Patent Publication Number: US-2022211230-A1

Title: Ventilation and Particulate Matter Removal System

Description:
FIELD 
     Apparatus systems and methods are disclosed for removal of particulate matter from enclosed spaces and enclosures, with particular reference to removal of dust, dirt and the like from enclosed cabinets containing electrical components. 
     BACKGROUND 
     In many industries, electrical, electronic and other sensitive equipment is housed in enclosures designed to provide a safe and clean operating environment for that equipment and to prevent unauthorized or inadvertent access. This can be the case in both fixed industrial installations and mobile equipment. 
     Although such enclosures are generally designed and maintained to prevent or limit ingress of particulate matter, for example dust and dirt, it has been found in some applications that enclosures do sometimes need to be cleaned out of such particulate matter. Failure to do so in these applications can eventually threaten proper operation of the electrical or electronic equipment. 
     For example, in the mining industry, haul trucks with diesel-electric drives have enclosures (cabinets) for electrical components which are sometimes found to accumulate significant quantities of particulate matter, even when carefully maintained, but particularly with ageing and when maintenance is imperfect. Other mobile equipment used in the surface mining industry, eg electric blasthole drills, shovels and draglines may have enclosures that are similarly affected. 
     Cleaning out of particulate matter from such enclosures to a suitable standard of cleanliness can itself be difficult and time consuming. Water cleaning is unsuitable for cleaning electrical and electronic equipment. Vacuum cleaning is often ineffective in removing particulate matter from spaces within and between components. The use of compressed air can create occupational, environmental and ecological exposure risks from airborne particulate matter. 
     It is believed that there are other areas of activity including for example underground mining, and certain above-ground industrial/manufacturing installations in which the above problems occur. In some of these, the particulate matter in question may be considered toxic either inherently because of its chemistry or because of factors such as particle size or shape or even the expected sensitivity of persons likely to be exposed to the matter. 
     Disclosed herein are equipment, systems and methods for addressing the problem of cleaning particulate matter from enclosed spaces. 
     In this specification, no reference to prior art or to what is known, is to be taken as a concession that anything is a part of the common general knowledge in Australia or elsewhere. 
     DISCLOSURE OF THE INVENTION 
     The invention provides in a first aspect a cleaning and ventilation system. 
     More particularly there is provided apparatus for removing particulate matter from an enclosure having an internal space and an opening into the internal space, comprising: 
     a cover positionable adjacent the opening so that the cover covers the opening; 
     a gas source external to the internal space; 
     an inlet conduit that in use extends through the cover and is adapted to direct gas from the gas source to at least one gas outlet within the internal space whereby particulate matter within the internal space is dislodged and entrained in gas within the internal space; 
     a source of partial vacuum adapted to maintain a partial vacuum within the internal space and to draw gas and particulate matter entrained therein from the internal space firstly through an outlet conduit and then through a particulate matter separation means comprising at least one filter; 
     a sensor for sensing concentration of particulate matter in gas leaving the enclosed space; 
     a display adapted to provide to a user information on concentration of particulate matter leaving the internal space so that the operator can continue use of gas from the gas source to dislodge particulate matter in the internal space until a satisfactory value of the concentration is achieved. 
     Preferably the apparatus further comprises means for storing data obtained from the sensor. 
     Preferably also, the apparatus further comprises means for transmitting data obtained from the sensor to a location remote from the apparatus. 
     The outlet conduit is preferably in use secured to the cover and draws gas through an opening in the cover. 
     Preferably the or at least one gas outlet is movable relative to the cover among multiple positions within the internal space. 
     In a preferred embodiment the gas outlet is at an end of an elongate lance comprised in the inlet conduit, the lance in use extending though a port in the cover so that a portion of its length is in the internal space and the user can manually move the lance to cause the gas outlet to take up any of the said multiple positions within the internal space. 
     It is particularly preferred that the elongate lance comprises a display adapted to display data sensed by the sensor. 
     Gas flow to the gas outlet may be able to be interrupted periodically so that the flow of gas leaving the elongate lance within the internal space pulsates. 
     The port in the cover may be one of a plurality of ports in the cover so positioned that the user can withdraw the lance from one port and enter the lance into another port as required to access multiple parts of the internal space. 
     Desirably, each of the plurality of ports is adapted to prevent or limit escape of particulates therethrough when the port does not have the lance extending through it. 
     The cover may comprise a sheet of flexible transparent material so that a user may see through the cover when using the elongate lance. 
     The invention further provides a method for removing particulate matter from an enclosure having an internal space and an opening into the internal space, comprising the steps of: 
     positioning a cover adjacent the opening so that the cover covers the opening; 
     providing a gas source external to the internal space; 
     providing an inlet conduit that in use extends through the cover and is adapted to direct gas from the gas source to at least one gas outlet within the internal space whereby particulate matter within the internal space is dislodged and entrained in gas within the internal space; 
     providing a source of partial vacuum adapted to maintain a partial vacuum within the enclosed space and to draw gas and particulate matter entrained therein from the internal space firstly through an outlet conduit and then through a particulate matter separation means comprising at least one filter; 
     providing a sensor for sensing concentration of particulate matter in gas leaving the enclosed space; 
     using the sensor to derive and provide to a user information on concentration of particulate matter leaving the internal space; 
     the user using gas from the gas source to dislodge particulate matter in the internal space until a satisfactory value of the concentration is achieved. 
     The method may further comprise the steps of: 
     repeatedly sensing concentration of particulate matter in gas leaving the internal space during cleaning thereof and storing digital records thereof. 
     The method may include the step of transmitting the digital records to a remote location. This enable analysis at the remote location, which may be done for validation that cleaning is satisfactory and for regulatory approval purposes. 
     The method therefore may include the step of receiving transmitted the digital records and analysing the effectiveness of cleaning on the basis of the digital records. 
     There is also provided a system for instrumentation and control of a mechanical ventilation system where both equipment-related sensors and workspace- and/or user-related sensors are provided, and wherein signals from specific ones of the sensors (workplace-, user-, or equipment-related) are used to provide any or all of alarms (or warnings), display the parameter value(s) of concern and if desired or necessary shut down or otherwise control either the ventilation system or the equipment being ventilated. 
     Some industrial processes require different levels of ventilation according to how a the process is being carried out or the stage it has reached, and it is desirable to be able to adjust ventilation to suit—either to provide adequate ventilation or to limit wastage of energy when a particular level of ventilation is not required. Therefore, instead of, or in addition to, alarms, warnings and shutdown commands, the system may provide for automatic control of the ventilation system to maintain effectiveness and save energy in a range of conditions. 
     The systems and embodiments described above amount to examples of the further inventive concept introduced in the previous paragraph. Further examples of potential application areas include grinding equipment and saws (eg for cutting stone kitchen benchtops, a known area of particulate problems). Both mobile and fixed types of equipment can provide other potential applications. 
     Further embodiments and additional features and inventive concepts are described in the following detailed description, based on the attached drawings. 
     Everywhere in this specification, the word “comprise” and derivatives thereof including “comprising”, “comprised” and the like, when used in relation to items, elements or steps, are to be taken as indicating presence of those items elements or steps, but not as precluding the possible presence of other items, elements or steps. 
     Everywhere in this specification, the terms “particulate” and “particulates” are to be understood as short and convenient terms for particulate matter. It is further to be understood that the particulate matter described will in some applications comprise particles with a range of sizes. Except where otherwise stated, the terms “sealingly” and “gas-sealingly”, where used in this specification in relation to two parts or elements, are to be taken to mean that gas and particulate matter entrained in that gas are wholly or substantially or at least to a useful degree prevented from leaking or passing between the two parts or elements. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIG. 1( b )  is a perspective view of an enclosure being cleaned; 
         FIG. 1( a )  is a cross-sectional view of the enclosure shown in  FIG. 1( b )  being cleaned; 
         FIG. 2  is a schematic diagram showing components of a cleaning system according to an aspect of the invention and connections between those components; 
         FIG. 3  is a block diagram of instrumentation and control components; 
         FIG. 4  is a perspective view of a cabinet for electrical components partially modified to implement the invention; 
         FIG. 5  is a partial exploded perspective view of the cabinet shown in  FIG. 4 ; 
         FIG. 6  is a perspective partially exploded view of an assembly comprising a frame and door of the cabinet shown in  FIG. 4 ; 
         FIG. 7  is a front elevation of the cabinet shown in  FIG. 4 ; 
         FIG. 8  is a partial section of the cabinet of  FIG. 7 , the section being taken at station BB in  FIG. 7 ; 
         FIG. 9  is an enlarged view of detail A of  FIG. 8 ; 
         FIG. 10  is a sectional view of the cabinet as shown in  FIG. 7 , the section being taken at station DD of  FIG. 6 ; 
         FIG. 11  is a vertical section through an alternative port assembly according to the invention, when in use; 
         FIG. 12  is a vertical section equivalent to  FIG. 11  showing the alternative port assembly of  FIG. 11 , now when not in use. 
         FIG. 13  is a view exactly equivalent to  FIG. 8  of a temporary version of the frame shown in  FIG. 8 ; 
         FIG. 14  is a vertical section view of an enclosure fitted with a temporary cover according to an embodiment of the invention; 
         FIG. 15  is a side view of a cleaning lance according to the invention fitted with a collar assembly; 
         FIG. 16  is a perspective view of a cabinet and a further cover assembly positioned ready to be secured to the cabinet; 
         FIG. 17  is an elevation of a clamp assembly as shown in  FIG. 16  and as seen looking in the direction of arrow “17”; 
         FIG. 18  is a cross-sectional view of a port assembly of the cover shown in  FIG. 16 ; 
         FIG. 19  is a perspective view of the port assembly shown in  FIG. 18 ; 
         FIG. 20  is a sectional view of an enclosure showing a method of blowing gas according to the invention that is an alternative to that of  FIG. 1( a ) ; 
         FIG. 21  is a sectional view of an enclosure showing an method of blowing gas according to the invention that is an alternative to that of  FIG. 1( a ) ; 
         FIG. 22  is a side view of an open-topped railcar (whose upper section is shown in longitudinal cross-section) and a cleaning apparatus according to a further aspect of the invention; 
         FIG. 23  is a side view, with one portion shown in section, of an assembly of components of the system shown in  FIG. 2 ; 
         FIG. 24  is a perspective view of a cabinet and a further cover assembly positioned ready to be secured to the cabinet; 
         FIG. 25  is a longitudinal central section of a shipping container (with some detail omitted) fitted with particulate removing equipment; 
         FIG. 26  is a longitudinal central section (equivalent to  FIG. 25 ) of a shipping container (with some detail omitted) fitted with alternative particulate removing equipment; 
         FIG. 27  is a longitudinal central section of a barrel-type container fitted with apparatus for removing particulate matter; 
         FIG. 28  is a set of three schematic diagrams showing different ways in which the apparatus and methods described herein may be applied; 
         FIG. 29  is an elevation of an exterior side of a further enclosure cover according to the invention; 
         FIG. 30  is a partial cross-section taken at station “ 30 - 30 ” in  FIG. 29 ; 
         FIG. 31  is a partial cross-section taken at station “ 31 - 31 ” in  FIG. 29 ; 
         FIG. 32  is a schematic view of an enclosure of components of the invention and an enclosure being cleaned, these two enclosures being connected by a duct through which gas and particulate matter is withdrawn from the enclosure being cleaned. The duct is shown in section; 
         FIG. 33  is a perspective view of yet another cover assembly according to the invention; 
         FIG. 34  is an elevation of a portion of a prototype system according to the invention; 
         FIG. 35  is an exploded view of the prototype portion shown in  FIG. 34 , now with a filter holder and screw cap removed as if for emptying of filter bag; 
         FIG. 36  is a perspective view of an elongate filter bag holder for use in the invention; 
         FIG. 37  is a transverse sectional view of the holder of  FIG. 36  in use with a contained filter bag, the section being taken at station “A” of  FIG. 36 ; 
         FIG. 38  is a perspective view of still another cover assembly according to the invention, shown in a vertical orientation; 
         FIG. 39  is a perspective schematic view of a light source for use in the cover assembly of  FIG. 38 ; 
         FIG. 40  is a cross sectional view on a vertical plane through one port of the cover assembly shown in  FIG. 38 ; 
         FIG. 41  is a schematic block diagram of an instrumentation, data processing and communication system of an embodiment; 
         FIG. 42  is a perspective view of a further cover assembly and an enclosure, the cover assembly being shown positioned for placement on an opening of the enclosure; 
         FIG. 43  is a partial cross-section of the cover assembly of  FIG. 42 , the section taken at station “AX-AX”; 
         FIG. 44  is a perspective view of an exterior portion of the cover assembly shown in  FIG. 42 ; 
         FIG. 45  is a perspective view of a still further cover assembly and an enclosure, the cover assembly being shown positioned for placement on an opening of the enclosure; 
         FIG. 46  is a side elevation of a cleaning lance according to the invention; 
         FIG. 47  is a perspective view of a portion of the cleaning lance as shown in  FIG. 46 ; 
         FIG. 48  is a schematic diagram showing components of a further cleaning system according to the invention; 
         FIG. 49  is a schematic elevation of a motor-generator set; 
         FIG. 50  is a schematic elevation of the motor generator set of  FIG. 49 , now showing by dotted lines spaces in which the invention may be applied; 
         FIG. 51  is a side elevation of a portion of the motor generator set as shown in  FIG. 49 ; 
         FIG. 52  is aside elevation the same as  FIG. 52 , save for the addition of a cover assembly according to the invention; 
         FIG. 53  is a cross-section taken at station “Q-Q” of  FIG. 52 ; 
         FIG. 54  is a cross-sectional view of a cover assembly portion, the section being taken at station “R-R” of  FIG. 52 ; 
         FIG. 55  is a perspective view of an end portion of the motor generator set of  FIG. 49 , now fitted with cover assemblies according to the invention; 
         FIG. 56  is a schematic view of an arrangement in which a dust hood is ventilated and may be cleaned according to the invention; 
         FIG. 57  is a view of a particulate cleaning and ventilation system according to the invention comprising the system as shown in  FIG. 34  in combination with a pre-treatment system; 
         FIG. 58  is a schematic of the pre-treatment system as shown in  FIG. 57 ; 
         FIG. 59  is a partial view of a modified version of the system as shown in  FIG. 34 , in use and with a portion of its ductwork shown in section; 
         FIG. 60  is the same view as in  FIG. 59  of the system shown in  FIG. 59  in use and with a portion of its ductwork shown in section; 
         FIG. 61  is a perspective view of a further cleaning lance according to the invention; 
         FIG. 62  is a perspective view of a duct connection assembly for use with a flexible cover assembly, secured to a structure; 
         FIG. 63  is a schematic view of an enclosure being cleaned in accordance with an aspect of the invention; 
         FIG. 64  is a schematic view of an enclosure being cleaned in accordance with an additional aspect of the invention; 
         FIG. 65  is a perspective exploded view of a yet further cover assembly according to the invention; 
         FIG. 66  is a horizontal cross-section of the cover assembly as shown in  FIG. 65  in position for placement over an opening of a cabinet, the section being taken at the position of arrow “Z” in  FIG. 65 ; 
         FIG. 67  is a partial horizontal cross-section of the cover assembly as shown in  FIG. 65 , the section being taken at the position of arrow “Z” in  FIG. 65 ; 
         FIG. 68  is a partial horizontal cross-section of a modified form of the cover assembly as shown in  FIG. 65 , the section being taken at the position of arrow “Z” in  FIG. 65 ; 
         FIG. 69  is a partial horizontal cross-section of a further modified form of the cover assembly as shown in  FIG. 65 , the section being taken at the position of arrow “Z” in  FIG. 65 ; 
         FIG. 70  is a partial horizontal cross-section of a yet further modified form of the cover assembly as shown in  FIG. 65 , the section being taken at the position of arrow “Z” in  FIG. 65 ; 
         FIG. 71  is a perspective view of a yet further cleaning lance according to the invention; 
         FIG. 72 , is a further perspective view of the cleaning lance shown in  FIG. 71 ; 
         FIG. 73  is a perspective view of a cleaning lance portion according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following description, based on  FIGS. 1-3 , is based for convenience on arrangements and methods for cleaning particulates from cabinets such as those used for containment of electrical and electronic components and the like. However, other arrangements and applications are disclosed also, and it is to be understood that the same principles are applicable to them. 
       FIGS. 1 ( a ) and 1( b )  show schematically how an internal space  2  of a cabinet (that is, an enclosure)  4  containing electrical (or other) components  6  can have accumulations of particulates removed. 
     A door  8  of cabinet  4  seals against fixed part  5  of cabinet  4  due to a seal  7  that extends peripherally around the edge of door  8 . Door  8  has at least one port assembly  10  through which a rigid, elongate cleaning lance  12  can be inserted so that a part of its length is in internal space  2 . Cleaning lance  12  is elongate and tubular and provided with gas from a source  32  (see  FIG. 2 ) external to cabinet  4 , the gas being expelled in a stream or jet from a nozzle  14 , nozzle  14  being inside internal space  2  during that part of the cleaning process shown in  FIG. 1( a ) . In some embodiments, cleaning lance  12  has a manually operable valve  16  for control (including shutoff) of gas flow through nozzle  14 . Blowing a stream or jet of gas into internal space  2 , as shown in  FIG. 1( a ) , allows dislodgement of particulates from internal surfaces of cabinet  4  and components  6  and agitation of dislodged particulates so that they are entrained in gas within the internal space  2 . Cleaning lance  12  can be manipulated by a user outside enclosure  4  so as to move the stream of gas ejected from it inside enclosure  4 . 
     Cabinet  4  also has at least one outlet port  18  through which gas and entrained particulates can leave internal space  2  and be drawn into a duct  20  by an external source (see item  46 ,  FIG. 2 ) of at least partial vacuum. As will be described further below, at least some of the particulates removed through outlet port  18  are removed from the gas downstream of outlet port  18 . Outlet port  18  is shown as comprised in door  8 , but may in alternative embodiments (not shown) be comprised in fixed part  5  of cabinet  4 . The position of the outlet port is selected to benefit from gravitational settling and stratification of the dust so that the dust can be extracted as completely as possible. Further, an extension duct (not shown) may be fitted to the outlet port  18  to move the location from which gas and entrained particulates further into the enclosure  4 . (This approach may also be taken in other embodiments described below.) 
     Cleaning lance  12  can be manually oriented (as shown by arrows  15 ), and the extent of its penetration into space  2  varied (as shown by arrows  17 ), by a user of cleaning lance  12  to orient and position nozzle  14  to best effect for dislodging particulates. Door  8  is provided with a transparent viewing window  22  so that the cleaning lance  12  in internal space  2  can be seen during cleaning. The purpose of providing multiple ports  10  is to enable a user to withdraw cleaning lance  12  from one port  10  and then insert it into another port  10  so as to dislodge particulates in multiple locations in internal space  2 . 
     Cleaning lance  12  is a gas discharging device and essentially comprises a gas flow control valve  16  for manual operation by a user and an elongate tube  13  through which gas leaving valve  16  passes to nozzle  14  from which it issues in a gas stream or jet. Nozzle  14  may be of any suitable form or may be omitted altogether so that gas simply issues from an open end of tube  13 . Nozzle  14  may direct gas at an angle to the length of tube  13 , for example, or may even be freely rotatable about a lengthwise axis of tube  13  and expel gas at an angle to tube  13  such that reaction force from the gas stream causes the nozzle  14  and its emerging jet of gas to rotate. Nozzle  14  may optionally simply comprise an open end of tube  13 , but in other embodiments would comprise a fixture that causes gas to increase in speed (hence momentum) as it leaves tube  13 . Such a nozzle  14  may be detachable from tube  13 . 
     In use of the method and apparatus illustrated in  FIG. 1( a ) , particulate dislodgement and removal from the internal space  2  is continued until there is a satisfactorily low concentration of particulate matter entrained in the gas leaving the internal space  2 . As set out below, a sensor for such concentration is provided, and information on the concentration is provided to a user so that cleaning can cease when the concentration is low enough. By maintaining a pressure in the internal space  2  that is lower than the atmosphere outside the internal space  2 , leakage of particulate around the door  8  or through the ports  10  during the cleaning operation is limited or prevented. Concentration measurement provides an objective criterion for ending the cleaning process. 
       FIG. 1( b )  shows another mode for particulate removal from internal space  2 . Door  8  has been opened and particulates are being drawn into a duct  24  by the above (or a second) partial vacuum source. Particulate removal in this way may be done before or after a period of particulate blowing as shown in  FIG. 1( a )  as found appropriate or between periods of particulate blowing. 
     In some applications, it is appropriate to remove significant accumulations of particulates first by the method shown in  FIG. 1( a )  and then through use of the conventional vacuuming approach of  FIG. 1( b ) . 
     While the methods of  FIGS. 1( a ) and 1( b )  have been illustrated by reference to an enclosure  4  with modifications to its door  8 , there will be described below embodiments in which a temporary cover is placed over an opening of an enclosure having an internal space instead of a door. 
     Although  FIG. 1( a )  shows all port assemblies  10  to be provided in door  8 , it is possible to provide port assemblies (not shown) in other parts (eg top, bottom or side walls) of cabinet  4 . 
     The gas may be air in suitable cases or may be an inert gas such as (for example only) nitrogen or carbon dioxide (derived for example from dry ice). Inert gas may be appropriate where fire, explosion or chemical reaction is a potential hazard. 
       FIGS. 2 and 3  show schematically an embodiment of a cleaning system  30  that is operable as described above to remove particulates from the enclosure  4 . System  30  includes an instrumentation and control system  199  that is not shown in  FIG. 2 , but whose functionality is illustrated separately and schematically in  FIG. 3 . 
     Referring firstly to  FIG. 2 , a gas source  32  is provided to direct gas to nozzle  14  through a conduit  34  which includes both a flexible hose portion  33  and cleaning lance  12 . Where air is to be the gas, gas source  32  may comprise, for example, a pump or blower (centrifugal or axial or a hybrid of these) or a reciprocating-piston compressor or a container of compressed air. In some applications and facilities, a reticulated compressed air supply (not shown) may be available and a connection thereto can constitute gas source  32 . Gases other than air may be used, being stored as a gas, or as a liquid or solid that changes phase on or before discharge, or generated by chemical reaction. 
     Conduit  34  may comprise flexible hose to enable manipulation of the cleaning lance  12 . 
     Item  52  in  FIG. 2  represents one or more components for conditioning and controlling the gas supply to lance  12 . It is preferred that the gas supply is conditioned to be substantially oil- and moisture-free, and components are known in the art for achieving this. More will be said about item  52  below. 
     Gas and entrained particulates are drawn out of enclosure  4  through duct  20  connected to enclosure  4  at outlet port  18  and then through a cyclone separator  38  (of which one is shown, but multiple cyclones may be used if appropriate to a particular application) and filters  40  and  42  by a blower  46 . Together the cyclone  38  and filters  40  and  42  remove particulate matter to a desired standard (particle size and concentration). One or more of the filters  40 ,  42  may be a “High Efficiency Particulate Air” (HEPA) filter. Although two filters  40  and  42  are shown in  FIG. 2 , this is not intended to be a limitation. More than two filters may be used, or in suitable cases even one filter only or no filter at all. Duct  20  may comprise a length of suitable flexible ducting. Where duct  20  comprises a flexible material reinforced with a spiral wire, or otherwise comprises conductive material along its length, that wire or conductive material may be preferably earthed to limit explosion risk when battery power is used for the system  30 . 
     To draw gas and entrained particulates from the enclosure  4 , a vacuum source, such as a suitable fan or blower  46  is provided so that pressure in duct  20  is reduced. As shown in  FIG. 2 , this may be located downstream of the cyclone  38  and filters  40  and  42 . 
     To also enable direct vacuuming of particulates from enclosure  4  as shown in  FIG. 1( b ) , duct  20  may be disconnected from outlet port  18  and used as vacuum hose  24 . Alternatively, as shown in  FIG. 2 , a separate duct  48  may be provided that is connected to duct  20  via a selector valve  50  and used as duct  24 . Selector valve  50  allows selection of direct vacuuming through duct  48  (as in  FIG. 1( b )  or removal of gas and entrained particulates as in  FIG. 1( a ) . Duct  48  is shown with an end fitting  47  for increasing the flow velocity of flow into duct  48 . Such a fitting may also be used (not shown) with duct  20  if duct  20  is used as duct  24  for direct vacuuming. 
     Selector valve  50 , where provided, may be adapted to ensure that some suction is maintained in duct  20  even when duct  48  is in use. 
     In some embodiments, end fitting  47  may be of the same or similar form as lance  12 , so as to be enterable into any of ports  10  and enable direct vacuuming of particulates with door  8  closed. In still further embodiments lance  12  itself is provided with an inlet for gas from the gas source  32 , as above, and additionally with a connection for duct  48 , allowing either suctioning via duct  48  or blowing with gas from gas source  32 . In such embodiments valve  16  comprises a selector for enabling sucking or blowing. 
     Still another alternative to the arrangement mentioned in the previous paragraph is to use a separate vacuum cleaner (not shown) for direct vacuuming in cabinet  4 . 
     Depending on the intended capacity of the system  30 , some or all of the components shown to the left of station “XX” in  FIG. 2 , including relevant parts of instrumentation and control system  199  may be provided in a single enclosure. This may be a fixed installation (not shown), or wheel or skid-mounted (not shown), or even comprised in a backpack-type enclosure. In some embodiments, as stated above, gas supply  32  is simply a connection to a reticulated compressed air supply. 
     It has been confirmed by applicants that a version of system  30  adequate for use in cleaning particulates from electrical cabinets of large diesel-electric mining haul trucks can be implemented in an enclosure the size of a small-to-medium suitcase. 
     Instrumentation and Control 
     Instrumentation and control system  199  will now be described, still using the electrical cabinet cleaning application shown in  FIG. 1  for illustrative purposes. (Some other applications mentioned below may not require all the functionality described.) Locations in the system  30  which may be provided with sensors of various types are labelled A to L in  FIG. 2 . 
       FIG. 3  is not intended as a detailed indication of hardware components and their connections. It is intended to explain what the system  199  does. The functions are straightforward enough for persons of ordinary skill in the art to implement without more specific detail. 
     Sensors and associated signal conditioning may be provided in system  30  for the following purposes:
         (a) to ensure that when particulates are being removed by entrainment, as in  FIG. 1( a ) , it is able to be known when a satisfactorily low concentration of particulates is entrained in gas being drawn from the enclosure being cleaned (eg cabinet  4 ), (whichever one of port assemblies  10  is in use) so that that process is complete;   (b) to enable monitoring of gas leaving blower  46  to ensure it has a satisfactorily low concentration of entrained particulates, so that persons near the point of discharge of gas leaving blower  46  are protected from harm;   (c) to enable monitoring of the operation of the various particulate-separation components of the system  30  and so ensure that filters  40  and  42  and cyclone  38  (in particular) are cleaned or emptied when appropriate and blower  46  cleaned if necessary;   (d) to ensure that components  6  in the enclosure being cleaned (eg  4 ,  60 ) and blower  46  are not exposed to unsafe/damaging temperature levels;   (e) to enable monitoring of pressure in the enclosure  4  being cleaned to ensure it remains in a range where there is neither damage to the enclosure  4  nor leakage of particulates from the enclosure  4 , in particular by maintaining pressure in the enclosure below atmospheric pressure in the surroundings where work is being carried out;   (f) to enable monitoring of the position and/or functioning of the seal  7  and door  8 ; and   (g) to provide necessary inputs for automatic control of parts of the system  30 ;   (h) to enable remote (or local) monitoring of the condition of the various parts of the system, so that maintenance and servicing can be carried out in a timely fashion.       

     Depending on requirements of particular applications and users, embodiments may comprise sensors for all or some only of these purposes. Outputs from the sensors can be used in some or all of the following several ways, as follows: 
     First, sensor outputs may be displayed directly as numerical measures—for example, pressure or blower  46  temperature in the enclosure being cleaned may be displayed on a suitable display. Alternatively, they can be displayed as “OK/Not OK” visual signals—for example it may be sufficient to indicate that a connected gas supply has pressure enough to be used rather than display its actual value. 
     Second, numerical quantities may be computed from sensor outputs and displayed—for example flow rate of gas through fan  46  or cleaning lance  12 . Derived quantities also may be provided only as “OK/Not OK” visual indications. 
     Third, audible or visible alarms can be generated where necessary and diagnostic messages displayed to guide correction by users. Further, alarm conditions may be used to trigger an automatic shutdown or otherwise limit operation of the system, i.e. to provide a “fail-safe” capability. 
     Fourth, sensor outputs and quantities derived from them may be recorded by a data logging facility, for verification or diagnostic purposes. For data logging, time stamping of data may be provided and even location may be recorded by provision of a GPS module. This use of sensor outputs is particularly important where it is desired not only to clean enclosures but to ensure that there is proof and/or certification of the standard of cleaning that has been carried out. This is potentially vital in applications where diseases such as silicosis, “black lung” disease and diseases associated with asbestos are to be avoided, for example. Further, purpose (h) above becomes very important in applications where logged data is to be provided to an off-site organisation for monitoring/certification purposes. Only if the equipment&#39;s condition can be maintained properly can results be relied upon. 
     Fifth, as well as the fail-safe capability mentioned above, automatic control of parameters and components may be provided using sensor outputs, as discussed below. 
     Particular choices from the above can be made according to intended applications. 
     Regarding purposes (a) and (b) above, the extent of particulate concentration in gas flows can be sensed using triboelectric particulate sensors. These are available from suppliers such as Auburn Filtersense LLC of Beverly, Mass., USA. While triboelectric-type sensors are suitable, other types are known in the instrumentation art and can be used as appropriate, for example sensors based on interruption or attenuation or transformation of a beam or beams of infra-red radiation, visible light, laser, beta rays or other EMF or nuclear radiation by particulates, or even acoustic-type sensors (in effect microphones) which react to impacts of particulates on a surface. The appropriate choice will depend on the particular application at hand. 
     Thus, to achieve aim (a) above, there may be provided one or more triboelectric (or other suitable) sensor(s) at station F (or a position upstream of it, or even inside space  2 ), 
     Operation of triboelectric sensors are sensitive to electric charge due to contact between dust particles and a sensing element of the sensor. However, applicants have found that where a triboelectric sensor is used (at least for purpose (a)), accuracy can be reduced due to charges on dust particles acquired in the space being cleaned and in the duct  20  through which dust laden air is drawn from that space. It has been found that this effect can be reduced by providing an electrical connection between the container being cleaned, the ductwork upstream of the triboelectric sensor and the sensor itself. The connection can be made through a spiral wire on the duct  20  to the fitting by which ductwork  20  is connected to the container. This does not fully eliminate the unwanted charges, but a further improvement can be made by carrying out tests on representative flows of representative dust-laden air through similar duct geometries with actual weighing of the dust content to produce calibration curves relating sensor output to actual flow. Temperature and humidity can also affect accuracy, and by varying and controlling these quantities in such calibration tests, further corrections can be made. The data handling system (described herein by reference to  FIGS. 3 and 41 ) can be provided with the calibration curves in software form. 
     To achieve purpose (b) above, there may be provided one or more triboelectric (or other suitable) sensor(s) at station K, downstream of the cyclone  38 , filters  40  and  42  and blower  46 . In some embodiments, a duct (which may be flexible) may be provided to take discharged gas and residual (i.e. unremoved) particulate well away from the area in which the cleaning operation is taking place. 
     Depending on the gas source, it may be appropriate to provide sensing of gas quality upstream of cleaning lance  12 , for example at stations A or B. At station A, a pressure sensor may be provided to indicate, when cleaning lance  12  is not in use, that gas for blowing is available. 
     Display(s) for displaying measured quantities may be provided on a casing containing the main components shown in  FIG. 2 , or in a separate unit (not shown) connected thereto and in use placed in a position visible to a user. Key operating parameters such as the concentration of particulate matter at the outlet from the space being cleaned are displayed. 
     Regarding purpose (c) above, pressure sensors (not shown) may be provided at stations G, H and I to provide a measure of fouling of filters  40  and  42  with particulates, based on pressure drop through them, so that the need for cleaning can be indicated at an appropriate time. Rather than three such separate sensors, two differential pressure sensors (not shown) may be provided, respectively sensing pressure differences between stations G and H and H and I. 
     Similarly, in some embodiments either another sensor (not shown) is provided to measure the pressure difference between stations F and G, before and after the cyclone  38 , or alternatively separate sensors at stations F and G can be provided. Excessive pressure difference across cyclone  38  can indicate fouling or blockage. 
     It is also possible to provide a pressure sensor at station K in addition to a pressure sensor at station I, so that the pressure change through blower  46  is known, or alternatively to provide a differential pressure sensor to sense the pressure change between stations I and K, i.e. across blower  46 . The speed of blower  46  may be sensed at station J as well. 
     Also in relation to purpose (c), at station L, a sensor (not shown) may be provided to indicate that a certain quantity of particulates has been collected in cyclone separator  38  (or a particulates container (not shown) secured thereto), so that for best operation, cyclone  38  should be emptied. This may be of the optical or infra-red type, that senses interruption of a beam, these sensors being well known in the instrumentation art. Alternatively an ultrasonic type may be used, or even a simple “sight-glass” type indicator or transparent section of cyclone  38  may be provided that can be seen by a user. When a “sight-glass” type indicator is used, an LED light positioned and coloured to minimize glare may be used internally within the cyclone  38  or particulates container to enhance visual clarity. 
     Regarding purpose (d) above, in some embodiments, temperature of the blower  46  Is sensed at station J and/or temperature of gas within space  2  is sensed at station C (or even F), in each case with suitable temperature sensors. 
     Regarding purpose (e) above, during use of cleaning lance  12 , it is desirable that gas pressure in cabinet  4  be maintained at a level that does not lead to significant risk of particulates leakage from the cabinet  4  through for example port assemblies  10  or past seal  7  around door  8 . A pressure in cabinet  4  slightly below external (atmospheric) pressure is suitable in many applications, as it limits the potential for leakage of particulates from cabinet  4 . 
     It is also desirable that during the blowing operation, pressure in cabinet  4  not become too high or too low, to avoid distortion or even structural failure of cabinet  4 . A simple approach is to provide a pressure sensor (not shown) at station C (i.e. sensing absolute pressure within space  2  of cabinet  4 , or the difference between the pressure inside space  2  and the atmosphere). Actual control of the pressure in space  2  is described below. The pressure sensor (not shown) may be located physically on the cabinet  4  or on door  8  with signals communicated to instrumentation and control system  199  via copper cable, optical fibre, wireless or other suitable means. Alternatively, the pressure sensor may be mounted away from the cabinet  4  and communicate with space  2  via a small-bore flexible tube. 
     Regarding purpose (f) above, it is important when blowing gas into an enclosure such as cabinet  4  that there be no leakage of air (and entrained particulates) past elastomeric seals such as seal  7  of cabinet  4 , due for example to seal  7  failing to close off excessive gaps between door  8  and cabinet  4  at positions along the seal  7 . For applications such as that shown in  FIG. 1 ), where a hinged door  8  is sealed by seal  7 , a single sensor (not shown) may be provided to sense whether the door  8  is in the correct position, relative to cabinet  4 , for correct operation of seal  7 . This could be a simple microswitch or a proximity sensor mounted to door  8  or cabinet  4 . If seal  7  is a pneumatic (i.e. inflated) seal, a pressure sensor may be provided to sense pressure in the seal  7 . 
     However, in some embodiments described below, a detachable cover (see for example item  310  in  FIG. 16 , item  310   a  in  FIG. 24 , item  310   b  in  FIG. 33 , item  310   c  in  FIG. 29 ) is used to close off an enclosure or space. In these cases, multiple proximity or other suitable sensors (not shown) may be provided at spaced-apart positions around the cover periphery to enable monitoring of seal operation. These sensors may be of proximity type as above, or be responsive to pressure between the seal and enclosure or electrical conductivity between metallic areas on either side of the seal and facing parts of the enclosure or cover. The sensor locations would correspond for example to stations D and E in  FIG. 2 . 
     If measurement of gas flow rate to lance  12  is required, a flow meter (not shown) may be provided at station B. This could be of any suitable type, for example a venturi section or calibrated orifice plate with sensor(s) to measure the pressure change therethrough (and ideally temperature as well), or a sophisticated thermal sensor such as those available from E+E Elektronik GmbH of Germany. Also, and in the same or any other suitable way, the gas flow rate out of space  2  may be measured. This may be done at station I or station K, where the measurement is unlikely to be influenced by entrained particulates. For applications where concentrations are expected to be sufficiently small, outlet flow rate measurement may be made with sensors at any of stations F, G, H or I. 
     Regarding purpose (g) above, control of the blowing/entraining operation will now be described. 
     In some embodiments, gas flow to the cleaning lance  12  from supply  32  is simply turned on or off as required, by a user, with blower  46  running continuously. The user, as well as monitoring the extent of particulate concentration (visually, or by use of particulate concentration sensor(s) as described above) can monitor pressure in the space  2  if displayed, or simply be alert for alarms based on the sensed pressure in space  2  being, or threatening to be, out of a specified range. 
     A more sophisticated approach in other embodiments is to include in item  52  ( FIG. 2 ) a solenoid valve that can interrupt (or vent to atmosphere) gas flow to cleaning lance  12  automatically if required to prevent overpressure (or loss of appropriate partial vacuum) in space  2 . Similarly, blower  46  can be stopped automatically or slowed down, (or a damper operated) if required to prevent an excessively low pressure in space  2 . The system  199  generates signals to control the blower  46  and/or solenoid valve in item  52 , based on sensed pressure in space  2  or a mismatch of inlet and outlet flow rates. 
     For either of the approaches described in the previous two paragraphs, generation of an alarm and/or of automatic control signals can be anticipatory, based on rate of change of pressure or gas flow rates. 
     In still other embodiments, closed-loop automatic control is used, subject to maintenance of a “fail-safe” capability. For example, cleaning lance  12  may be manually controllable by a user (i.e. with gas flow rate set to off, fully on, or any intermediate value), with blower  46  and/or a variable-flow valve included in item  52  controlled automatically by system  199  to maintain a chosen value (i.e. set point) of pressure in space  2  or net gas flow rate into space  2 . Alarms and/or display of operating parameters may be provided also in these embodiments. For further example, cleaning lance  12  may be simply set to “off” or “fully on”, with closed loop control of a set pressure in space  2 , net flow rate into the space  2 , or a specified flow rate through lance  12 . 
     Note that while maintaining appropriate pressure within a space being cleaned is important, it is to be noted that in many industrial, mining and similar applications, it is unlikely that an excessively high or low pressure will in fact be encountered. This may be, for example because an enclosure being cleaned is itself leaky and therefore an accumulator of particulate matter. Accordingly, in some applications, sophisticated control and even sensing of cleaned space pressure can be safely dispensed with. 
     Referring now to  FIG. 3 , the presence of block  200  indicates the presence of one or more data processing components adapted to provide the functionality described herein. It is to be understood that block  200  may simply comprise a single processor (microprocessor or otherwise) or several processors each covering a subset of the functions required. For example, if there is a closed-loop control functionality as described herein, that may have a dedicated processor. Some or all of the functions carried out within block  200  may be implemented wholly or partially by other means than microprocessors—for example field-programmable gate arrays (FPGAs) may be used to implement some functionalities. Multiple data processing components may be comprised in block  200 , for example, where a variable-flow valve is included at item  52  and has its own internal electronics or where a particulate concentration sensor is provided that has its own data processing components. 
     The data processing componentry of block  200  is provided to receive inputs from sensors and system controls and, using these, to drive a display at  208 , and/or a set of alarms at  210  and, as applicable, control outputs at  207 . It may not be essential for a particular application or embodiment to provide and use all of the sensors described above. For example, in some embodiments reliance may be placed on visual inspection of cyclone  38  to determine that it needs emptying, rather than providing a sensor at station L. However, in general some sensors will be used, and block  202  represents a set of sensor excitation (i.e. powering) and any necessary signal conditioning functions, all as required to convert raw signals from the sensors to a form (digital or analog) suitable for the processing function  200 . (Note that many processors have internal analog-to-digital converters and so can accept analog signals.) The triboelectric sensors of the prototype system described below provide outputs in current-loop form, while the pressure transducers provide digital outputs directly. 
     Block  204  represents presentation of sensor outputs to the processor at  200 . For example in the prototype system described below, a multiplexer is used to provide  8  scannable channels for pressure sensors via the I 2 C bus protocol. Multiplexing of sensor outputs may be provided if there are more sensors used than the number of inputs provided by the chosen microprocessor  200 . Note that as discussed above there may be several sensors at some stations, for example a pressure sensor and a temperature sensor at station C.  FIG. 2  is not intended to suggest a maximum of 12 sensors (A-L). Block  200  may also include any or all of: automated fault detection, diagnostics and datalogging capabilities. 
     System  30  also requires some control inputs provided at block  206  such as on/off switches (not shown) for the blower  46  and the gas supply  32  if it includes a dedicated compressor for example, and to initiate operation of data acquisition by system  199 . If any quantity is to be controlled in closed-loop manner, there may be a control (eg potentiometer) to provide a set point for the mass flow rate. There may also be controls (eg potentiometers in the case of analog control implementation) to set allowed maximum and minimum pressures in the enclosure to be cleaned. 
     Block  207  represents provision of signals required for automatic functions—for example shutting off the gas source  32  if pressure at station C rises too much or a continuous control signal where closed-loop pressure control is provided. 
     Block  208  represents provision of the function of one or more suitable display(s) for visual output of system  30  information as required. For example, there may be display of outputs for particulate concentration from triboelectric sensors at stations F and K. Displays (not shown) may use any suitable technology, for example LED, LCD or OLED. The two last of these may be of a touch screen type arranged to receive any or all of the inputs mentioned in relation to block  206  above. 
     Block  210  represents provision of a separate display of alarm conditions for system  30 . For example, it may indicate that cyclone  38  requires emptying or that filters  40  or  42  have pressure drops indicating that they need cleaning, or that pressure in the enclosure being cleaned is outside its set limits, risking damage or particulates leakage. Such alarm functions may actually be incorporated in and displayed on the display  208 , or may be provided separately, for example using a known “traffic light” format (not shown) based on green, yellow and red LEDs to indicate respectively—no alarm or normal operation, warning, alarm condition. 
     The following is a list of conditions and responses that may be automatically recognized and caused within block  200  to generate alarms or control signals that provide system  30  with a “fail safe” capability.
         Excessive particulate contents at either inlet or outlet of blower  46 —shut down blower, provide diagnostics.   Where intention is to operate at negative pressure—pressure excessively low (with risk to structure) or not low enough (risking leakage of particulates). If not low enough, interrupt flow into the enclosure, also check blower, filter(s) cyclone fouling. If too low either stop blower or reduce blower speed.   Where positive pressure in enclosure  4  is allowed—pressure excessively high risking structural damage or leakage of particulates. Interrupt flow into enclosure, increase blower speed, check for fouling of filter(s) or fouling or filling of cyclone(s).   Fouling of filter(s)—stop operation of system.   Fouling or filling of cyclone(s)  38 —stop operation of system.   Blower  46  temperature excessive—stop operation of system.   Blower  46  not operating or underspeed—stop operation of system.   Where seal  7  is a pneumatic seal—seal pressure out of allowable range—stop operation of system.   Where seal  7  is pneumatic or non-pneumatic—any one or more of seal position measurements (if sensors fitted) out of allowed range. (Or if pressure sealing pressure sensor(s) fitted, any one or more of their outputs out of range. Stop operation of system.       

     Block  211  represents the writing of sensor and other data to some form of storage. For example, the prototype system described below is provided with a facility to write data based on sensor outputs to an SD card for later downloading and checking. In that system, all active sensors are scanned cyclically once the system is in operation and derived outputs from them are time stamped using a real-time clock module and written to an SD card. 
     Block  213  represents communication of data to location(s) away from the worksite and receipt of instructions and/or the like from external sources. For example, where a service provider wishes to provide checking and certification of critical particulate removal operations from a location away from the site of the operation, it is possible to provide a communications interface for the transmission and receipt of data and instructions. As an example, a mine may have a wireless packet-switched digital data network covering its entire site that can be used to communicate with a base station, and that base station may communicate via the mobile phone network or via the internet by whatever other connection means is available. Where mobile phone network accessibility is available at a worksite, it may be used and the base station may not be necessary. The service provider may carry responsibility for correct functioning, calibration and the lie for the equipment used for particulate removal, and receipt of data from the various sensors described facilitates this function. Data and instructions may be transmitted substantially in real time or data may be written to memory (eg using an SD card) by system  199  for later transmission. 
     Note that although the above disclosure has referred to particulate removal, it is possible to use the apparatus as shown in  FIGS. 1( a ) ,  2  and  3  for purging of gases from enclosed spaces, either as an alternative to particulate removal or in any application where both particulates and undesired gas are both present. An online gas analysis device suited to the gas in question may be provided at for example any of stations F, G, H, I or K, instead of or in addition to a particulate concentration sensor. 
     Ways to arrange for the methods of  FIGS. 1( a )  and  1  ( b ), and the operation of system  30  (including system  199 ) to be applied to other enclosures will now be described. 
     Example—Application to Cabinets 
       FIGS. 4 to 10  show one way in which a typical existing cabinet  60  for electrical components (not shown) can be modified to implement the invention using cleaning system  30 , cabinet  60  corresponding to enclosure  4  in  FIGS. 1 and 2 . Cabinet  60 , is a cabinet such as might typically be found in an industrial facility or in heavy mobile equipment such as a locomotive or mining haul truck, and has a fixed main portion  62  defining enclosed upper and lower spaces  64  and  66  respectively for electrical components. Cabinet  60  has been modified to enable cleaning of particulates using the invention, but only in respect of the upper space  64 . 
     Closure of opening  68  of lower enclosed space  66  is provided by a conventional hinged door  70  normally held closed by a handle-operated latch  72 . A peripheral elastomeric seal  74  mounted to main portion  62  extends around opening  68  to limit ingress of contaminants such as particulates when door  70  is closed. 
     Normally, cabinet  60  would have a hinged door essentially the same as door  70  except for its dimensions being suited to close opening  76  of upper space  64 , and also a similar peripheral sealing arrangement. However, according to the modification, a rectangular frame  78  is secured (for example by welding at  81 ) to main portion  62  and extends peripherally around opening  76  of the upper space  64 . A hinged door  80  is supported on frame  78  and can be opened to allow access to upper space  64  when required. Door  80  is received in frame  78  and held closed by handle-operated latches  82 , and contaminant ingress and between door  80  and frame  78  is limited by a peripherally extending elastomeric seal  84 . Because cleaning can involve temporarily increasing pressure in upper space  64 , door  80  includes a reinforcing member  79  extending around its periphery. 
     Door  80  has features that enable the invention to be implemented for cleaning of upper space  64 . 
     First, door  80  is provided with port assemblies  86  (corresponding to port assemblies  10 ) through any of which cleaning lance  12  can be pushed partway into upper space  64  at in the way shown for enclosure  4  in  FIG. 1( a ) . Door  80  also has a transparent viewing window  88  corresponding to window  22  in  FIG. 1( a ) . 
     Second, for removal of particulates from upper space  64 , at least one outlet port  90  (corresponding to outlet port  18  in  FIG. 1( a ) ) for gas and entrained particulates is provided in door  80 . This has a removable cover  92  that can close outlet port  90  when cleaning is not underway. Duct  36  is secured to outlet port  90  for use when cleaning upper space  64 . Outlet port  90  is provided in door  80 , however in some embodiments (not shown) it may be provided (or an additional outlet port may be provided) at a suitable location in cabinet main portion  62 . 
     In  FIG. 6 , one of port assemblies  86  is shown in exploded fashion. One or more discs  94  of gas impermeable elastomeric material (for example formed from an artificial or vulcanized natural rubber) are provided, each with a slit  96  extending across part of a diameter, and discs  94  are arranged in layered fashion with slits  96  oriented in different directions as shown. Discs  94  are secured against the door  80  by a ring  98  using fasteners (not shown) extending through holes  100  in ring  98  and door  80 , ring  98  being concentric with a hole  102  in door  80 . Port assemblies  86  can be reasonably (not absolutely) gas- and particulates-tight when not in use. Cleaning lance  12  can be pushed through slits  96  so that its nozzle  14  is inside the enclosure, while the gas supply hose  34  remains outside cabinet  60 . Moreover, cleaning lance  12  can be rotated about its length as required, its angle to the door  80  varied, and the distance beyond door  80  to nozzle  14  can be varied by a user as required. The number of port assemblies  86  on door  80 , and their positions, may in some embodiments be chosen to suit the arrangement of components within the enclosure  60  to enable most effective and thorough cleaning. 
     Note that the use of frame  78  as shown in  FIGS. 4 to 10  is a measure that was adopted for the particular cabinet  60  described here, which had inadequate gas and particulates sealing around door  80 . For a cabinet and door having adequate sealing arrangements (not shown) the door features described above may be able to be implemented by simply modifying the original door. 
     As shown in  FIG. 15 , the cleaning lance  12  may have a collar assembly  170  securable in any of a range of positions on tube  13  so as to prevent excessive penetration of cleaning lance  12  into the enclosure (for example cabinet  60 , cabinet  150  or enclosure  4 ), leading to potential damaging of components therein. 
     Alternatives to the port assemblies  10  shown in  FIGS. 4 to 10  are possible. One such is shown in  FIGS. 11 and 12 .  FIG. 11  shows a port assembly  200  secured to an enclosure door  202  (similar for example to door  80  or door  8 ) and providing access for cleaning lance  12  to an internal space  204 . Port assembly  200  comprises an elastomeric bellows or boot  206 , secured to door  202  by a ring  208  and fasteners  211 . Secured to bellows  206  is a block  210  through which, in use, tube  13  of cleaning lance  12  can pass. Tube  13  can slide lengthwise in, and rotate relative to, block  210 , and be angled in horizontal and vertical planes as shown by arrows  214 , and sealing between tube  13  and block  210  is provided by an elastomeric O-ring seal. Other seal arrangements may be used depending on the application (eg lip seals, multiple seals). When port assembly  200  is not in use, a lid  216  is screwed onto a threaded portion of ring  208 , after withdrawal of tube  13 , to prevent gas and particulates egress. (Note that a lid (not shown) equivalent in function to lid  216  could be screwed to block  210  instead of ring  208 .) Port assembly  200  requires that any nozzle  14  comprised in cleaning lance  12  be of lesser diameter than tube  13 , so that tube  13  can be entered through block  210 . 
     Alternative Embodiments—Cover Assemblies 
     Further alternatives to the arrangements that were described above by reference to  FIGS. 4 to 10  will now be described. 
       FIGS. 4 to 10  showed a permanent modification to an existing cabinet  60  to implement the invention, in which a frame  78  was secured to a main portion  62  of the cabinet  60 , the frame  78  itself incorporating a door  80 . Another approach applicable to cleaning of cabinets with hinged doors will now be described. This is to provide a temporary cover which can be secured sealingly over the opening of the cabinet after either removing or swinging open the cabinet&#39;s existing door. 
       FIG. 13  shows in a view equivalent to  FIG. 9  a temporary cover  77  comprising a frame  78   a  that is exactly the same as frame  78  in all respects, including provision of a door  80   a  equivalent to door  80 , except that frame  78   a  lacks a member equivalent to member  83  (see  FIG. 9 ) secured to cabinet portion  62  at  81 . Instead, a retaining member extending peripherally around frame  78   a  is provided together with an elastomeric seal  87 , also extending peripherally around frame  78   a . When particulates are to be dislodged by use of cleaning lance  12 , cover  78   a  is temporarily secured to cabinet main portion  62 , being held in place by suitable clamps (not shown), the original door (not shown) of cabinet  60  being swung aside or removed altogether. Seal  87  may be inflatable with a gas to enhance its sealing action. When cleaning is complete, frame  78   a  is removed. 
       FIG. 14  shows a view (in vertical section) of a cabinet  150  fitted with an alternative temporary cover  152  for cleaning. Cover  152  is secured by suitable clamps  154  on its periphery. Cover  152  is sealed against cabinet  150  by a peripheral seal  156 . This may if desired be of a type inflatable by gas. Cover  152  has port assemblies  158  which may be the same as port assemblies  10  and a gas-and-particulates outlet port  160  for connection of duct  20 . Cover  152  has a dished shape (as seen in the section of  FIG. 14 ) to provide more room between the port assemblies  158  and components  162  in cabinet  150  than would be provided by for example cover  78   a . Where practicable, this shape can be advantageous in enabling easier and better positioning of cleaning lance  12  and reduced risk of contact with and damage to components in cabinet  150 . Further, cover  152  is formed from a substantially transparent plastics material (eg polycarbonate or acrylic) to provide for easy visibility of the cabinet interior while cleaning lance  12  is in use. Anti-scratch treatments are known in the art and may be applied to at least the inward surface of cover  152 . Still further, a set of light-emitting components (eg LEDs) is provided inside the space  164  formed by cabinet  150  and cover  152  to enhance visibility within space  164 . (This approach to lighting is applicable also to other embodiments, such as those shown in  FIGS. 4 to 10 and 13 .) Cover  152  is shown without a door equivalent to door  80   a  of cover  77  but a hinged door could be provided in cover  77  if desired (not shown). 
       FIG. 16  shows still another temporary cover  310  that is an alternative to those described above. A cabinet  300  has an internal space  302  that is to be cleaned of particulates. Cabinet  300  has a flange  304  surrounding an opening  306  that in ordinary use of cabinet  300  would be closed by a door or other cover. (No such door or cover is shown in  FIG. 16 .) Hinges  308  could for example support such a door that either is simply swung open or removed from cabinet  300 . To cover opening  306 , cover  310  is provided. 
     Cover  310  has a formation  312  on its upper edge  314  that can be hooked over an upper part of flange  304  when cover  310  is moved in the direction of arrows  305  towards flange  304 . Cover  310  is then held in position over opening  306  by clamps  316 . Extending around the periphery of cover  310  is a seal  318  that in use of cover  310  bears sealingly against flange  304  to prevent or limit passage of particulates from internal space  302  during cleaning (similarly to seal  84  of  FIG. 8 ). Seal  318  is of rubber or a rubber-like material and may optionally be of a pneumatic type inflated with a gas. (A seal (not shown) serving the same purpose as seal  318  may, in alternative embodiments, be provided on an enclosure being cleaned for use with a cover otherwise equivalent to cover  310 . Further, such a cover or a cover with a seal such as cover  310  may instead of being hung from a flange (such as flange  304  in  FIG. 16 , be hung from a suitable temporary or permanent formation specifically provided.) 
       FIG. 17  shows one of the clamps  316 . This has a magnet  322  that in use holds itself against surface  307  of cabinet  300 , and captive thereon a bolt  324  passing through cover  310 . A wingnut  326  can be screwed on bolt  324  to move cover  310  towards surface  320 . Bolt  324  passes through a compression coil spring  325  between the magnet  322  and cover  310  to aid correct positioning of magnet  322  when cover  310  is being positioned ready for use. 
     Any other suitable clamp arrangement can be used as an alternative to clamps  316 . In other embodiments, where control of pressure within an enclosure being cleaned is sufficiently reliable, to maintain a negative pressure within that enclosure at all times and dispense with some or all clamps such as clamps  316 . The cover  310  is then held in place entirely or partially by atmospheric pressure due to the lesser pressure inside the enclosure. Another approach (not shown) as an alternative to clamps  316  is to provide magnetic tape to cover  310  extending around all or part of the periphery of cover  310  so as to be attracted to (for example) flange  304 . Still another approach (not shown) is to provide discrete magnets recessed into cover  310  on its enclosure-facing side that are positioned to be abut flange  304  and be held by the magnets against it. 
     While port assemblies of the types described above (i.e. items  10 ,  200 ) may be used for cover  310  for insertion of a cleaning lance such as lance  12 , cover  310  is shown with port assemblies  340  of a further type. Cover  310  has multiple openings  330  each covered (on the outer side of cover  310 ) by a movable cover  332 , as shown in  FIGS. 18 and 19 . Movable cover  332  acts as a restriction to flow and possible particulate leakage through opening  330  when the port assembly  340  is not in use accommodating a lance  12 . Openings  330  are bevelled at  331  to accommodate a range of angular movement of lance  12 . Each cover  332  is supported on a pivot pin  334  so as to be freely swingable about an axis  336  by a user to uncover the associated opening  330 . A cleaning lance such as cleaning lance  12  can then be inserted through the opening  330  in the same way as shown in  FIG. 1( a )  for use in blowing gas into internal space  302  to dislodge particulates therein. Thus, each combination of an opening  330 , cover  332  and pivot pin  334  amounts to a port assembly  340  analogous to a port assembly  10 . Port assemblies  340  are simpler than port assembles  10  and  200  and are suitable for use where it is intended that the internal space of a cabinet (or other enclosure) being cleaned will be held at a lower pressure than the surroundings of that cabinet enclosure. The low pressure at least limits any escape of particulates from the space  302  through port assemblies  340 . Although not shown, it would be possible to provide a seal (for example an O-ring) surrounding opening  330  in either cover  332  or cover  310  to better seal cover  332  against cover  310  when the pressure is lower in the internal space than outside. 
     Cover  310  is shown as made from a sheet of transparent or at least translucent material, which is advantageous because a user has better visibility of what is happening inside the enclosure being cleaned. Suitable polycarbonate plastics materials can be used, for example, and may be treated with a scratch-resistant treatment as known in the art. Alternatively (not shown) a window (similar to window  88 ) may be provided, with cover  310  being otherwise non-transparent. 
     Cover  310  is shown with an outlet port  346  similar to outlet port  18  of  FIG. 1( a ) , for connection of a duct (not shown) to be held at low pressure and receive gas and entrained particulates gas from the enclosure being cleaned. 
       FIG. 24  shows a cover  310   a  that is an alternative version of the cover  310  also positioned ready for securing to cabinet  300 . Parts of cover  310   a  that are, and that function, the same as corresponding parts of cover  310  are indicated by item numbers including the suffix “a” and are not described again here. Cover  310   a  has several differences from cover  310 , as follows. First, cover  310   a  comprises a central portion  311  and two side portions  313  and  315 , that are hinged to central portion  311  by “piano”-type hinges  319  and  317  on the outward-facing side of cover  310   a . This enables cover  310   a  to be folded, so as to be easier than cover  310  for one person to carry. (However, it is to be noted that hinges such as  317  and  319  preferably avoided where folding is not necessary as having no hinge is simpler.) Formation  312   a  is shorter than formation  312  of cover  310 , extending only along a top edge of portion  311 , to enable folding. Second, cover  310   a  has no attached seal corresponding to seal  318  of cover  310 . Instead, a seal  321  is secured to, and extends around, flange  304 . This may be either a pneumatic seal with an inflating connection  323 , as shown, or a non-pneumatic elastomeric seal (not shown). To provide an adequate seal on cover  310   a  itself instead of flange  304 , would be problematic due to the feature of folding. The chain-dotted outline  321   b  in  FIG. 24  does not represent an actual component, but the area on cover  310   a  that is contacted by seal  321  when cover  310   a  is secured on cabinet  300 . Note: cover  310   a  is shown with a different number and arrangement of port assemblies  340   a  from cover  310 , but this is simply a matter of choice for any particular application. 
     While various embodiments of cabinet doors and enclosure covers have been described above, it is to be understood that particular features of any one may where practicable be combined with features of another. For example, LED lighting may be used in any of the designs described above, as may any of the port assemblies  10 ,  200  or  340  or the “dished” shape of cover  152 . 
     Alternative Embodiments and Applications 
     Instead of a manually-manipulated and operated cleaning lance  12 , some further embodiments provide for mechanical means for moving gas nozzle(s). Examples will now be given. 
       FIG. 20  shows an enclosure  100  in a view equivalent to  FIG. 1( a ) . Nozzles  102  are mounted to, and able to rotate on, manifolds  104  that are in turn secured by brackets  106  to door  108 . Manifolds  104  are supplied with gas from an external source (not shown) via conduits  110  that extend through door  108 . Rotating seals (not shown) enable gas to flow from manifolds  104  into nozzles  102  even as nozzles  102  oscillate about manifolds  104 . Conduits  106  are connected to an external manifold  112  on door  108 . A rotating crank member  114  connects via a link  116  to a link  118  that can oscillate nozzles  102  about manifolds  104  through a range of angles as shown by arrows  120 . Crank member  114  extends sealingly to the exterior of enclosure  100  and is rotated manually or by a motor (not shown). Gas with entrained particulates is drawn from enclosure  100  through a duct  122  equivalent to duct  20  of  FIG. 2 . There are several nozzles  102  on each manifold  104 . Alternatively, an “air knife” type nozzle, not shown, elongate along the length of each manifold  104  may be provided instead of nozzles  102 . 
     In a still further alternative shown in  FIG. 21 , a single “air knife”  124 , so-called, that is elongate across the width of an enclosure  126  may be provided and arranged to be fed with gas from an external supply and to produce a flow of the type shown by arrows  128  in  FIG. 21 , with the air knife  124  being able to traverse up and down (as shown by arrows  130 ) and to oscillate around an axis  132  extending lengthwise of the air knife  124 . A suitable mechanism (not shown) could readily be provided by a person skilled in the art and enable such motions to be provided. Duct  134  extracts gas and entrained particulates from enclosure  126 . 
     In each of the arrangements shown in  FIGS. 20 and 21 , the system external to the enclosures  100  and  126  is in some embodiments the same as system  30  described above except for absence of cleaning lance  12 . In some embodiments, the arrangements shown in  FIGS. 20 and 21  are provided with motorized and automatically controlled positioning of the nozzles ( 102  or air knife  124 ), such positioning being under the control of microprocessor  200  or a separate microcontroller (not shown). In these embodiments, item  207  in  FIG. 3  includes control outputs for any or all of positioning, orienting, movement speed control, and gas flow control for nozzles  102  or air knife  124 . 
     Positioning and orientation of the nozzles  102  or air knife  124 , the flow rate of gas through them, and traversing speed may all be controlled by processor  200  to execute a pre-defined or programmed cleaning scheme input by a user, with instructions stored in a memory (not shown) accessible and executable by the processor  200 . In some embodiments, the scheme may be executed repeatedly until a preset acceptable level of particulate concentration is achieved at the gas outlet from the enclosure  100  or  126 . In other embodiments, multiple cleaning schemes may be entered with provision for execution of several of them where one only does not lead to acceptable particulate concentration at the outlet. 
     In some embodiments, a user may enter multiple schemes for different requirements, such as for example a fastest satisfactory clean or a most thorough clean. 
     Cleaning schemes may include instructions to cause nozzles  102  or air knife  124  to dwell at specific locations and orientations for preset times or until particular outlet particulate levels are achieved. Provision may be made for sudden variations in gas flow through the nozzles  102  or air knife  124 . 
     In some embodiments, processor  200  is adapted to record and store a manually executed cleaning and thereafter execute that scheme whenever cleaning is subsequently required. 
     In some embodiments, processor  200  executes a randomly or pseudo-randomly selected series of movements and re-orientations of nozzles  102  or air knife  124  until a satisfactory outlet particulate level is achieved. The scheme thus executed may be recorded for future automatic repetition in future under processor  200  control. 
     In some embodiments, processor  200  may be programmed to automatically execute a number of random or pseudo-random schemes and select the best according to a specified criterion, such as lowest particulate level achieved, or least time to reach a specified outlet particulate level. It is further possible to provide for machine learning, by providing for replacement in memory of a previously stored cleaning scheme by one recorded (for example when manually executed by a user or in additional random or pseudo-random cleaning schemes) that achieves an improved result. 
     An embodiment will now be described that provides for cleaning of an open-top rail car (for example of the type used for transport of coal or other minerals) or the like, and that involves essentially the same principle as the embodiments described above. A problem with such rail cars is excessive particulates remaining in the car after emptying, these particulates later being disturbed when the empty car is in motion and so polluting the environment. 
       FIG. 22  shows a typical open top rail car  400  whose upper part, comprising a load containing space  402 , is shown in longitudinal section. A tubular-section rail  404  extends around the top of the rail car. At a location where the car  400  is to be cleaned, a platform-like cover  410  is provided that when cleaning is to be carried out can be positioned over car  400  and lowered (in the direction of arrows  406 ) onto the rail  404  from above, whereby to close space  402 . An elastomeric seal  412  contacts rail  404  after such lowering. 
     A carriage  412  moves lengthwise of the car  400  on a rail  414  (propelled for example by an air motor (not shown)) and has mounted thereon one or more nozzles  420  for blasting internal surfaces of space  402  with air (or other gas) supplied through a hose  416  and gas inlet  418 . 
     To remove air (or gas) and entrained particulates from space  402 , one or more ducts  422 , of which four are shown, are provided on the underside of platform  410  and extend downward into space  402 . Ducts  422  communicate with a manifold  424  from which air (or gas) and entrained particulates are drawn at  426  by a vacuum source (not shown). Internal space  402  may be kept during cleaning at a pressure below atmospheric. 
     When cleaning is complete, cover  410  is lifted upward to clear rail car  400 . The arrangement shown in  FIG. 22  may be used in a building (not shown) with ends through which cars  400  (or other vehicles where applicable) are sequentially driven with lifting of platform  410  effected by a fixed lifting equipment in the building. Alternatively, a truck or specialized vehicle (not shown) with a pivoted or articulated arm may be used to manipulate platform  400  and associated equipment as required for cleaning. 
     Other types of container or enclosure are not open-topped but rather open at an end. As an example,  FIGS. 25 and 26  are longitudinal central sections on standard shipping containers. (Some detail of these containers has been omitted, including doors.) 
     In  FIG. 25 , container  600  is closed by a cover  602  that fits into its open end when the outward-opening doors (not shown) are opened. Cover  602  is sealed against gas and particulate movement by a peripheral seal  604  that extends wholly around cover  602  and seals against inner surfaces (floor  606 , walls  608  and ceiling  610 ) of the container  600 . Seal  604  may be a pneumatically inflated seal. Sealing is not against end surfaces of container  600  because of the presence thereon of latch fittings (not shown). In container  600  is a support carriage  612  movable under user remote control on wheels  614 , and that has a gas nozzle  616  that can be remotely controlled by a user, outside container  600 , to move in a range of ways, as indicated by arrows  618 . Gas is supplied to nozzle  616  by a conduit  620  (including a hose portion) connected through cover  602  to a gas source (not shown) so that a jet of the gas can be used to dislodge and entrain particulates. Carriage  612  is also fitted with at least one inlet  622  for gas and entrained particulates, that in turn is connected via a flexible outlet duct  624  to a system (not shown) equivalent in function to system  30  of  FIG. 2 . A window  623  is provided in cover  602  so that the user (not shown) can see and guide the carriage  612  as required until the monitored concentration of particulates leaving the container  600  is sufficiently low. Suitable lifting and manipulation equipment (not shown) is provided for positioning carriage  612  and then cover  602  for use, and for subsequently removing them from container  600 . 
       FIG. 26  shows an alternative arrangement in which a cover  626  is fitted into an end of a shipping container  628  in essentially the same way as cover  602  is fitted to container  600 . A pneumatic or other suitable seal  603  equivalent to seal  604  is provided to prevent escape of gas and particulates around the periphery of cover  626 . A nozzle  629  directs a jet of gas to dislodge and entrain particulates in the same way as nozzle  616  and is movable under user remote control in a range of ways as indicated by arrows  630 . A gas supply (not shown) external to cover  626  is provided and supplies nozzle  629  through a hose  631 . Nozzle  629  is supported in this embodiment by a structure  633  secured to cover  626 . This is shown as a multi-section telescopic arm, but other arrangements will readily suggest themselves to persons skilled in the art. Exhaust inlets  632  are provided on a structure  634  that is also secured to cover  626  and that incorporates outlet ducting for gas and entrained particulates. A window  635  is provided in cover  626  for a user outside container  628 . Not shown in  FIG. 26  is a system equivalent in function to system  30 . Suitable manipulating equipment (not shown) is provided to enable cover  626  and the components secured to it to be entered longitudinally (i.e. in the direction of arrow  637 ) into container  628  and later removed. 
     Although standard shipping containers have been referred to in relation to  FIGS. 25 and 26 , other types of enclosures could be suitable for similar arrangements. For example, some road vehicles (not shown) have enclosures with end doors, and the arrangements shown in  FIGS. 25 and 26  could apply to them. 
       FIG. 27  shows a still further application similar to that described above by reference to  FIG. 26 . A container  650  (such as for example a plastics barrel of the type used for solid-phase chemicals) is temporarily closed by a cover  652  that is sealed to the container  650  by a suitable peripheral seal  654  (pneumatic or otherwise). Cover  652  has a gland  656  through which there passes sealingly a gas inlet duct  658  through which an external gas source (not shown) supplies gas to a nozzle  660  within container  650 . Nozzle  660  is able to be moved angularly as shown by arrow  662 , and the duct  658  is able to be both traversed up and down (as drawn) and rotated as shown by arrows  664  and  666  respectively. The movements of the nozzle  660  and duct  658  are controlled either by an automatic mechanism (not shown) or manually by a user whereby a jet of gas from nozzle  660  can be directed over the entire internal inner surface  668  of container  650 . Also extending through the cover  652  into container  650  is an outlet duct  670  through which gas and entrained particulates are drawn out. Also provided is a system (not shown) equivalent to system  30 , for providing gas to duct  658  and drawing out, treating and monitoring gas and articulates flowing through duct  670 . 
       FIG. 23  shows an assembly  500  usable in some embodiments of the system  30  shown in  FIG. 2 , specifically comprising elements  40 ,  42  and  46 . Assembly  500  comprises a firstly centrifugal fan (blower)  502  corresponding to blower  46  in system  30 . Fan  502  is coupled to and driven by a shaft (not visible) of an electric motor  504 . Gas enters assembly  500  through an inlet port  506  after leaving cyclone separator  38  and so contains less particulates than at outlet  18 . From inlet port  506  the gas enters a plenum chamber  508  and then passes through a filter bag  510  that is supported by a ring  512  at its upper end in a cylindrical casing  514  which is shown partially sectioned. Filter bag  510  corresponds to filter  40  of system  30  and may comprise a woven textile or unwoven material (as known in the filter art) suitable for catching particulates while the gas passes through it and into an outer space  520  of casing  514 . From space  520 , the gas then enters a modular HEPA filter  518  (corresponding to element  42  in  FIG. 2 )), thereafter passing into fan  502  and out through outlet  536  (corresponding to outlet  53  of system  30 ). Casing  514  may advantageously be formed from a transparent plastics material so that any fouling of space  520  by particulates becomes apparent to a user. 
     Removal of filter bag  510  for emptying or disposal can be effected through a lid  522  at the top (as drawn) of the plenum chamber  508 . Bag  510  is preferably of conical shape and proportioned to at least approximately equalize along its length the flux of gas through its surface. 
     To hold the parts of assembly  500  together securely and sealingly against gas and particulates leakage and enable easy disassembly when required, casing  514  is fitted with a flanged ring  524  and a base plate or ring  526  is provided at an end of motor  504 . Spaced circumferentially around and extending between and through ring  524  and plate (or ring)  526  are several (for example three) tension members  528  which once placed in tension hold together the fan  502  and motor  504 , HEPA filter  518 , and casing  514 . Members  528  may be for example solid rods threaded at each end for nuts or (as shown) lengths  530  of wire rope with threaded end fittings  532  swaged on at each end and secured by nuts  534 . 
     Motor  504  has its own integral air pump (not shown) for cooling with inlet  536  and outlet  538  separate from the gas flow circuit of system  30 . 
     Assembly  500  is convenient for some embodiments and applications, including where components of system  30  are provided in a backpack (not shown). 
     Further Cover Assembly Embodiments 
     Yet another cover  310   c , shown in  FIG. 29  and similar to cover  310   a  (shown in  FIG. 24 ) will now be described. Cover  310   c  has a number of features that differ from features present in cover  310   a . Parts of cover  310   c  that are, and that function in essentially the same as corresponding parts of cover  310   a  are indicated in  FIG. 29  by item numbers that are the same as those corresponding parts with an added suffix “c” so as to not need further explanation. Thus, for example, items  312   ac  in  FIG. 29  do for cover  310   c  what items  312   a  do for cover  310   a , namely allow cover  310   c  to be hooked over an upper part of a flange of a cabinet (not shown). 
     Instead of being made in three panels  313 ,  315  and  311  connected by two hinges, cover  310   c  has two panels  802  and  804  connected by a single hinge  806 . (Of course, hinge  806  may be omitted altogether where foldability is not required.) Panels  802  and  804  are flat and may be of a suitable translucent or transparent sheet plastics material. Port assemblies  340   ac  are provided, but in different locations from the port assemblies  340   a  of cover  310   a  that facilitate folding of the two panels  802  and  804  flat against each other when cover  310   c  is not in use. Not shown, but another possibility, is to provide port assemblies  340   ac  in locations tailored to allow best access to items (not shown) in enclosures on which cover  310   c  will in use be deployed. 
       FIG. 30  shows a particular port assembly  808 , comprising a cover portion  810  that threadably engages with a collar  812  secured gas-sealingly to panel  802 . Cover portion  810  can be screwed into or out of collar  812  as required using handle formations  816  and has an opening  814  that allows a lance (such as lance  12 ) to be pushed into an enclosure (not shown) on which cover  310   c  is secured. The other port assemblies  340   ac  have collars (not shown) the same as collars  812  and cover portions  818  the same as cover portion  810  except that no opening corresponding to opening  814  is provided. These cover portions  818  have annular elastomeric seals (not shown) the same as seal  820  of cover portion  810 . 
     Instead of a single port for extraction of gas (like port  346   a  of cover  310   a ) cover  310   c  has two ports  821  and  822  that are in fluid communication with chambers  823  and  824  on the sides of panels  802  and  804  respectively that in use of cover  310   c  lie in the opening of an enclosure (not shown) to be cleaned. Chambers  823  and  824  have internal spaces  825  and  826  respectively. (Chambers  823  and  824  are shown in  FIG. 29  as they would be seen through transparent panels  802  and  804 .) 
     Chamber  823  (the same as chamber  823 ) is shown in section in  FIG. 31 . Space  825  is defined by walls  827 ,  828  and  829 . Wall  828  has elongate slots  829 , so that entry of gas and entrained matter is through multiple slots  829  as shown by arrow  830 . This arrangement provides for better removal of entrained matter than a single position port such as  346   a . Item  831  is a portion of an enclosure to which cover  310   c  could be secured for use. Flexible duct  832  (corresponding to duct  20  of  FIG. 1 ) is shown in  FIG. 31  as positionable sealingly by an end fitting  833  enterable into port  821 . Because there are tow ports  821  and  822 , two such ducts are required and may be joined into a single flexible duct (not shown) by a suitable fitting. The essential here is that gas and entrained particulate matter can be collected at multiple points with an enclosure being cleaned. 
     Still further arrangements for effective removal of gas and entrained particulates will readily suggest themselves to persons skilled in the art. 
     Referring to  FIG. 2 , in practical realisations of the invention, many, most or all of the sensors provided may be in an enclosure that is separate from the enclosure being cleaned and connected to the latter by the conduits  34  and  20 . However, the measurement of pressure within the enclosure being cleaned is particularly important and sensing of that pressure may be done at a point within the enclosure being cleaned. As an alternative to a sensor at a station such as station C ( FIG. 2 ) with an electrical connection for its output to an enclosure containing the other components left of station “XX” in  FIG. 2 , it is possible instead to provide an orifice opening into the enclosure being cleaned and in fluid communication through a flexible tube with a sensor (pressure transducer) located in the enclosure containing those other components.  FIGS. 32 and 33  show two ways to do this. 
       FIG. 32  shows an enclosure  900  being cleaned, with a duct  901  (corresponding to duct  20  of  FIG. 2 ) connecting the interior of enclosure  900  to an enclosure  902  containing the components shown to the left of station “XX” in  FIG. 2 . Duct  901  is of the known type having a flexible tube  910  held open by a spiral formation  911  such as a wire. 
     A small-diameter tube  904  enabling an orifice  905  open to the interior of the enclosure  900  to connect to a sensor  906  in enclosure  902  may conveniently be provided inside the flexible duct  901 , with the tube  904  terminating in the orifice  905  in a fitting  903  by which the duct  901  is secured to the enclosure  900 . At its other end, tube  904  terminates at a fitting  913  with a passage  914  in fluid communication with a pressure transducer  906  in enclosure  902 . 
     Another possibility is to eliminate tube  904  and provide instead that the duct  901  is again of the type having a flexible tube  910  held open by a spiral formation  911 , but in which that spiral formation is itself hollow along its length, so as to be in effect a small-diameter tube. The orifice  905 , in fitting  903 , is in this case in fluid communication with the hollow interior (not shown) of the spiral formation  911 . At the other end of the duct  901 , the spiral formation  911  and its interior (lumen) is in fluid communication via passage  914  in fitting  913  with the pressure sensor  906  in enclosure  902 . 
     In each of these two arrangements, it is appropriate to provide at the orifice that opens into enclosure  900  a plug or cover, for example of sintered metal, (not shown) adapted to prevent clogging of the orifice, which could adversely affect the pressure measurement. 
     Further Embodiments—Cover Assemblies 
     To disclose yet further additional options for covers according to the invention,  FIG. 33  shows a cover  310   b  that is an alternative to covers  310 ,  310   a , and  310   c . Cover  310   b  comprises a single transparent plastics panel  1024  shaped and proportioned to fit over an opening into an internal space of an enclosure (not shown). Cover  310   b  is provided with multiple ports  1012  of the type shown in  FIGS. 18 and 19 , located specifically in positions that provide optimal access for a cleaning lance such as lance  12 . There is also a port  1020  that in use of the cover  310   b  receives an end fitting  1026  of an outlet conduit  1002  for gas and entrained particulate matter that corresponds in function to conduit  20  of  FIG. 2 . 
     Banks  1018  of light emitting diodes (LEDs) are provided on the internal-space-facing face of panel  1024  for internal lighting of the internal space. The LEDs are protected by transparent or translucent elongate covers glued or otherwise secured to panel  1024 . Extending around the periphery of panel  1024  is a seal  1016  that in use of cover  310   b  lies between panel  1024  and a facing part of the enclosure being cleaned. Seal  1016  may be formed from rubber or a rubber-like material or other material (for example felt) to provide at least some degree of sealing against gas and particulate leakage as cover  310   b  is pushed against the enclosure by the difference between atmospheric pressure and the partial vacuum maintained in the enclosure. Perfect sealing is not essential where there is a p[atrial vacuum in the enclosure. 
     Two additional provisions are made for holding the cover  310   b  in place. First, magnets  1014  are secured in recesses in panel  1024  and pull panel  1024  toward the enclosure (if it is ferromagnetic). Second, a formation  1010  is provided whereby the cover  310   b  can be hooked onto an upper edge of a flange (not shown) on the enclosure, in the same way as described for covers  310  and  310   c.    
     Two forms of sensor are provided on cover  310   b . First, a pressure sensor  1022  is provided for sensing pressure inside the enclosure, having a pressure-sensitive diaphragm or surface (as opposed to a small hole leading to such diaphragm or surface) so as to be immune from clogging with particulate matter. Second, at each port  1012  there is provided a sensor (not shown) that indicates whether the port is “open” (i.e. in use to accommodate a cleaning lance such as lance  12 ) or closed. The sensor may be of any suitable type for example a microswitch or Hall effect proximity sensor actuated by a movable portion of the port assembly, such as movable covers  332  of port assemblies  340 ). 
     The functionality of instrumentation and control system  199  of  FIG. 3  may be expanded to include sensing of the state of ports  1012  during a cleaning session, to provide to supervisors and/or others (including in reports of the cleaning process generated by the system) an indication of how the operation was carried out, for example, whether all of ports  1012  were used at some point, and for how long. Moreover, it is possible to provide through system  199  a defined sequence to be followed in cleaning a particular enclosure and to display prompts to an operative as to that sequence at block  208 . 
     To direct power to the sensors and LED banks  1018  and to allow transmission of their outputs to other parts of the system a connecting cable  1004  is provided that is secured (at  1006 ) by tape, suitable clips or the like to duct  1002 . Necessary electronics, signal conditioning for the sensors and power connections (not shown) are protected in a housing  1008  secured to panel  1024 , at which an end of cable  1004  terminates. Note that with suitable end fittings for outlet conduit  1002 , it is possible to run cable  1004  inside conduit  1002 , thus reducing the risk of damage to cable  1004 . 
     As an alternative to cable  1004 , it is possible to provide for signals from the sensors on cover  310   b  to be transmitted to the rest of the system by a short-range wireless connection for example using the “Bluetooth” or “Bluetooth Low Energy” or other suitable protocol. In this case, housing  1008  may contain a battery for supplying power to the sensors as required and to the LED banks  1018 . Note that as a further alternative, the functions of housing  1008 , pressure sensor  1022  may be provided in a housing secured temporarily or even permanently to the enclosure to be cleaned. 
     Note also that in embodiments where the pressure sensor for internal space pressure is to be located elsewhere in the system and connected to a tapping in a cover such as  310 ,  310   b  or  310   c , a flexible tube can be provided terminating at a tapping in the cover and secured along duct  1002  as shown in  FIG. 33 , although such embodiments are not preferred. 
     Outlet conduit  1002  (or other outlet conduits described herein) that correspond to outlet conduit  20  of  FIG. 2  are preferred to have smooth inner wall surfaces to avoid fouling with particulate material. Thus wire reinforced hose having a non-smooth inner surface is less preferred than hose with a smooth inner wall surface. 
     Exemplary Embodiment—Backpack 
     A prototype system  999  according to the invention has been developed and has proved satisfactory for cleaning electrical component cabinets on large surface mining haul trucks. The system uses a conventional reticulated workshop air supply as its gas source (item  32  of  FIG. 2 ) and the other components to the left of station “XX” in  FIG. 2  (excluding selector  50  which was not included) and were able to be accommodated in a suitcase-sized plastics casing  1030  suitable for carrying as a backpack or otherwise reasonably portable.  FIG. 34  is an elevation showing how the major components (only) of system  999  were able to be accommodated in the casing  1030 . Casing  1030  is shown without its lid, which is hinged at moulded fittings  1050 . Note that system  999  comprises casing  1030 , the equipment within it as shown in  FIG. 34 , a cleaning lance (for example lance  12  or one of the others lances  1160  or  2600  described herein), and all associated ducting. 
     A cyclone corresponding to cyclone  38  of  FIG. 2  is shown at  1036 , with its inlet for gas and particulates drawn from enclosures shown at  1034 . Item  1042  is a container inside which is a receptacle (not shown) for collection of particulates received from the cyclone at  1036 , the receptacle being emptiable when an ultrasonic transducer pair (sender and receiver, not shown) provides a signal indicating it is full. 
     At  1038  is a duct from the cyclone at  1036  leading to a cylindrical casing  1040  containing firstly a disposable paper bag-type filter (not shown in  FIG. 34 ) receiving gas and unremoved particulates from the duct at  1038 , and secondly a HEPA filter downstream of the paper-bag-type filter. At  1032  is a screw cap for accessing the interior of casing  1040  for removal and replacement of the paper-bag filter and removal and servicing of the HEPA filter. 
     The source of vacuum for drawing gas and particulates through the system is shown at  1044  (casing for a centrifugal or blower fan (not visible) and  1048  (motor for the fan). Gas leaves the system via a muffler  1046  via a port (not visible) at the left side of the casing  1030 . 
     Not shown in  FIG. 34  are triboelectric sensors for sensing particulate concentration at locations corresponding to stations F and K of  FIG. 2 . Electronics componentry (not shown) is housed in the lid (not shown) of the casing  1030 . Pressure transducers for locations corresponding to stations C, F, G, H and I of  FIG. 2  are mounted on a printed circuit board in the lid and connected to those locations by small-bore flexible plastics tubes. 
     Also housed in the lid is a relay-operated valve corresponding to item  52  of  FIG. 2  for controlling gas supply to the lance (not shown), and in particular shutting off that supply if pressure in the enclosure being cleaned rises to become too close to pressure in the surroundings (i.e. if there is a risk of loss of partial vacuum in the enclosure being cleaned). 
       FIG. 35  shows the casing  1030  in the same elevation as  FIG. 34  but now with screw cap  1032  removed and a filter bag holder  1052  removed from casing  1040  as is required for emptying. Bag holder  1052  (shown in  FIG. 36 ) comprises a plastics moulding in which vertical bars  1041  are arranged in a circle supported by circular parts  1057 . No filter bag is shown in  FIG. 36 , for clarity. As can be seen in the sectional view of  FIG. 37 , bars  1041  lie adjacent to the wall of casing  1040  when holder  1052  is placed in casing  1040 . Filter bag  1045  is held away from the wall of casing  1040  by bars  1041  when, in use, there is gas under pressure in bag  1045 . This ensures that between each pair of adjacent bars  1041  there is a space  1047  into which and down which gas passing through bag  1045  can pass as shown by arrows  1043 . Holding the bag away from casing  1040  in this way ensures that a large portion of the bag&#39;s surface is available for catching particulate material entrained in the gas in the bag  1045 . Item  1059  defines a space above the HEPA filter (not shown) so that its whole cross-sectional area is used. 
     The filter bag used in holder  1052  in the prototype is a commercially available porous paper filter bag having a circular opening. Gas and particulates enter the bag through a short duct  1051  that is separate from holder  1052  but is received therein as shown. A seal  1049  is provided on duct  1051  that when the bag is placed in holder  1052  seals against the inner wall of casing  1040 . 
     Additional Embodiments—Lighting 
       FIG. 38  shows a further cover assembly  310   d  that is similar in most respects to cover  310   c  and used in the same way. Items with numbers ending with “d” are the same as the corresponding items without the “d” as described above in relation to cover  310   b  as shown in  FIG. 33  and so need not be described again. (For example, item  1008   d  in  FIG. 38  corresponds in description and function to item  1008  of  FIG. 33 .) The difference between cover  310   b  and cover  310   d  is that lighting is provided in a different way. Associated with each port  1012   d  is a light source  1013   d  that, instead of providing diffused light as in the case of the LED banks  1018  of cover  310   b , project a thin sheet of light  1054  into an enclosure (not shown) on which cover  310   d  is used. (For clarity, such a sheet of light is shown only for one of the light sources  1013   d  in  FIG. 38 .) This is helpful to an operator in that particles in or passing through the light sheet  1054  are illuminated by the “Tyndall” effect and a user cleaning the enclosure has a clear indication of whether and where particles are still present in the enclosure and therefore need further attention. 
       FIG. 39  shows one way in which such a sheet of light can be produced. A miniature laser  1051  generates a narrow beam of light in the direction of an axis  1060  that passes through a transparent or translucent cylinder  1052  made of for example a suitable plastic material or even glass, the cylinder  1052  having a lengthwise axis  1053  perpendicular to axis  1060 . The effect of the cylinder  1052  is to convert the beam into a fan-shaped flat sheet of light  1054  in a plane perpendicular to the axis  1053 . 
       FIG. 40  shows this arrangement as realized in cover  310   d  for a typical port  1012   d . The panel  1024   d  of cover  310   d  comprises two layers secured together—one is a sheet  1055   d  of a suitably stiff plastics material and the other, on an outer face of panel  1024   d , is a sheet  1056   d  of a vacuum-formable transparent plastics material in which holes corresponding to ports  1012   d  are provided and in which are formed elongate dimples  1057 , one for each laser  1051 . Cylinder  1052  and laser  1051  are positioned within dimple  1057  between sheet  1056   d  and sheet  1055   d  in the desired orientation. In some embodiments, sheet  1055   d  is recessed as shown at  1061 . Electrical connections supplying power for the laser  1051  (not shown in  FIG. 38 or 40 ) may be run between sheets  1055   d  and sheet  1056   d  to a suitable termination (not shown) and may be flat copper strips, for example. The orientation of axis  1053  is vertical when the cover assembly  310   d  is oriented as shown in  FIG. 38 , so that a horizontal sheet of light  1054  is provided, as shown in  FIGS. 38 and 40 , although other orientations may be chosen. It will be recognized that other, different ways may be chosen to realize the described arrangement of laser  1051  and cylinder  1052 . (For example, not shown, panel  1024   d  may comprise only a single sheet such as sheet  1055   d , with laser  1051  and cylinder  1052  being accommodated in a short length of tube secured by gluing or otherwise, to panel  1024   d  at one end and closed at the other end.) Also, instead of a cylinder  1052 , a suitably shaped lens (not shown) may be used. 
     An embodiment with a further, optional enhancement is now described.  FIG. 40  also shows a light emitting diode (LED)  1058  optionally accommodated in dimple  1057  and oriented facing away from the sheet of light  1054  so as to be visible to a user. LED  1058  is arranged to be lit with power provided by the system in a colour that is modulated (by the processor shown in  FIG. 3  at  200 ) according to the measured concentration of particulates at the enclosure outlet  102   d  when its associated port  1012   d  was last detected (by the means described earlier above) as being in use—for example green in the event of a negligible concentration and red in the case of a heavy concentration. A user seeing that the LED  1058  for a particular port  1012   d  is showing red knows to take cleaning action at that port until the LED  1058  turns green, due to the particulate concentration at outlet  1020   d  falling. When the LEDs for every port  1012   d  are green and the measured concentration of particulates at outlet  1020   d  is adequately low, and the light from each light sheet  1054  does not show particles, the user has some assurance that cleaning is complete. As for lasers  1051 , conductors (not shown) providing power for the optional LEDs can be run between sheets  1055   d  and  1056   d  to suitable terminations for onward connection to the system. In some embodiments power for the LEDs is provided by the same power supply that supplies power to the instrumentation and control system shown in  FIG. 3 . 
     Although cover  310   d  is shown to have one light source  1013   d  associated with each port  1012   d , it is possible to provide them in other, or additional, positions. 
     In some embodiments, it is possible to make cylinder  1052  rotatable by a user so that the sheet of light  1054  can have any of a range of orientations. This can be achieved for example by securing a ferromagnetic element (not shown, for example a small disc) to cylinder  1052  and providing a magnet outside dimple  1057  to act on the ferromagnetic element to rotate the cylinder  1052 . 
     In other embodiments, the colour of the light from the laser is made adjustable by the user to enable a most suitable colour to be chosen. 
     Note that cover assemblies as described herein may comprise lighting as described herein, even where a cleaning lance such as lance  1160  with its own lighting is to be used. 
     Additional Embodiments—Workspace Environment Instrumentation 
       FIG. 41  shows an extended version  1075  of the instrumentation and data processing arrangement shown in  FIG. 3  and is representative of the instrumentation system of system  999 . Items having the suffix “b” in  FIG. 41  directly correspond to items with the same item number but no “b” suffix and so need not be described again, except to the extent that the extended arrangement of  FIG. 41  alters them. Thus, for example display  208   b  essentially is as described above for display  208 . 
     Instrumentation and data processing system  1075  has provision for two groups of sensors, the first being equipment sensors  202   b  that sense operating parameters as described above. 
     The second set of sensors  1070  comprises one or more sensors (not individually shown) for sensing parameters that relate to the condition of the workspace in which a user of the system shown in  FIG. 2  works and/or to the condition of the user him- or herself. For example, workspace-related sensors include in some embodiments an air quality sensor, such as a particulate level sensor or a temperature sensor. User-related sensors may include for example a temperature sensor that directly senses temperature inside an item of protective clothing. 
     The significance of workplace- and user-related sensors is that it is important in industry today to ensure that working conditions are reasonable and can be proven to be so, particularly where substances that are inherently toxic or harmful in certain concentrations or particle sizes are being dealt with. A further issue may be pollution by harmful substances. Therefore, system  1075  in some embodiments provides for sensing, recording (at item  211   b ) and transmission (at  213   b ) of data on workplace- and user-related parameters alongside equipment-related parameters. Further, system  1075  provides for the alarm, control and display functions  210   b ,  207   b  and  208   b  to reflect the importance of workspace and user-related parameters. 
     In some embodiments, item  1070  includes a particulate sensor (not shown) located in a workspace of a user but away from Station K, the blower  46  outlet ( FIG. 2 ). 
     This particulate sensor senses particulate levels independently of the system shown in  FIG. 2 . As an example, a suitable sensor for some applications could be an HPM-Series laser particulate sensor available from Honeywell, Inc. This has its own fan for continuous sampling of air and sensing of particulate levels using a laser light scattering method to detect and count particles in the sampled air flow. In some embodiments, the sensor is powered from the same power supply as that used by the other items in system  1075  (at block  1072 ). The sensor may be connected to data processing unit  200   b  (at block  204   b ) either by cable or wirelessly using any suitable protocol. 
     The sensed particulate levels in some embodiments are recorded alongside equipment-related quantities such as particulate concentration at Station F ( FIG. 2 ), so that a record is obtained of the particulate levels experienced by the user during a cleaning operation. 
     Further, data processing unit  200   b  may provide for alarms to be made drawing the user&#39;s attention to particulate levels in his or her workspace that are becoming excessive, display of the workspace particulate level, and, if particulate levels rise to a predetermined unsafe level actual shutdown of the equipment via control outputs (block  207   b ). 
     As described herein the system shown in  FIG. 2  may be operated to achieve cleaning of an enclosed space by either blowing gas into, and sucking it out of, the enclosed space or simply extraction by suction alone. In either case sensing of workspace- and user-related quantities may be used. 
     Additional Embodiments—Flexible Cover Assemblies 
     The cover assemblies  310 ,  310   a ,  310   b ,  310   c ,  310   d  described above are rigid or substantially rigid. However, it is possible to provide cover assembles that are formed using flexible materials. Such cover assembles can offer the advantage of being easier to store, when not in use, and easier to transport to and from a worksite. Further, an advantage may be avoidance of danger from breakage. Acrylic sheet such as that sold under such trade names as “Plexiglass” or “Perspex” may break under stress, with broken pieces potentially causing injury. 
     As an example of a suitable material for cover assemblies that are flexible, PVC material is available in the form of sheets that are transparent and flexible, being supplied in rolls. Note that the word “transparent” is here not intended to necessarily imply the degree of transparency of a pane of glass, but rather to imply sufficient transparency that a user of the invention can see inside an enclosure being cleaned sufficiently well to be able to assess the progress of cleaning and manipulate a cleaning lance (such as lance  12 ) adequately. 
       FIG. 42  shows a cover assembly  1100  formed in part from a sheet  1102  of flexible transparent plastics sheet material such as a suitable PVC material, positioned for fitment against an opening  1104  of an enclosure  1106  of ferromagnetic material whose interior is to be cleaned according to the invention. Cover assembly  1100  is shaped and sized to be able to abut a peripheral flange  1108  of enclosure  1106  and to span and close off the opening  1104  defined by flange  1108 . This is indicated in  FIG. 42  by the chain-dotted lines  1110 . Cover assembly  1100  has covers  1112  (described below) for ports  1114  allowing insertion of a cleaning lance (such as lance  12  or the lance  1160  described below) and an outlet port assembly  1116  for connection of an outlet duct (not shown) for removal of the cleaning gas and entrained particulate matter. 
       FIG. 43  is a cross-sectional view of a portion of cover assembly  1100  taken at station “AX-AX” showing two only of the ports  1114 , with one of them  1114   a  shown in use for insertion of a cleaning lance such as lance  12 . To secure cover assembly  1100  against gas leakage around its edge, cover assembly  1100  is provided with a flexible magnetic strip  1118  around its periphery that holds cover assembly  1100  against flange  1108  of the enclosure  1106 . Magnetic strip  1118  and the sheet  1102  are held together by a double-sided adhesive tape  1120  having a plastics foam between its two faces (as known in the adhesive tape art), also extending peripherally around the sheet  1102 . Tape  1118  and magnetic strip  1120  are shown in  FIG. 42  by dotted lines  1122 . Note that if required, cover assembly  1100  can be secured in place more reliably by the use of suitable adhesive tape (for example so-called duct tape) if required. 
     With a suitable choice of magnetic strip  1118 , cover assembly  1100  has been found practicable in many applications because the necessary difference between pressures inside and outside the enclosure  1106  can be not large enough for cover assembly to be sucked off flange  1108  and into enclosure  1106 . 
     The outlet port assembly  1116  is secured gas-sealingly to sheet  1102  by a suitable adhesive or by heat or solvent welding and/or by stapling or stitching. 
       FIG. 44  shows two only of the ports  1114 ,  1144   a  and associated port covers  1112 ,  1112   a  of two different types. Ports  1114 ,  1114   a  comprise slits formed in the sheet  1102  and preferably provided with holes  1124  at each end to prevent tearing of sheet  1102 . To limit flow of cleaning gas through ports  1114  when they are not in use, flexible port covers  1112  are provided that when their associated ports  1114  are not in use abut sheet  1102 . Chain dotted lines in  FIG. 44  show the positions of covers  1112 ,  1112   a  when they abut sheet  1102 . Covers  1112  and  1112   a  can be swung aside as shown for insertion of a cleaning lance such as  12  or  1160 . This can be done in two ways. Cover  1112  is secured to sheet  1102  along a vertical edge  1126  and cover  1112   a  is secured to sheet  1102  along a horizontal (as drawn) edge  1126   a . The covers  1112 ,  1112   a  may optionally be of the same type of material as the sheet  1102  and secured thereto by adhesive, solvent welding stitching or any other suitable method. As desired, the covers  1112  of cover assembly  1100  may be all of the type shown as  1112 , all of the type shown as  1112   a , or a mixture of both. 
     However, it has been found that in many applications pressure differences between an internal space being cleaned and the workspace outside are and can be maintained small enough that there is no significant leakage of particulate material through ports such as  1114  and  1114   a  even if the flaps  1112  and  1112   a  are omitted altogether. Accordingly, any of the flexible covers described in this specification may for suitable applications be provided with ports for cleaning lance insertion that comprise simply a slit (such as  1114  or  1114   a ) with anti-tearing holes at each end (such as the holes  1124 ). It is preferred that where such ports are provided, the slit extends in at least approximately an upright direction in covers intended to be used on vertical openings. Such ports are particularly convenient where they can be used, as they do not hamper folding or rolling up of flexible cover assemblies when not in use. 
       FIG. 45  shows a further flexible enclosure cover assembly  1130  positioned (as indicated by chain-dotted lines  1136 ) ready to be secured over an opening  1132  of an enclosure  1134 . Cover assembly  1130  is the same as cover assembly  1100  as described above save for two modifications. Elements of cover assembly  1130  that are the same as corresponding ones of cover assembly  1100  are numbered the same as in  FIG. 42 , save for a suffix “a”. The first modification is that an elongate stiffener  1138  is secured to and extends across the outer side of the cover assembly  1130 , for example by adhesive or heat- or solvent-welding or retention in a pocket. The purpose of stiffener  1138  is to prevent that part of cover assembly  1130  that extends over the opening  1132  from deflecting excessively into enclosure  1134  due to the pressure difference maintained across the cover assembly  1130  in use. Only one stiffener  1138  is shown, but in other embodiments several are provided where required. 
     The second difference between cover assembly  1130  and cover assembly  1100  is that cover assembly  1130  has peripheral flaps  1140  that in use are wrapped around corner edges  1142  of a peripheral flange  1144  around opening  1132 . Gaps  1146  are left between flaps  1140  where necessary to clear obstacles such as hinges  1148 . Flaps  1140  may be of a different material from plastics sheet  1102   a , for example of a suitable textile material with or without a plastics or rubberlike coating, for ease of bending around corners  1142 , and need not be transparent. 
     The portion  1149  of cover  1130  that abuts flange  1144  may be provided with double-sided tape and magnetic strip as shown in  FIG. 43  for cover  1100  or with a suitable sealing material only. Magnetic strip or individual magnets are provided at  1150  on flaps  1140 . Cover  1130  can provide a more secure connection to an enclosure (such as  1106  or  1134 ) than cover  1100 . 
     Both covers  1100  and  1130  can be rolled up for convenient storage and transport, due to the use of flexible material in their construction. 
     In other embodiments, flexible cover assemblies (not shown) can be provided with both stiffener(s) such as  1138  and flaps such as  1140  or only one of those features, as required. 
     A possible difficulty associated with flexible cover assemblies  1100  and  1130  is illustrated by the presence of outlet port assemblies  1116  (in cover assembly  1100 ) and  1116   a  (in cover assembly  1130 ). When ducts are connected to components,  1116  and  1116   a , they place stress on them which may significantly deflect the surrounding flexible material ( 1102  or  1102   a  respectively). This can risk separation of the cover assembly from the structure whose internal space is to be cleaned of particulates, and associated leakage of particulate material. 
     One solution is shown in  FIG. 62 . A plate  2700  of steel having a duct connection  2702  is secured to a structure  2704  whose interior is to be cleaned of particulates in a suitable position for connection of the duct (not shown) to connection  2704 . This may be done using any suitable form of fasteners, such as spring pins  2706  or screws (not shown) in holes provided in structure  2704  for the purpose or even by strong magnets. The flexible cover assembly (not shown) is then secured to plate  2700  by its magnetic tape as previously described. Thus, stress on the flexible cover assembly due to the duct connection is avoided. 
     Chain dotted outline  2708  shows one possible location for the magnetic tape to contact plate  2700 . However, the flexible cover assembly could extend to outer edges  2710  and  2712  of plate  2700  and be provided with cutouts to clear connection  2702  and fasteners  2706 , which would provide even more security against separation of the flexible cover from structure  2704 . 
       FIGS. 65 and 66  show yet another cover assembly  3000  for closing an opening in a container and for use in practice of the invention. Cover assembly  3000  is adapted to be placed against a surface surrounding an opening in a container to be cleaned, such as for example the cabinet  300  shown in  FIG. 16 , which has an opening  306  into an internal space  302 , the opening surrounded by a flange  304 . Such a container will be used here as one example for purposes of explaining cover assembly  3000 . 
     Cover assembly comprises a sheet  3002  of a flexible material that is translucent or (preferably) transparent and flexible, such as certain types of PVC. Secured to the edges of sheet  3002  around its periphery (and facing the inner side of cover  3000 ) are flexible magnetic strips  3004 , which in use of cover assembly  3000  hold sheet  3002  against flange  304 . An elongate element  3005  is secured along a top edge of sheet  3002  and is adapted to hook over an upper portion of flange  304 , for additional support of the weight of cover assembly  3000 , both in use and when it is being positioned on flange  304  for use. 
       FIG. 67  is a partial cross-sectional view on a plane normal to sheet  3002  at location “Z” on cover assembly  3000 , shown in position on flange  304 , and shows that the magnetic strip is secured to sheet  3002  by double sided adhesive tape  3006 . Suitable tapes for use with flexible transparent PVC sheet can be selected from among a range of tapes available from the Industrial Adhesives and Tapes Division of 3M (3M Center, St Paul, Minn. 55144-1000, USA), and are characterized in that they resist migration of plasticizer from the PVC into the adhesive, leading to weakening of bond strength. Transfer Tape 3M transfer tape F9465PC is one example of this class of tape. The same arrangement as in  FIG. 67  is used at each end of each of battens  3008 . 
     To limit bulging of sheet  3002  into opening  306  in use, cover assembly  3000  is stiffened by battens  3008  extending parallel to each other and to element  3005 . Battens  3008  are preferably made of a plastics material of suitably less flexibility than sheet  3002 . For example, in many industrial applications, battens  3008  may be made of the plastic or glass-reinforced plastic used in battens for stiffening sails of small sailboats. Battens  3008  can also be secured to sheet  3002  using double sided tape  3007  of suitable type, from the class mentioned above, although other suitable methods of securing may be used if required. 
       FIG. 66  is a horizontal cross-sectional view of the cover assembly  3000  in position ready to be moved in the direction of arrow “Q” to close opening  306  of cabinet  300 . 
     A modified cover assembly  3000   a  can provide extra security of positioning and retention on flange  304 . Cover assembly  3000   a  is identical to cover assembly  3000  except that battens  3008  are replaced by battens  3008   a  the same as battens  3008  but with ends adapted to hook onto flange  304 .  FIG. 68  shows one end of a batten  3008   a  of which each end has a hook  3010 . If, at each end of batten  3008   a , the dimension marked “FH” in  FIG. 68 ) of each hook  3010  is not more than about half of the flange  304  dimension marked “FF”, it is found that with some sideways movements and/or a little bending of battens  3008   a  both hooks  3010  can be made to hook over the flange  304  on opposite sides of opening  306 . 
     As an alternative to the arrangement shown in  FIG. 68 , one or both hooks  3010  of batten  3008   a  can be replaced by a slidingly movable hook  3012  as shown in  FIG. 69 . A spring  3014  is attached at one end to an anchor  3016  on a batten  3008   b , otherwise similar to battens  3008  or  3008   a , and at its other end to hook  3012 . Spring  3014  holds hook  3012  in position on flange  304  as shown in  FIG. 69  but allows hook  3012  to be moved sideways in the direction shown by arrow  3015 , for convenience during installation on the cabinet  300 . 
     Cover assembly  3000  (or versions with the any of the hooking arrangements mentioned above) is provided with a hole  3018  to which can be secured a rigid ferromagnetic plate  3020  having an exhaust duct  3022  thereon. Plate  3020  is formed on one edge  3024  to be able to hook over one of the battens  3008  (or  3008   a  or  3008   b  as applicable) which is taped to sheet  3002  only over part of the batten&#39;s width along a portion  3026  of its length. Magnetic strips  3028  are secured by double sided adhesive tape along sides of hole  3018  to hold plate  3020  onto sheet  30012  in use. 
     Ports  3028  for cleaning lance insertion are provided on cover assembly. These are shown as being of the type described elsewhere herein as having an elongate slit with anti-tearing holes at each end. However, it is to be understood that other suitable ones of the various port arrangements for flexible cover assemblies described herein may also be used instead if desired. 
     Cover assembly  3000  and its described variants are convenient to use and to store, as they can be folded or even rolled up, for easy carrying and storage after use. 
     A further feature of cover assembly  3000  and its described variants is that lighting of the space being covered can be provided by installing one or more LEDs or other lighting devices in the battens  3008 , or  3008   a  or  3008   b .  FIG. 70  shows a cross-section of a portion of cover  3000  at a batten  3008  provided with a recess  3009  in the batten  3008  for an LED  3032 . Double sided tape  3034  has a hole  3011  near the recess  3030  to allow light from LED  3032  to pass through sheet  3002 . The forms and refinements of lighting referred to in this specification by reference to  FIGS. 38-40  may optionally be applied to lighting provided in this manner if required, the battens such as  3008 ,  3008   a ,  3008   b  in effect providing support for their elements in the same way that non-flexible cover assemblies of  FIGS. 38-40  do. 
     Further flexible cover assemblies are described below by reference to  FIGS. 49 to 55 . 
     Additional Embodiments—Cleaning Lances 
     There will now be described further embodiments of cleaning lances that are alternatives to cleaning lance  12 . 
     In some embodiments, a cleaning lance with more functionality than cleaning lance  12  may be provided.  FIG. 46  shows a cleaning lance  1160  with additional functionality and features. In addition to providing an outlet for a jet of cleaning gas (for example air) cleaning lance  1160  has the following additional functions:
         1. Provision of lighting inside an enclosure being cleaned using lance  1160  rather than or additional to lighting comprised in a cover assembly;   2. Provision of an inlet port for air to be sampled for the presence of particulate matter in the workspace where the lance  1160  is in use, but outside the enclosure being cleaned;   3. Provision of sensor(s) for continuous determination of a difference in pressure between the work area outside, and the interior of, the enclosure being cleaned using lance  1160 ;   4. Provision for sensing which of the available port assemblies is in use at a given time (i.e. which port assembly has cleaning lance  1160  inserted into it); and   5. Provision of alarms well-located to warn a user of a system condition or malfunction.       

     While items 1 and 3 may be provided in the enclosure cover being used (as described above in relation to covers  310 ,  310   a ,  310   b ,  310   c  for example) their incorporation in lance  1160  instead can simplify the design of enclosure covers with which it is used. This is particularly advantageous in the case of the flexible enclosure covers (including  1100  and  1130 ) as described above. 
     While lance  1160  as described below incorporates all of the items 1 to 5, it is possible and within the scope of the invention to provide embodiments that are lances (not shown) comprising or adapted to provide only one or more of them. 
     Lance  1160  comprises a duct  1162  for direction of cleaning gas (eg air) from an inlet hose  1164  to an outlet  1166  that in use of lance  1160  is positioned within an enclosure being cleaned in the same way as described above in relation to lance  12 . A valve (not shown) controlled by a movable element on a handle assembly  1168  such as a trigger  1170  is provided to enable control of gas supply. 
     A rounded formation  1172  is secured on duct  1162  adjacent to outlet  1166  and is sufficiently soft and resilient to reduce any tendency of the outlet end of lance  1160  to damage componentry in an enclosure being cleaned. (This feature could optionally also be incorporated in lance  12 .) Formation  1172  may be formed from a suitable resilient plastic or rubber or rubberlike material, for example. 
     Also secured on duct  1162  is a rounded formation (called herein an “olive”)  1174  that contains, in a portion having a clear plastics cover  1176 , lighting elements  1178  positioned to provide light close to the area in which the outlet  1166  is positioned. Olive  1174  is so positioned along duct  1162  as to be, in use, within the enclosure being cleaned. Lighting elements  1178  in some embodiments are light emitting diodes (LEDs). Optionally, as best seen in  FIG. 47 , additional lighting elements  1180  comprise lenses that in the same way as discussed by reference to  FIG. 39  provide lighting only in flat “sheets”, to help a user assess visually the quantity of particulates present near outlet  1166  using the Tyndall effect. Switches  1182  (or a multi-position switch, not shown) on handle assembly  1168  can enable a user to switch between lighting elements  1180  and lighting elements  1178  as required. 
     Cleaning lance  1160  further comprises sensor(s) (not shown) for sensing the pressure difference between the interior of the enclosure being cleaned and its exterior, i.e the workspace. This quantity is important because if the interior is not held at a pressure sufficiently lower than the exterior uncontrolled leakage of particulates may result. In one embodiment ports  1190  and  1192 , respectively at the handle assembly  1168  and olive  1174 , are provided and in fluid communication with a differential pressure sensor (not shown) within handle assembly  1168  or olive  1174  for sensing the pressure difference. In another embodiment, separate absolute pressure sensors are provided, one connected to port  1190  and the other connected to port  1192 . 
     For sensing of particulate concentration where a user is working, the lance  1160  is provided with a port  1184  for sampling the atmosphere at the end of lance  1160  opposite outlet  1166 , i.e. outside the enclosure being cleaned. A duct  1188  is provided from port  1184  through which air is drawn from the workspace through a particulate concentration sensor (not shown).  FIG. 48  shows schematically a system  30   a  that is a modified version of the system  30  ( FIG. 2 ), the modification being inclusion of duct  1188  connecting port  1184  to the inlet of cyclone  38   a  so that workspace air is sucked through port  1184  and that air&#39;s particulate concentration sensed by a suitable sensor (not shown) at a station “N”. Duct  1188  is shown in  FIG. 48  as joining the stream of cleaning gas and entrained particulates from duct  20   a  or duct  48   a  upstream of station “F” but may instead be downstream of station “F”. Station “N” and the workspace particulate concentration sensor may be within in an enclosure containing some or all of the components shown to the left of the chain-dotted line in  FIG. 48 . 
     The particulate concentration at the lance  1160  is thus sensed along with the other sensed quantities mentioned above, and may be logged along with those quantities. (In  FIG. 48 , to avoid repetition of the description of system  30 , components having corresponding functions to components of system  30  are for simplicity numbered the same as those components of system  30 .) Station “T” in  FIG. 48  is where the pressure difference between the interior of the enclosure being cleaned and the surrounding workspace is sensed. (In embodiments where the function of measuring pressure difference is not included in lance  1160 , it can be sensed by a differential pressure sensor having ports inside and outside the enclosure being cleaned, for example at a location such as station “C” in  FIG. 2 .) 
     In an alternative cleaning lance embodiment (not shown), a particulate concentration sensor (not shown) may instead be provided directly on lance  1160 , for example in handle assembly  1168 . Duct  1188  is then not required. 
     In other alternative embodiments (not shown), particulate concentration sensing in the user workspace is not incorporated in the cleaning lance but provided by a sensor (not shown) simply placed at a suitable location in the workspace. Where an enclosure is provided (for example a backpack) for major components such as blower  46  or  46   a , cyclone  38  or  38   a  for example, the workspace particulate concentration sensor may be located in that enclosure with an inlet port on the exterior of the enclosure. Duct  1188  is then not required. 
     Warning lights  1194 ,  1196  are provided on handle assembly  1168  (i.e. at positions outside the enclosure being cleaned) where they are difficult not to notice. These can warn of malfunctions or indicate the status of other quantities. In one embodiment, lights  1194  and  1196  warn respectively of (a) an inadequate pressure differential between the interior of the enclosure being cleaned and the atmosphere in the workspace and (b) any one of the other sensed quantities being outside specified limits—for example, a full load of collected particulate matter (for example in container  1042 ) sensed at Station “L” in system  30   a , or excessive particulate concentration in the workspace (as sensed at Station “N”). Lights  1194 ,  1196  are shown on one side of handle assembly  1168  but may be provided on both sides thereof for convenience of users who may be either left- or right-handed. The warning lights  1194 ,  1196  are driven by the data processor (See block  200   b ,  FIG. 41 ) via the “alarm” outputs (block  210   b ). 
     Cleaning lance  1160  may be used with enclosure covers that do not have the feature, mentioned above, of sensors that identify which port assembly is in use. Cleaning lance  1160  may optionally include means for doing this. This can be explained using cover assembly  1100  as an example. It is possible to provide, adjacent to each cover port or port assembly, a passive RFID (Radio Frequency Identification) or passive NFC (Near Field Communication) tag identifying the particular port or port assembly, and to provide in olive  1174  or handle assembly  1168  a reader (not shown) for the tags. Thus, passive NFC tags  1200  are shown near port covers  1112  on cover assembly  1100 . NFC-type technology is the preferred form of RFID because of its short range. As the lance  1160  is inserted into a port  1114 , or as it is withdrawn, the reader can sense (read) the particular tag associated with that port and identify it to the data processor  200   b . This may be logged along with the various sensed quantities, so that when a record of a period of cleaning is examined, it can be verified, for example, that every port was used. In other embodiments a tag may be provided adjacent each port or port assembly that bears a visual symbol such as a linear-type or circular barcode or QR code, and a suitable reader may be provided in olive  1174  or handle assembly  1168 , again to identify the port in use. A circular barcode may be used. Being able to avoid provision on an enclosure cover of port-identifying sensors is convenient in the case of flexible enclosure covers such as  1100 ,  1130 . 
     To enhance the reliability of port identification, lance  1160  may be provided with multiple NFC tag readers spaced along its length. For example, in addition to a reader in olive  1174 , there may be another reader in the formation  1172 . As lance  1160  is entered into a port with an associated passive NFC tag, the reader in formation  1172  first detects the tag, and as olive  1174  passes inwardly through the port, its reader detects the tag. The reverse occurs as lance  1160  is withdrawn from the port. Thus, two readers detect the tag, and the order in which they are detected allows both insertion and withdrawal to be distinguished. 
     In some embodiments, the gas supply valve (for example valve  32   a  of system  30   a ) is prevented by the data processor  200   b  from allowing cleaning gas to flow to the lance  1160  if sensors or readers comprised in the enclosure cover (as previously described) or comprised in lance  1160  do not indicate that a port has been opened (and, if the refinement of the previous paragraph is included, that lance  1160  has been inserted). This avoids the potential safety hazard of escape of cleaning gas outside the enclosure being cleaned. 
     Wiring (not shown) for lighting elements  1178  and  1180 , and in applicable embodiments for any pressure sensor or tag reader comprised in olive  1174 , and a small-bore tube in embodiments where port  1192  in olive  1174  is connected to a pressure sensor in handle assembly  1168 , extends in a conduit  1202  from olive  1174  to handle  1168 . 
     Between lance  1160  and the remainder of the system  30   a , there extends the hose  1164  for cleaning gas, wiring for lighting elements  1178 ,  1180  and sensors or readers (not shown) in cleaning lance  1160 , and in applicable embodiments duct  1188 . These may be held together for at least part of their length or contained in a single flexible conduit, for safety and convenience of use. 
     Still other possible features may be provided a cleaning lance. Thus,  FIG. 61  shows another cleaning lance  2600  that is an alternative to lances  12  and  1160 . Lance  2600  has a duct  2602  for directing gas into an enclosed space to be cleaned and a handle assembly  2604  for manipulation of lance  2600  by a user. Lance  2600  has an “olive”  2612  essentially the same as olive  1174  of lance  1160 , except as described below. (Lance  2600  does not have a formation corresponding to formation  1172  of lance  1160 , but may be provided with one if required.) 
     Lance  2600  has the same sensing capabilities as described above for lance  1160 , namely sensing:
         pressure difference between the portion (eg olive  2612 ) inside the space being cleaned;   particulate concentration in the workspace (more particularly at the lance  2600  itself);   whether a port assembly is in use and if so, which one, using for example an on-lance barcode or other optical reader or an NFC or other reader.       

     There may also be provided a GPS capability on the lance  2600 . Location of the lance is a useful quantity to record as a part of the process of independently verifying cleaning work, but also for other purposes as set out below. 
     Lance  2600 , instead of a wired connection to other parts of the system in which it is comprised (as in lance  1160 ) communicates through a wireless link using a suitable digital protocol such as Bluetooth, Bluetooth Low Energy or even (where longer range is required) the LORA protocol. Power is provided by a rechargeable battery  2626 , for example a Lithium-Ion type. By this means sensor data from lance  2600  is sent to the data processing system (eg system  1075  of  FIG. 41 ) and alarms, warnings and desired computed sensor outputs are sent back to the lance  2600 . 
     A digital alphanumeric screen  2614  is provided on lance  2600  for display of warning and alarm information and of sensor outputs. This includes in particular at least the key quantities required by a user during the cleaning operation. In particular, screen  2614  may display particulate concentration from the workspace particulate concentration sensor so that the user can monitor it for his or her own safety, and the concentration of particulate matter in air leaving the space being cleaned, a key parameter in establishing successful completion of cleaning. The electronics associated with receiving data for display and driving the screen are also energized by the battery. 
     Screen  2614  may be for example of LED, OLED, LCD or so called “e-ink” type, the latter providing good visibility in high ambient light conditions. 
     Screen  2614  may be touch sensitive so that selection of options (see discussion of options below) can be by touching the screen  2614 . Alternatively, a separate control  2616  may be provided. 
     The following are additional features that make lance  2600  differ from lances  12  and  1160 , and the reasons for them. 
     Pulsating Flow Capability 
     Control of gas flow through (and from) the cleaning lance (eg  12  or  1160 ) by means of a user-operable valve on the lance itself (for example item  16  on lance  12  or  1170  on lance  1160 ) and a gas supply control valve (eg  52 ,  52   a ) provides “on/off” control and steady or slowly variable flow when gas is flowing. However, lance  2600  is adapted to make gas stream  2606  pulsating, either at all times when that gas stream is turned “on” (by trigger  2608 ) or when the user makes a deliberate selection of pulsating flow instead of steady flow. Gas is supplied to lance  2600  through flexible hose  2610 .) Pulsating flow in duct  2602  can be provided by a solenoid-operated valve member (not shown) within the lance  2600  with time-varying current being supplied to the solenoid. When non-pulsating flow is required, the solenoid is caused to move the valve member to a position in which gas flows directly and without interruption from hose  2610  to duct  2602 . In an alternative way of providing pulsating flow, energy in the gas supply itself can be used to move a valve member (not shown) cyclically, by use of the principle of a pneumatic hammer or riveter, as known in the art. Providing pulsating flow either at all times or when selected has several advantages. One is the potential for more effective cleaning in at least some circumstances, and the other is the potential for reduced cleaning gas flow. In some embodiments and applications, the latter advantage means that an adequate cleaning gas supply for some tasks may practicably be provided by a simple pressure vessel (eg a lightweight carbon-fibre reinforced plastics pressure vessel. Where a solenoid-operated valve is used to provide pulsating flow, the solenoid can be operated from the battery located at  2626 . 
     “Before and After” Image Capturing Capability 
     The availability of very small video cameras based on charge-coupled devices (CCDs), as known for example in the mobile telephone art, enables a further enhancement of the cleaning lance. Lance  2600  is provided not only with lighting that is close to the point where cleaning is actually taking place, as described above in relation to olive  1174  of lance  1160 , but with a video camera (not shown) located for example within the olive  2612 . Such a camera can be controlled by the system  1075  to take “before and after” images of an area being cleaned when there is detection (by the NFC method or barcode reading as described above) of lance  1160  being entered into a new port assembly and being withdrawn, the images being stored along with sensor data to further enhance verification that cleaning has been adequate. 
     Lighting 
     Where lance  1160  provides for two types of lighting within olive  1174 , lance  2600  further enables adjustment by a user of the intensity and/or the colour of the lighting provided. It is found that visibility in a dusty environment can sometimes be enhanced by varying these quantities. 
     Multiple Alarm/Warning Methods 
     Instead of or in addition to the warning lights  1194 ,  1196  of lance  1160 , cleaning lance  1160  may be enabled to provide warning or alarm signals to a user by provision of onboard sound transducer(s) (not shown) for example of piezoelectric type, and/or handle vibration transducer(s)  2614  so that a user is unlikely to fail to notice such conditions. Further, an LED, OLED or LCD (or other digitally operated) screen may be provided on the lance itself to display nominated sensed values, for example particle concentration outside the space being cleaned and at the lance. 
     Particulate Sampling at the Lance 
     Lance  2600  may be provided with a particulate sampling capability in the same way as described above in relation to lance  1160  (using a sensor remote from lance  1160  and a sampling tube  1188 ) or alternatively, a particulate concentration sensor may be provided on lance  2600  itself, also operated from the battery  2626 . It is not necessary that the on-lance particulate sensor be of the same type as the particulate concentration detectors. In fact, having readings from different types of sensors can be useful as they may be affected differently by particular environmental conditions, particulate size distributions and the like and any significant difference in readings can be a useful indicator of a need for investigation and or action. System  1075  can be adapted to flag such a situation with a warning or alarm. 
     A still further cleaning lance  3500  will now be described, by reference to  FIGS. 71, 72 and 73 . Lance  3500  includes certain additional differences from cleaning lance  1160  and  2600  shown in  FIGS. 46 and 47  and  FIG. 61  respectively. Cleaning lance  3500  has a main body  3512 , a handle  3513 , a trigger-type switch  3515  for control of cleaning gas flow, a detachable rechargeable battery pack  3517  for powering all its electronic and electric onboard functions, and a cleaning gas inlet hose connection  3519 . 
     Instead of the “olive”  1174  of lance  1160  (and  2612  of lance  2600 ) cleaning lance has a group of three separate conduits  3502 ,  3504  and  3506  that enter a space to be cleaned through a port such as port  1114  for example, these conduits being held closely adjacent to each other along their length, and there is no formation corresponding to formation  1172  of lance  1160 . The intent is to ensure that the cross-section of that portion  3501  of the lance  3500  that actually enters a space to be cleaned is of more nearly constant cross-section than olives  1174 ,  2612  and formation  1172  allow. It has been found that this is preferable where flexible cover assemblies such as cover assembly  300  for example, with slit-type ports such as ports  3028  are in use. Lance insertion and manipulation is easier and there is less chance of damage to such a cover assembly. 
     Duct  3502  is for the cleaning gas (eg air). Duct  3504  has at its free end a small digital video camera  3508  corresponding to the camera of lance  2600 . Duct  3506  has at its free end a light source such as an LED  3510 , to provide illumination of the area to which cleaning gas is being directed. Wiring to the camera  3508  and light source  3510  extends along ducts  3504  and  3506  back to main body  3512  of cleaning lance  3500 . Light source  3510  may be for example a “white” LED whose light colour is controllable, and the colour used may be made variable by a user to enhance the ease of recognition of dust for a particular application. 
     Instead of the alphanumeric screen  2614  of cleaning lance  2600  there is installed in main body  3512  a screen  3514  capable of showing video from the camera  3508 . Screen  3514  is able also to show alarm signals, and menus of available operational choices that a user may make. The system is adapted to enable not only the capture of “before and after” images of areas subject to cleaning (as in lance  2600 ) but to provide an aid for aiming and positioning the lance as required. Screen  3514  also of course is able to display all parameters able to be displayed by the scree  2614  of lance  2600 . 
     Simple pushbutton or other suitable controls  3516  are provided for selection of the various functions of the lance  3500  as required. 
     In addition to the potential to show alarm conditions on the screen  3514  a warning light  3518  is provided to alert a user to any condition requiring action. 
     Optionally, accelerometers and a GPS-based position-determining capability (not shown) may also be provided in the main body  3512  of cleaning lance  3500 . The intent is that accelerometers can detect large values consistent with dropping or abuse of the lance  3500  that risks damage and that the positioning capability allows location—and lack of movement—to be detected and logged. 
     The pulsating flow capability of lance  2600  is also provided via a valve (not shown, but preferably in main body  3512 ) controlled by (for example) a pulse-width modulated signal to turn flow off and on. The frequency and mark-space ration of valve operation may be made variable or selectable by a user to suit a particular application. 
     Also in common with lance  2600  is provision of one, and preferably two, airborne dust monitoring sensors (not shown, but having inlet ports  3520 ) for monitoring and logging of workspace air quality, and the provision of an alarm in the event of excessive dust in the workspace. Suitable gas detecting sensors include for example the laser-based type sold by Honeywell, including type HPMA11550-XXX. These are very small and have their own fan. Particulate capability as small as PM2.5 are available as is PM10 capability. The provision of two dust sensors provides reliable operation and some insurance against one of them losing correct calibration. 
     Excessive disagreement between their readings may itself be made an alarm condition. It is possible instead of two identical dust sensors to use two different types, so as to further enhance confidence in their readings. 
     Pressure sensors (not shown) may be provided in lance  3500 , as for lance  2600 . 
     A barcode or QR code reader  3522  is provided also, to identify both the equipment being cleaned and the particular port being used, from for example stickers applied to the particular cover assembly in use adjacent to their ports. Other port identifiers, readers and protocols may be used as desired, for example, such as NFC technology. 
     It is desirable to ensure that there is positive verification of actual insertion of the lance  3500  into all required ports, and to this end sensors are provided on lance portion  3501 . In one embodiment, a set of several miniature Hall Effect sensors are provided in a housing  3524  close-fittingly wrapped around the ducts  3502 ,  35104  and  3506 . These can be triggered (i.e. change state) as they pass small magnets (not shown, but which may be short lengths of magnetic strip) secured on the cover assembly in use closely adjacent to each port. These sensors are positioned at a range of positions along and (preferably also) around the lance portion  3501  so that their triggering can allow the instrumentation software (running in block  200   b  of  FIG. 41 ) to determine that insertion has happened, and when and, to a degree governed by the number of sensors, the extent or depth of insertion. 
     In some embodiments, Hall Effect sensors can be placed at a range of positions along ducts  3504  and/or  3506  provided the material of those ducts is chosen so as not to interfere with their operation. 
       FIG. 73  shows another arrangement for a portion  3530  of a lance (not shown, but otherwise functionally similar to lance portion  3501 ) that enters a space to be cleaned. Lance portion  3530  comprises a single duct  3531  that contains at its free end  3532  a camera  3534  and light source  3536  that do what camera  3508  and light source  3510  of lance  3500  do. A duct for cleaning gas runs inside duct  3531  and has an outlet  3538 . This arrangement can be more readily twisted about its own longitudinal axis than lance portion  3501  when in use. 
     It is to be understood that in the design of a system according to the invention, a selection of the various features described herein for lances  12 ,  1160 ,  2600  and  3500  can be made. Some features may be incorporated and some may not. Not all applications would for example require the comparative sophistication of cleaning lance  3500 . For example, although in some applications sensing the pressure differential between a space being cleaned and the workspace outside it is very important, in others, it can be quite unimportant, so that no sensor for the space being cleaned need be provided. 
     Application of Ventilation or Vacuum Cleaning Alone 
     It is to be noted that there are many applications in industry where extraction of air or gases, in each case with or without particulates, is achieved by mechanical suction means alone. Accordingly, a further inventive concept using a system as shown in  FIG. 3 or 41  above, is provision of a mechanical ventilation system where both equipment-related sensors and workspace- and/or user-related sensors are provided, and wherein signals from specific ones of the sensors (workplace-, user-, or equipment-related) are used to provide any or all of alarms (or warnings), display the parameter value(s) of concern and if desired or necessary shut down or otherwise control either the ventilation system or the equipment being ventilated. A very wide range of sensors is available today, for sensing not only of particulate levels, but also of potentially harmful gases (eg Hydrogen Sulphide) and suitable ones of these may be selected and used. 
     Some industrial processes require different levels of ventilation according to how a the process is being carried out or the stage it has reached, and it is desirable to be able to adjust ventilation to suit—either to provide adequate ventilation or to limit wastage of energy when a particular level of ventilation is not required. Therefore, instead of, or in addition to, alarms, warnings and shutdown commands, it is possible to provide for automatic control of the ventilation system to maintain effectiveness and save energy in a range of conditions. 
     The systems and embodiments described above amount to examples of the further inventive concept introduced in the previous paragraph. Further examples of potential application areas include grinding equipment and saws (eg for cutting stone kitchen benchtops, a known area of particulate problems). Both mobile and fixed types of equipment can provide other potential applications. 
     The apparatus and methods described herein may be adapted to removal of particulate matter from various entities, with various geometries. Referring to  FIG. 28 , (a) represents schematically applications of the type disclosed above, showing in section a cover  700  (corresponding to cover  310  for example) is fitted over an opening  702  of a cavity  704  in an object  706 . Item  708  is a cleaning lance (similar to lance  12 ), items  710  are ports (similar to ports  340 ), item  712  is an outlet duct (similar to duct  20 ), and item  714  is a seal (similar to seals  318  or  321 ). 
     Diagram (b) of  FIG. 28  represents schematically an application to removal of particulate matter from a surface  716 . Hood  718  (shown in section) is positioned to abut surface  716  with a seal  728  extending around the area of surface  716  covered by hood  718 . Cleaning lance  722  extends through one of several ports  720  in hood  718 .  726  is an enclosed space defined between surface  716  and hood  718 . An outlet duct  724  is provided for removal of gas and particulate matter. 
     Diagram (c) of  FIG. 28  represents schematically an application where an object  730  is to have particulate matter received and is covered for the purpose by a cover  734  that abuts a surface  732 . Cleaning lances  736  extend through ports  738  and are moved as required. Seal  740  limits or prevents leakage between cover  734  and surface  732 . 
     Although examples (a), (b) and (c) all show covers ( 700 ,  718 ,  734 ) that can abut a flat surface, this is not essential. Where an application requires it, the boundary between cover and the entity it abuts in use need not be planar. 
     Note also that the object  730  could be an object, or surface  732  could be a surface, on which some particulate-generating process is being carried out, for example sanding, grinding or “scabbling”. Although not shown, the apparatus and methods described may be adapted to contain, and enable removal of, particulates in such cases also, for example by providing an extra access port in the cover for equipment used in the process or for the arm of an operator reaching into the cover. 
     Covers according to the invention need not necessarily be shaped to cover a flat surface (such as a flange around an opening of an electrical cabinet). Covers for performing the invention (in the same way as covers  310 ,  310   a ,  310   b  and  310   c ) may be contoured to suit other enclosure geometries. For example, large electric motors (not shown) s may have openings for access to brushes and commutators, and these are components that may need to be cleaned. It is possible to make a cover similar for example to cover  310   b  ( FIG. 33 ) save that it is arcuately shaped to cover such an opening during cleaning. In this case, however, ports such as ports  1012  and port assemblies  340  are unsuitable. However, port assemblies of the type shown in  FIG. 4  can be used, with at least one slit disc (the same as disc  94 ) having its slit (corresponding to slit  96 ) parallel to the motor shaft. 
     Application to Cleaning of Sets of Electrical Machines 
     A particular example of an application where covers that do not seal against a flat surface will now be described. 
       FIG. 49  shows an arrangement  1401  (known as a motor-generator set or MG set) of electric machines that can present a cleaning problem. MG set  1401  comprises a synchronous AC electric motor  1403  that drives a number of DC generators  1405 ,  1406   1407  simultaneously, these and the motor  1403  having their shafts connected to each other in a chain-like manner to rotate as a unit. Bearing blocks  1409  are typically provided between adjacent pairs of the machines  1403 - 1407  in this arrangement and at the end-most generators  1405 . MG sets of this type can be found in some electric walking draglines, as found in surface coal mining operations, where the generators provide power to DC motors (not shown) that in turn drive bucket hoisting, bucket dragging and swinging functions of the draglines. Variation of the motors&#39; field strengths provides speed control for these functions. MG sets as described here are not found in all draglines but are still common.) 
     Cleaning of commutator/brush assemblies of the generators and of particulate matter that accumulates between and also within the individual machines  3 - 7  is generally time-consuming, hence expensive in terms of machine downtime, and can present difficulties through exposure of personnel to hazardous particulate matter. 
       FIG. 50  shows in a schematic manner how embodiments of the present invention may be applied to such cleaning. Spaces  1411  between each pair of machines  1403 - 1407 , are temporarily enclosed as described below, in part using cover assemblies described below. Also, spaces  1413  at the outer ends of the endmost generators  1405 , including in typical cases the outboard bearing blocks  1409  there, are enclosed, also as described below. The cover assembles for spaces  1411  and  1413  are shown in  FIG. 50  schematically only, by dotted lines. 
     During cleaning, some or all of spaces  1411  and  1413  are maintained at a pressure below atmospheric pressure by drawing gas (for example, air) out through ducts  1415  that carry air and particulate matter entrained in that gas. The particulate matter within each of spaces  1411  and  1413  is dislodged by blowing gas (for example air) into them using cleaning laces as described above, such as lance  12  or lance  1160 . In  FIG. 50 , ducts  1415  are shown as parts of a manifold  1417 , with an outlet  1471  to a system (not shown) such as has been described above by reference to  FIG. 2  or  FIG. 48 . However, individual spaces  1411  or  1413  may be ventilated individually or in smaller groups, in alternative embodiments. 
     Thus, it can be seen that the cleaning method is essentially as described earlier herein. This can extend further to direct vacuum cleaning of parts in spaces  1411 ,  1413  once gas drawn therefrom is found to have satisfactorily low particulate content. Instrumentation, control and cleaning gas supply arrangements may be in accord with any of the arrangements for these described for other embodiments above. 
     Note that when the spaces  1411  and  1413  are enclosed, they are connected to each other by the gaps between stators and armatures of the machines, and flow of air (or other gas) and entrained particulate matter through these gaps must be taken account of in the cleaning process. This is described below. 
       FIG. 51  shows a side view of a pair of generators  1406  and  1407  of MG Set  1401 , mounted (along with the other parts of the MG Set  1401 ) on bearers  1419 .  FIG. 52  shows the same components (and from the same viewpoint) as  FIG. 51 , with the space  1411  between generators  1406  and  1407  now closed in part by cover assembly  1421 .  FIG. 53  shows these components in section, at station “Q-Q” shown in  FIG. 52 . 
     Cover assembly  1421  is flexible and able to be draped over the two adjacent generators  1406  and  1407 , being temporarily secured to their casings  1423  and  1425 . 
     Cover assembly  1421  comprises a sheet  1427  of flexible airtight (or substantially airtight) material that is flexible to enable draping over generators  1406  and  1407  from above. To support sheet  1427  over the space  1411 , stiffening rods  1429  extending parallel to each other and generator shaft  1431 , are provided. These rods  1429  are received in longitudinal pockets formed on the sheet  1427 , as shown. (However, any suitable alternative arrangement for providing stiffening rods  1429  may be used, for example by use of a suitable adhesive to stick them to sheet  1427 .) The stiffening rods extend far enough longitudinally along sheet  1427  to in use bear directly or through their pockets  1433  and sheet  1427  on the casings  1423  and  1425  of generators  1406  and  1407 . Stiffening rods  1429  do not only support the weight of sheet  1427  but prevent excessive inward deflection of sheet  1427  due to the lower-than atmospheric pressure maintained in space  1411  in use. Cover assembly  1421  is provided with a fitting  1435  for its duct  1415  for removal of gas and particulate matter from space  14112 . 
     To hold cover assembly in place on casings  1423  and  1425 , pockets  1437  are formed along its end edges, these pockets  1437  containing continuous lengths of magnetic strip  1441  (or, not shown, magnetic strip segments or individual (for example “button”-shaped) magnets). Also provided adjacent to each pocket  1437  are suitable elongate flexible seals  1439 . 
     Similarly, pockets  1443  with magnets, or magnetic strip or magnetic strip segments therein and seals (not shown) similar to seals  1439  are formed along its longitudinal edges so that the cover assembly  1421  can be secured sealingly to the bearers (or other structure) on which generators  1406  and  1407  are mounted. 
     As an alternative or adjunct to the magnetic method of attachment described in the previous two paragraphs, adhesive tape may be used to secure cover  1421  to bearers  1419  and generator casings  1423  and  1425 . 
     Sheet  1427  is shown as formed from a sheet of flexible but transparent or translucent material such as PVC (as described above in relation to cover assembly  1130 ), so that a user can see what he or she is doing when cleaning space  1411 . However, alternatively, other materials may be used such as textile material with a elastomeric and gas-sealing coating as is known in the art. Where an alternative material is not transparent, window segments (not shown) of transparent material may be provided at suitable locations in sheet  1427  to allow space  1411  to be seen into. 
     The sheet  1427  is provided with multiple port covers  1445  in appropriate positions so that a cleaning lance  1447  can be inserted and used to dislodge particulate matter in space  1411 . Lance  1447  may be similar to (or the same as) lance  12  or lance  1160  described above, and connected to a system the same in its functionality as the system  30   a  ( FIG. 48 ). Lighting of space  1411  may be provided by lighting on a lance such as lance  1160  or on cover assembly  1421  itself in essentially any of the ways described above in relation to other cover assemblies. Similarly instrumentation may be provided in essentially the same ways as described above, including sensors (not shown) secured on cover assembly  1421  or on lance  1447  or both. 
     In  FIGS. 52 and 53  port covers  1445  of either of the types shown in  FIGS. 42-46  are shown. However, other port arrangements as described earlier above may be used if required. Those port arrangements which require a fixed portion (eg such as component  812 ) simply require that the fixed portion be secured to the flexible sheet  1427 . 
     Cover assembly  1421  has been described by reference to generators  1406  and  1407  but is equally applicable to any of the spaces  1411  shown in  FIG. 50 . Where a space  1411  adjacent to motor  1403  is to be covered, it may be necessary to provide a temporary or permanently attached flange (not shown) on motor  1403  to enable use of a cover assembly  1421 . 
     It will be appreciated that cover assembly  1421  can be simply rolled up when not in use, for ease of transport and storage, similarly to cover  1100 . 
     To enable maintenance of below-atmospheric pressure in spaces  1411 , it is generally necessary to seal areas below the cover assembly  1421  such as gaps between the generator casings and bearers  1419  or floor structures (not shown). It has been found in tests that this can usually be done easily and adequately by using suitably-shaped pieces of sheet material (exemplified as  1451 ) placed in gaps and if necessary taped in place. A very suitable sheet material is of the kind formed by extrusion having twin parallel walls separated by elongate flutes or ribs therebetween, for example as sold under such names as “Corflute”. This is easy to cut to shape and reasonably robust for multiple uses, and has a degree of stiffness for resisting pressure differences. 
     A slightly different arrangement is required for spaces  1413  at ends of the MG set  1401 .  FIG. 55  shows a temporary bulkhead  1459  that is stiff enough to withstand the pressure difference associated with cleaning and that can be sealingly attached to floor structure  1461  using adhesive tape (not shown) and/or magnets or magnetic strip or strip elements in pockets  1463 . A flange (not visible) on its periphery  1465  is provided for attachment of a cover assembly  1467  similar in its construction as cover assembly  1421  to enclose space  1413 . Bulkhead  1459  may be secured to a bearing block  1409  at the outer end of generator  1405 . Bulkhead  1459  may be provided with a hinge for compact folding when not in use. As for cover assembly  1421 , additional sealing sheets (similar to sheet  1451 ) may be provided below cover assembly  1467  as required. 
     During cleaning of each of the spaces  1411  and  1413 , it is desirable that dislodged particulate matter not be simply blown into the gap between stator and armature of the motor or generator(s) adjacent to the space  1411  or  1413 , or even blown through into a neighbouring gap  1411  or  1413  communicating with the one in which a cleaning lance is in use. A simple approach is to connect only the space being cleaned to the gas-and-entrained-particulates inlet of system  30   a  (for example). 
     However, it is also possible to draw gas and particulates simultaneously from several or all of the spaces  1411  or  1413 , and to this end some embodiments provide that each duct  1415  is connectable to manifold  1417  (formed in practice using flexible hose) via a valve  1475  that can be operated together or individually under control of the data processing system (eg element  204   b  of  FIG. 41 ) so as to control the pressure in each of spaces  1411  or  1413 . For example, it is possible to provide for the space  1411  or  1413  in which lance  1447  is being used to be held at the lowest pressure of all those spaces, with progressively increasing (but sub-atmospheric) pressures being maintained in the spaces on either side of the space so that flow in the armature/stator gaps tends always to be towards the space  1411  or  1413  in which the lance is operating. 
     It will be appreciated that the method described here for cleaning sets of electrical machines can be applied to other equipment where gaps lend themselves to the use of flexible cover assemblies or can be made to do so by for example provision of components having surfaces suitable for flexible cover assemblies to attach themselves to. 
     Ventilating and Vacuuming Embodiments 
     As mentioned above, it is possible to remove particulates from a space by dislodging the particulates using gas expelled from a cleaning lance (for example lance  12 ) and drawing the gas and entrained particulates out through a duct (such as  24 ) using a vacuum source (for example blower  46  or by direct vacuum cleaning, without the use of a cleaning lance, as shown in  FIG. 1( b ) . For cleaning a particular space, both approaches may be used. 
     In some embodiments of the system  30  shown in  FIG. 2  and the system  30   a  shown in  FIG. 48 , the instrumentation and control system ( 199  or  1075 ) provides to a user the ability to select multiple modes of operation to facilitate use of both modes as required. For ease of description, this will be described by reference to system  30   a  and instrumentation and control system  1075 . 
     The control inputs (block  206   b  in  FIG. 41 ) may include a mode selection input wherein a user can select either a “blowing mode” wherein supply of cleaning gas through valve  52   a  is enabled, for operation of a cleaning lance such as lance  1160 , or a “ventilation/vacuum mode” wherein valve  52   a  is closed so that cleaning lance operation is not possible. In “ventilation/vacuuming mode”, system  30   a  becomes an instrumented system for drawing gas and entrained particulates out of a space through duct  20   a  or duct  48   a.    
     In addition to controlling valve  52   a  to allow or suppress flow through valve  52   a  according the selected operation mode, data processing unit  200   b  may also:
         enable and monitor the sensors at the stations appropriate to the selected mode, so that for example sensors at stations A, B, T are not enabled or monitored in “ventilation/vacuum mode”;   control lighting of the space being cleaned, for example by not powering lighting on lance  1160  in “ventilation/vacuum mode”;   control display (block  208   b ), alarms (block  210   b ) to operate according to the selected mode, for example not providing for alarms relating to pressure differential measured at station “T” in ventilation/vacuum mode”;   where data is to be logged during cleaning, ensuring that data applicable to the selected mode is appropriately formatted in generated files and transmitted, for example not recording a cleaning lance port in use (in embodiments where that facility is sensed) in “ventilation/vacuum mode”.       

     In further embodiments, valve  50   a  may be subject to control by data processing unit  200   b  so that a user may select (at block  206   b ), after selecting “ventilation/vacuum mode”, which of ducts  20   a  or  48   a  is to be used in “ventilation/vacuum mode”. Alternatively, there may instead simply be provided three possible modes—“blowing mode” (flow permitted through valve  52   a  and duct  20   a ), “ventilation mode” (no flow through valve  52   a , flow permitted in duct  20   a ) and “vacuum mode” (no flow through valve  52   a , flow permitted in duct  48   a ). All three of these combinations may operate best with different flow rates through blower  46   a , and data processing unit  200   b  may automatically adjust this according to the ode selected. 
     It is also possible for blower  46   a  to be provided instead or additionally with a manual speed control if required. 
     Some embodiments that enable selection of a “ventilation/vacuum mode” or of either “ventilation mode” or “vacuum mode” have a yet further enhancement. This is provision of a control output for one or more devices external to the system. For example only, a system such as system  30   a  may be employed to ventilate, and later clean particulate matter from, a space in which a power tool is used.  FIG. 56  shows schematically an arrangement in which system  30   a  is shown as a block and is used to ventilate (through duct  20   a ) later and clean a dust hood  2014  in which a power saw  2010  is being used to cut a material generating particulates. Power for saw  2010  passes from a mains supply through a relay  2012  that can switch that power on and off. Data processing unit  200   b  may be programmed to enable generation of a signal at block  207   b  ( FIG. 41 ) that operates relay  2012  to interrupt power supply to saw  2010  if a chosen sensed quantity (for example particulate concentration in ventilating duct  20   a , sensed at station “F”) exceeds a specified value. Relay  2012  may be a separate device, connected by a cable  2016  to an output location  2018  on enclosure  2002  of the major components of system  30   a , or may be incorporated in system  30   a.    
     In some applications, it may not be appropriate to cut off power to a device in this way without warning. An enhancement may therefore be provided whereby detection of excess particulates first activates an audible and/or visible alarm and then, if after a specified time particulate concentration does not fall to a satisfactory value, interrupts power to saw  2010 . Any other quantity sensed by system  30   a  may be specified to operate relay  2012 . 
     When cleaning of dust hood  2014  is required, the operating mode of system  30   a  can be changed to enable operation of cleaning lance  1160  with drawing out of particulates and gas through duct  20   a  or vacuuming through duct  48   a  as required. 
     Note that it is possible to apply system  30   a  to ventilation and/or vacuuming of spaces that are not enclosed, for example a dust hood (not shown) on or near a power tool. 
     A system such as system  30   a  may be employed as an instrumentation system only when not in use for cleaning purposes. An example is testing of a centralized industrial ventilation system (not shown) in which multiple dust hoods are connected by ducting to a central particulate collecting installation. Points in such a system may have flow rates much higher than are necessary for cleaning of individual spaces or pieces of equipment, and provided by blower  46   a . For periodic testing of the operation of such a centralized system, system  30   a  may be used with duct  20   a  acting as a sampling tube taking air and particulates from the centralized system&#39;s ducting. At the same time, a workplace particulate sensor, where included in system  30   a  would also be able to indicate whether the workplace around the ducting is safe. That is, a cleaning system according to the invention such as system  30   a  can have additional uses. 
     Pretreatment of Particulate-Laden Gas 
     The relative proportions of fine and coarse particles to be dealt with will vary from application to application, in some cases to the point where correct operation is compromised. This can be a particular problem where the proportion of relatively coarse particles is high. Taking system  999  ( FIG. 34 ) as an example, large amounts of coarse particulates may require emptying of the container  1042  more often than is desirable, may cause fouling of the fine-fraction bag and HEPA filters in casing  1040 , and cause inaccuracies in operation of the various sensors. 
       FIGS. 57 and 58  show a way of dealing with this, again using system  999  as an example. Between a container  2500  whose interior is to be cleaned and the system as described above in its enclosure  1030 , there is provided a pre-treatment system  2502 . Dust laden gas (eg air) is drawn from container  2500  through a duct  2504  as before, but instead of entering enclosure  1030  via inlet  1034 , passes into pre-treatment system  2502 . System  2502  is adapted to remove all or a large proportion of relatively coarse particulate material from this incoming gas. The gas with the unremoved portion of the particulates, then passes from an outlet  2506  through a duct  2508  and into enclosure  1030 . 
     Pre-treatment system  2502  includes an emptiable receptacle  2510  for receipt of particulates removed by system  2502 . 
     System  2502  may be designed in various ways. For example, it may simply comprise one or more woven or non-woven textile bag filters or one or more cyclone separators or any other known particulate separation device or combinations of these. 
       FIG. 58  shows in schematic form a particular realization of system  2502  that applicants have found useful and suitable for use with system  999 . Within an enclosure  2512  (represented in  FIG. 58  by chain-dotted lines) are provided two cyclone separators  2514  and  2516  whose particulate outlet ducts  2518  and  2520  direct separated particulates into receptacle  2510 . Gas entering the enclosure  2512  at inlet  2521  is split (at  2522 ) into two streams that enter cyclone separators  2514  and  2516 . Relative to receptacle  2510 , the flows in cyclone separators  2514  and  2516  are contra-rotating. This has been found useful in at least limiting movement of particulates within receptacle  2510  during use. It has also been found useful to assist in limiting movement of particulates in receptacle  2510  to extend the particulate outlet ducts  2518  and  2520  partway into receptacle  2510 . Suitable lengths for this extension will depend on design of the receptacle  2510 , and can be found by straightforward experiment or by the use of computerized fluid dynamic (CFD) methods without any need for inventive effort. 
     Outlet gas streams from separators  2514  and  2516  are combined at  2524  and directed to an outlet  2526 . From outlet  2526 , the combined gas stream passes to enclosure  1030 . 
     The use of the two separators  2514  and  2516 , instead of one, can provide better utilization of space within enclosure  2512 . Further, although  FIG. 58  shows separators  2514  and  2516  connected in parallel, it is also possible (not shown) for them to be connected in series. Moreover, it is also possible to provide multiple separators (not shown) that are differently sized and/or proportioned so as to better deal with a range of particle sizes. 
     Depending on expected particulate concentrations and cyclone separator (or other separation device) characteristics, it may be necessary or desirable to provide in system  2502  a dedicated fan or blower  2528  as shown in  FIG. 58 . 
     Instrumentation may also be provided in system  2502 . By way of example only,  FIG. 58  shows four possible stations labelled X, Y Z and W. Particulate concentration sensors may be provided at stations X and Z, with a suitable sensor for degree of filling of receptacle  2510  at station W. Where a fan or blower  2528  is provided, pressure difference between stations Y and Z may also be sensed. 
     Outputs from the instrumentation are preferably directed to, and treated as part of, the instrumentation and control system  1075  as shown in  FIG. 41 . This enables recording and display of pre-treatment instrumentation outputs and generation of alarms. Communication between the sensors of system  2502  and the remaining part of instrumentation system  1075  may be by cable or may be wireless, using any suitable digital protocol, for example Bluetooth or the like. 
     Where, as shown in  FIG. 57 , a pre-treatment system such as  2502  is used in conjunction with a main system having its own coarse particulate separation device(s) such as system  999 , the coarse particulate separation devices of the main system may or may not be used, as appropriate to their design and/or the application.  FIGS. 59 and 60  show one way in which, for system  999 , these alternatives may conveniently be handled, with a slight modification of duct  1038 . In addition to the gas inlet  1034 , there is provided a separate inlet  2530 . This inlet communicates with a duct  2532  that can receive gas from either the cyclone separator  1036  or inlet  2530 .  FIG. 59  shows gas from the system  2502  entering enclosure  1030  at inlet  1034  so as to pass through cyclone separator  1036 . A plug  2534  is placed in inlet  2530  and is shaped (as shown at  2536 ) to allow gas leaving separator  1036  to flow efficiently in duct  2532 . 
     Alternatively, as shown in  FIG. 60 , separator  1036  can be bypassed, with gas from pre-treatment system  2502  entering at inlet  2530 . Instead of plug  2534 , an adaptor tube  2538  is now located in inlet  2530 , seals off the outlet of separator  1036  and allows gas to flow past the outlet of separator  1036 , as shown by arrow  2531 . 
     Data Analysis and Reporting 
     As described above, a wide range of information can be sensed, displayed locally and/or recorded, and/or transmitted to remote locations—either within a user&#39;s enterprise or even further afield. Thus it is possible, at one level, to provide a high level of assurance to an actual user of equipment according to the invention that his or her cleaning activity is working effectively and safely or has reached a defined state of completion and safety. The user can see that the workplace is not being contaminated by fine particulates and also see that a specified degree of cleanliness is being or has been achieved—and can record proof of this. 
     At an enterprise level, management can be assured of the same things for multiple sites, machines or activities, and can store and access extensive data to enable monitoring of the time and costs involved, manage potential liability and industrial issues associated with cleaning and maintenance generally. Troublesome activities, machines or sites can be pinpointed and corrective action taken. 
     Moreover, scheduling of cleaning activities can be improved by undertaking analysis of data logged during a sequence of such activities to determine intervals between cleans that contain overall costs to a desired level. 
     Where cleaning activities are contracted to non-employees, it is possible to verify that the work is being done properly and cost-effectively. 
     Data can be transmitted beyond the enterprise so that independent verification of work done and its standards may be carried out. 
     The actual efficiency and effectiveness of different cleaning practices can be monitored using sensed data and used to identify improvements applicable not only to the particular place or activity from which the data came but to similar activities elsewhere. For example, for cleaning of a particular device or space, the required time, the best sequence for insertion of lances into port assemblies and the like can be determined and used to generate instructions (and/or computer programs where applicable) for similar activities elsewhere in the enterprise. 
     Many enterprises do not have the capability to maintain sensitive equipment and instrumentation adequately. Anomalies in data can be watched for and where these are potentially attributable to the equipment itself, corrective action sought from the equipment supplier. 
     Every system according to the invention has the capability to sample gas containing particulate material. It is possible to provide for inclusion of such system, or multiple such systems, into a data network so that such data is obtained and made available via that network whenever it is used, or remotely or automatically activate such system when it is not actually in use for the same purpose. When multiple sources of data at multiple locations (located by GPS data included in the sensed data) are provided over a data network, it can become possible through analysis to, for example, pinpoint sources of excessive particulate generation or predict where particulate matter is likely to be taken by wind. 
     All of the above activities can to some degree be automated—for example through the generation of reports by appropriate computer applications, and doing so is a part of the invention. In particular, the analysis at one location of cleaning activities from data transmitted in digital form from the actual site of the cleaning activity is a part of the invention, as is the computerized use of accumulated data over time to refine and even automate future activities. 
     Cleaning in Zones of an Enclosed Space 
     The use of gas jets to dislodge particulate matter in an enclosed space can have the effect that, after some cleaning has been done, application of a gas jet to a particular location in the space may disturb large quantities of particulates, so that locations already cleaned may be to some extent recontaminated by a cloud of particulate matter. 
     To limit this effect, it is possible to isolate, at least in part, multiple zones within the enclosed space against recontaimination. 
       FIG. 63  shows schematically a section of an enclosure  2800  whose interior is to be cleaned according to the invention, using air as a cleaning medium (although the principle is applicable also where other gases are to be used). A cover  2802  sealingly covers an opening in the enclosure  2800  and is provided with port assemblies  2804  for insertion of a cleaning lance  2806  (eg any of lances  12 ,  1160  or  2600 ). Once a zone “A” in enclosure  2800  has received at least an initial cleaning using lance  2806 , an “air curtain”  2808   a  is introduced through a nozzle  2810   a , the nozzle being elongate in a direction normal to the plane of the drawing, in known manner. Air for the air curtain  2808   a  may be obtained from the atmosphere using a dedicated blower, or the same air supply used by the equipment of the invention, or air recirculated from the air being expelled from the enclosure  2800 . Air curtain  2808   a  isolates to some degree zone “A” while cleaning proceeds in zones “B” and “C”. The process is repeated when zone “B” has been dealt with, by establishing a second air curtain  2808   b  through nozzle  2810   b . Finally, zone “C” is cleaned. 
     Depending on the particular enclosure  2800 , the particulate load therein, cleaning techinique used, and the like, it may be desirable to complete the cleaning process with further use of he lance  2806  in all three zones, with or without switching off of the air curtains  2808   a  and  2808   b.    
       FIG. 64  shows a variation on the above approach, in which an enclosure  2900  is to be cleaned. Enclosure  2900  is fitted sealingly with a cover  2902 , having port assembles  2904  for insertion of a lance (not shown) such as lance  2806 . The procedure is similar to that described in relation to enclosure  2800 , save that instead of actuating air curtains to at least partially isolate zones “A”, “B” and “C” the cover is provided with physical partitions  2906   a  and  2906   b  that can be slid inwardly and outwardly as required, through slots  2908  in cover  2902  and partitions  2906   a  and  2906   b  are slid inwardly to at least partially isolate the zones above them. 
     Additional Information on Software 
     There will now be provided a summary of software functionality adapted for cleaning applications of the invention where sophisticated control of pressure in a space being cleaned is not necessary, and not provided, and where a lance with onboard software functions such as lance  3500  is used. 
     First, the software run by a microcontroller of block  200   b  ( FIG. 41 ), consists of a start-up, a main loop and a series of interrupt driven events. On start-up, the software performs a scan of the ‘stack’ in which it is connected to determine what other layers of hardware are present. It uses this scan to enable/disable relevant sections of code accordingly. During the start up the software also uses the connected communication devices to search for and attempt to connect to other system peripherals so that they may communicate and share data. This pairing may occur in several ways, for instance, pressing a button on each device at the same time or may be set in software to automatically connect to a certain device with a given identification, if it is available. Should a connection not be established or a layer not found in the stack, the functions in the code relevant to those pieces of hardware are disabled. 
     Furthermore, with regards to enabling or disabling functionality in the code, a configuration file may be used on the SD card to determine what functions are available. Should a functionality need to be disabled or enabled for any reason outside of the relevant hardware being present on the stack, it may be done so here. Sensor ranges, set points and thresholds, as well as the unique identification of the hardware may also be found in this configuration file which is read in the start up of the device each time. This allows the same software to be loaded onto other systems according to the invention and having the functionality determined by the configuration file on the SD card which is inserted into the SD card slot on the motherboard. Authentication keys or certificates for secure transfer of data may also be stored and read from this configuration file. 
     After start up the device enters a loop. This begins by first sampling each sensor it finds on the stack sequentially. Some sensors may be sampled many times while other sensors may be sampled less frequently, depending on the importance and how rapidly the sensor may be changing. These values are then compared against set points or threshold values which determine whether the system may be operating in a failure mode, under which conditions the software shuts off the compressed air and/or motor in order to prevent operator exposure or unsafe operating conditions. A wide range of communication protocols are used to interface with the sensors. These include analogue, digital, 4-20 mA, I2C/TWI, SPI, UART, USART and USB. After sampling the values are, if required, passed through a filter to reduce noise, typically this is done through the use of a moving point average. This is used to reduce noise of data shown on displays (reducing flickering of traffic light display). The data is then logged on a SD card, if an SD card is inserted. The data may also be uploaded via 4G/WiFi using HTTP or MQTT protocols (or similar secure protocols) to a remote server if those layers of stack are included. 
     Any time during this loop, interrupt routines may occur, these are used for detecting important safety controls and button presses. For instance, the lance is able to send an interrupt if it detects a failure mode to quickly shut down the motor or the compressed air in the case of a dust leak. Accelerometers are used to detect falling or sudden impacts which may also necessitate a shut down, or, depending on magnitude of the accelerometer reading, be an indicator for mistreatment of the device. Interrupts may also be used for a microswitch which is trigged by opening the lid of the enclosure containing the main components of the system If this switch is trigged, the software on the microcontroller switches off power to prevent potentially dangerous voltages being exposed. When this interrupt is triggered, it also sounds an alarm to indicate the hazard is present and bring the users attention to the fact that power has not been disconnected properly. 
     The software also has functionality to calculate current in and out of a battery should one be attached, allowing for the battery or charge status to be estimated and displayed, recorded or transmitted to other devices. 
     The software may also communicate with a GPS if it is found on the hardware stack. With this sensor, a ‘Geo-Fence’ may be implemented with boundaries set in the configuration file found on the SD card. 
     Second, a cleaning lance such as lance  3500  may be capable of operating independently of the running software described above but also be able to communicate back and forth when paired with a system (“main system”) such as that represented with  FIGS. 41 and 48 . The lance may be used to display data from, such as, filter status or dust concentrations as well as allowing the operator to remotely control the main system, for instance, shutting down the motor in the main system from the lance. Communications may be performed using several communication protocols. These include radio (915 MHz), Bluetooth, Bluetooth LE, WiFi etc. These devices would also be found on the block  200   b  hardware stack. 
     The software on the lance is capable of producing a PWM signal of a given frequency which drives the compressed air valve. This allows for the ‘pulsed’ compressed air cleaning. 
     The air quality sensors on the lance, which detect particulate matter may be to detect whether satisfactory sealing of the area being cleaned has been achieved. If high levels of dust are detected, this is a shutdown condition. The lance software first sends an electrical signal to the valve to stop the compressed air and also uses one of the connected communication devices to send a message to the main system indicating that a shutdown is required. 
     The lance is able to capture and process images from a camera at the tip of lance. These images may be displayed on the screen for the user to view immediately, or stored on an SD so that the images may be viewed later, perhaps to evaluate state of targeted area before and after cleaning. The software may perform some image processing on these captures. 
     The lance is also able to automatically scan barcodes during use which indicate what is being cleaned at this time. This may be recorded so that any data logged at this time can be associated with the relevant truck/cabinet/motor etc. 
     Similarly, to the lance implementation, the main system may also communicate to other peripherals, such as a compressed air quality measurement unit which may send messages to both the lance and main system which may be used to shut off the compressed air should the quality be insufficient 
     The lance may similarly have accelerometers to detect dropping or sudden impacts, similarly to as described with the main system. 
     In most applications, it is expected that data logged in use of the inventive system will be transmitted to a server remote from the space being cleaned and that may itself part of the system. The data may be received using various protocols (HTTP, MQTT as examples). The data may be processed and analysed to determine filter status and device status. The software running on this server is also capable of generating CSV files. This allows the data to be viewed in widely used software packages such as Excel. The analysis and processing software on the server may also be used to generate reports indicating cleaning performance and details of the cleans performed over a given timespan. This may be generated in the form of a PDF document. This report generation may be performed automatically at a given time or a manually executed process. 
     The implementation of this software is also open, allowing for the software to be easily deployed on a physical or cloud-based server if desired. 
     COMBINATIONS OF FEATURES 
     In the above description very many of the components, features of components, system arrangements, modes of operation and the like that have been stated to have alternatives that can be used in particular applications, or added optionally or not used or implemented. Where such alternatives are described, it is intended that they may be used in combinations other than the specific combinations described, where that is practicable, and where suited to a particular application. 
     For example only, different port assemblies have been described and different cover assemblies have been described, but a port assembly described in association with a particular cover assembly may be used with another cover assembly if that is practicable.