may be sized to allow the proper amount of ventilation air through tube  132 . In certain embodiments, throat  138  comprises a fixed venturi-style throat. 
     As depicted in  FIG.  4 B , ventilation system  130  may include a muffler  140  in some embodiments. Muffler  140  is configured for reducing noise produced by ventilation system  130 . For example, muffler  140  may comprise a hollow perforated tube wrapped in sound damping material and a flexible outer shell that encloses the sound damping material. Muffler  140  may be installed upstream of tube  132  in the occupied (i.e., pressurized) compartment  40  (as shown in  FIG.  4 B ), or muffler  140  may be installed in unpressurized compartment  50  (not shown) so long as the muffler  140  is installed upstream of throat  138 . Tubing  142  is used to fluidly connect tube  132  with muffler  140 . 
     In some embodiments, unpressurized compartment  50  may include a vent (not shown) that allows air to exit from the unpressurized compartment  50  into the ambient environment. Such a vent may prevent unpressurized compartment  50  from becoming pressurized. Furthermore, such a vent may allow for proper ventilation of the unpressurized compartment  50  if a concentrated oxygen environment occurs. 
     The benefits of ventilation system  130  providing ventilated air from a pressurized compartment rather than ambient air from outside aircraft  10  are three-fold. First, the use of ventilated air avoids introducing additional moisture or other contaminants into the unpressurized compartment that may be present in the ambient air. Second, ventilated air from the pressurized compartment is typically controlled to room temperature. Therefore, fluctuations of the air temperature within the unpressurized compartment are less extreme than they may be when ventilating with ambient air. This may increase reliability of, for example, electronic components which may be present in the unpressurized compartment  50 . Third, ventilation from internally provided ventilated air prevents aerodynamic drag of the aircraft  10  which may otherwise be exerted due to ventilation with external ambient air. 
     Overall, oxygen pressure relief and ventilation system  100 , in embodiments, may mitigate and prevent damages caused by a failure of the pressure regulator  106  in three separate ways. First, flow fuse  112  may isolate pressurized oxygen upon an increase in pressure, thereby preventing it from reaching and damaging downstream components, such as oxygen masks  122 . Second, pressure relief valve  114  may release pressure from the oxygen system  102 , further mitigating the increase in pressure on the oxygen system  102  due to a failure of the pressure regulator  106 . Third, a significant increase in oxygen levels in the unpressurized compartment  50  via concentrated oxygen is prevented by ventilation system  130  by providing a sufficient amount of ventilated air to dilute the concentrated oxygen, therein mitigating the risks of a fire onboard due to significantly high oxygen concentrations. 
     Turning now to  FIG.  5   , a process flow diagram is depicted illustrating an exemplary oxygen pressure relief and ventilation method  200 , performed using, for example, the oxygen pressure relief and ventilation system  130  of  FIGS.  2 ,  4 A and  4 B . 
     In a step  202 , the oxygen pressure relief and ventilation method  200  starts. 
     In a step  204 , the pressurized oxygen flow is isolated. In an example of step  204 , a flow fuse (e.g., flow fuse  112 ) may be used to isolate pressurized oxygen if a threshold pressure is reached. For example, if a pressure regulator (e.g., pressure regulator  106 ) fails, and a significant increase in pressurized oxygen is received by the system (e.g., oxygen system  102 ), the downstream components, such as oxygen masks  122 , may need to be protected from a surge in pressure. As such, the pressurized oxygen is isolated from the downstream components via the flow fuse, thereby preventing the downstream components from being damaged. 
     In a step  206 , the pressurized oxygen flow is relieved. In an example of step  206 , pressure relief valves (e.g., pressure relief valve  114 ) open in response to an increase in pressure caused by, for instance, a failed pressure regulator (e.g., pressure regulator  106 ). In this step, one or more pressure relief valves may operate to relieve pressure from the system (e.g., oxygen system  102 ) by releasing pressurized oxygen. The one or more pressure relief valves may be located downstream of the flow fuse such that the flow fuse and pressure relief valve(s) function together to protect against all possible failure modes of a pressure regulator, as described above. In embodiments, the pressurized oxygen is released into an unpressurized compartment such as compartment  50 . 
     In a step  208 , concentrated oxygen is ventilated. In an example of step  208 , compartment  50  is ventilated using an internal ventilation system (e.g., ventilation system  130 ). In another example, a ventilation system may release ventilated air from a pressurized compartment (e.g., cockpit  20  or cabin  30 ) into the unpressurized compartment  50  to dilute the concentrated oxygen within the unpressurized compartment  50 . In some embodiments, the unpressurized compartment  50  may include a vent that allows air to exit from the unpressurized compartment into the ambient environment. The concentrated oxygen may result from a leak of the oxygen system  102  or from release of pressurized oxygen via pressure relief valve  114 , for example. Such a ventilation system may reduce fire risk within the unpressurized compartment by reducing the oxygen concentration. 
     Oxygen pressure relief and ventilation method  200  vastly improves the efficacy and safety of onboard oxygen supply systems. Currently, minimal or no safety mechanisms exist for many aircraft to respond to a failed pressure regulator. As such, there is a significant need for protection systems and methods to prevent damage to critical air supply components onboard the aircraft as well as significant fire risk due to a large increase in oxygen concentrations within a compartment of the aircraft. 
     Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims. 
     Having thus described various embodiments of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: