Main Fan Research Articles

The eruptive history and volcanic hazards of Savo, Solomon Islands

Savo Island is the 6-km-diameter emergent summit of an andesitic-dacitic stratovolcano, rising from the Iron Bottom Sound, 35 km NW of Honiara, Solomon Islands. Savo has erupted at least three times within recorded history and the 3,000 inhabitants maintain extensive oral traditions of past events. Through description and interpretation of the volcaniclastic sequences on the island, in conjunction with historical accounts and oral traditions, we reconstruct the eruptive processes on Savo. Block-and-ash flow (BAF) deposits are volumetrically dominant on the island within three main depositional environments: near-vent sequences, thick medial channel sequences and distal fan sequences. The deposits comprise universally non-vesicular and highly porphyritic (40–70% phenocrysts), high-silica andesite and dacite clasts. These appear to have been derived from collapsing lava domes during an 1560–1570 A.D. eruption. However, eyewitness descriptions and crater morphology suggest that similar deposits formed from dome explosions or collapses of eruption columns during later eruptions (1830–1840 A.D.). The high-sodium magmas (ca. 5–7 wt% Na2O) apparently crystallised and strongly degassed prior to eruption. Shallow explosions were possibly caused by entrapment of magmatic gases beneath a dome or conduit plug of highly crystalline, near solid magma. Repeated sealing of the vent may have been due to inward collapse of the highly altered rocks of the surrounding hydrothermal system; these rocks probably were saturated due to contemporaneous high intensity rainfall events. BAFs were hot enough to char vegetation and attain aligned clast TRM (thermal remnant magnetism) up to 3 km from the vent, many being accompanied by ash-cloud surges. Changes with distance in the BAF deposits appear mostly dependent on flow confinement and are limited to an overall decrease in thickness and maximum clast size, and an increased definition of weak planar fabrics. In distal fan sequences, there is strong evidence for syn- and post-eruptive redeposition of primary deposits. Since the Savo population is concentrated on coastal volcaniclastic fans, we consider the greatest volcanic risk to life is from BAFs, associated ash-cloud surges and lahars. Hence, the main channels and fans are designated as the highest of three relative hazard zones on a simple map prepared to aid local education and planning initiatives on Savo.

Sediment reworking on high-latitude continental margins and its implications for palaeoceanographic studies: insights from the Norwegian-Greenland Sea

Abstract Geological evidence indicates that sediment reworking is common around the continental margins and abyssal depths of the Norwegian-Greenland Sea, a high-latitude setting with glacier-influenced margins. Detailed analysis of 22 cores up to 5 m long, placed in context by accompanying geophysical data including high resolution sub-bottom profiles, swath bathymetry and backscatter maps, indicates that reworking is variable and ranges from debris flows and turbidity currents, to bottom-current activity, as well as iceberg scouring. Reworking by debris flows appears to be restricted mainly to the main trough-mouth fans and sediment slides. Elsewhere, turbidity-current activity frequently dominates, although iceberg ploughing down to 600 m depth and current winnowing assume increasing significance on continental shelves. Reworking in the Norwegian-Greenland Sea reflects variations in ice-sheet dynamics that, in turn, influence the rate of sediment delivery and location of depocentres. Spatial variations in the style of reworking may also reflect the influence of continental slope gradient and bedrock geology on continental shelves. The widespread nature of sediment reworking has important implications for palaeoceanographic investigations in the region, as reworking can result in erosion and disturbance of the sediment column. It is estimated that less than 7% of material delivered to the Norwegian-Greenland Sea since the Late Weichselian is derived from hemipelagic and pelagic sedimentation. This problem is significant where continuous, high-resolution records of hemipelagic and pelagic sedimentation are required, and attempts are made to correlate with other high-resolution proxy records, such as ice cores, at sub-millennial scales. Bioturbation results in the smoothing of high-resolution records and imposes a maximum resolution for sediment-core time-slices of generally 400 years or more. In the Norwegian-Greenland Sea, areas of high sedimentation such as trough-mouth fans or contourite drifts are commonly associated with extensive reworking. Identification of reworking is particularly important where attempts are made to link records of iceberg-rafted debris to past ice-sheet dynamics, as bottom-current winnowing and mass-flow processes can increase the concentration of coarse-grained iceberg-rafted debris. Such localized accentuation of the iceberg-rafted debris signal may lead to erroneous palaeo-environmental interpretations. It is therefore critical that palaeoceanographic interpretations are firmly underpinned by an explicit sedimentological assessment of reworking.

Depositional landforms and environmental change in the headward vicinity of Dias Beach, Cape Point

The southern portion of the Cape Peninsula is characterised by a number of geomorphic features that reveal evidence of fluctuating sea levels and past environments. These include pronounced wave-cut platforms and the remnants of fossilised dunes. This paper reports on a unique Late Quaternary sedimentary sequence preserved within a steep-sided ravine between Cape Point and Cape Maclear at the southern tip of the Cape Peninsula. The site is situated headward of Dias Beach, where erosion has exploited a Cretaceous dolerite dyke that has intruded the Ordovician Table Mountain Group sandstone. The sediments have been incised during the Holocene, and the resultant gullies present exposed faces whose lithostratigraphy attests to a variety of geomorphic processes, which were active during the Late Pleistocene. The two main deposits reveal contrasting sedimentary structures, representing very different depositional environments. Immediately above the active dune cordon, which flanks the modern beach, a sequence of aeolianite (calcarenite) displays a variety of low-angle planar and high-angle cross bedding. This calcarenite is moderately cemented, but not completely lithified. Overlying this sequence, above an abrupt unconformity, is a massive colluvial deposit comprising unconsolidated, quartzose sand, as well as angular sandstone clasts in a number of lags. This deposit does not display any sedimentary structures. The uppermost section of the aeolianite was dated by thermoluminescence to 185 ka. The aeolian lithofacies is interpreted to be the product of aeolian deposition by onshore winds during the transition period following the 220 ka Penultimate Interglacial, the period when sea-level initiated its retreat towards the 150 ka Penultimate Glacial Lowstand. The colluvial deposit is interpreted as the midfan remains of an alluvial/colluvial fan formed by debris flow and sheetwash. Optically stimulated luminescence (OSL) dates from the base (83 ka) and the top (32 ka) of the main fan exposure suggest emplacement during the Last Glacial. Whereas the aeolianite is regarded as the product of an onshore depositional phase, the emplacement process of the colluvial fan suggests the increased presence of moisture. This, in turn, may imply a wetter environment for the southwestern Cape during the Last Glacial. It is known that the Last Glacial was generally drier over the summer-rainfall region of South Africa, but the situation for the present winter-rainfall region remains unclear. The findings from this study support the notion that conditions for the winter-rainfall region of the southwestern Cape may have been wetter prior to the termination of the Last Glacial.

Architecture of the Middle Devonian Kvamshesten Group, western Norway: sedimentary response to deformation above a ramp-flat extensional fault

Abstract The Mid-Devonian Kvamshesten basin in western Norway formed during late- to post-Caledonian extensional and strike-slip tectonics. The basin is entirely continental in origin, and was probably a closed basin through most of its history. It was filled by alluvialfluvial deposits belonging to two main terminal fan systems, one sourced in the hanging wall, one sourced in the footwall of the basin-controlling fault(s). Footwall-directed migration of the hanging-wall-sourced fluvial system probably took place during phases of relatively rapid, fault-controlled subsidence. This gave rise to retrogradational stacking of marginal conglomerates and to the footwall-directed migration of the main depocentre(s). During periods of increased sediment influx from footwall catchments and/or decreased subsidence rates, coarse, footwall-sourced material prograded far into the basin. The intercalation of material derived from footwall- and hanging-wall source areas, respectively, gave rise to a pronounced, kilometre-scale rhythmicity that is inferred to reflect fault-block rotation and footwall erosion. The basin fill also displays a pronounced rhythmic organization on the 80–150 m scale. The Kvamshesten basin was deformed during deposition as a result of its position in the hanging wall of a ramp-flat extensional fault and because of extension-parallel shortening. Thus, the pattern of subsidence was non-uniform and the sediment preservation potential varied across the basin. Deposition and preservation of floodbasin fine sediments was enhanced in areas close to the breakaway of the basin-bounding fault and in the hangingwall syncline that developed above the ramp. The crest of the rollover anticline was mainly occupied by high-energy braided fluvial systems represented by amalgamated sandstone complexes with abundant channel scour surfaces. The migration of the rollover anticline towards the breakaway of the principal basin-bounding fault resulted in the footwall-directed migration of facies belts upwards in the stratigraphy. In our interpretation, a kilometresthick, footwall-skewed amalgamated sandstone complex was constructed that marks the trace of the migrating rollover anticline through the basin stratigraphy. On the basis of stacking patterns of marginal facies, large-scale grain-size variations, the geometry of stratigraphic units and the overall lithofacies distribution, we present a sequence stratigraphic model for the basin fill. Within individual systems tracts, lithofacies distribution as well as inferred A/S ratios vary laterally because of the effects of differential subsidence and multidirectional sediment transport. Inferences of A/S ratio from vertical sections in one particular part of the basin thus cannot be used to characterize a systems tract as such. Grain-size turnarounds may, however, be used in the definition of systems tracts and sequences if the above relationships are well constrained and if turnarounds occur in stratigraphic units that are easy to correlate across the basin.

Theory and design of reversible axial fans with turn in motion blades of impeller

The scientific principles for the calculation and design of axial reversible fans with optimal aerodynamic and constructional parameters are presented. Methods of estimating the strength, dynamic stability, and life of the main fan components are proposed.

The Upper Permian Boniches Conglomerates Formation: evolution from alluvial fan to fluvial system environments and accompanying tectonic and climatic controls in the southeast Iberian Ranges, central Spain

The Boniches Conglomerates Fm. (Upper Permian) represents the first episode of sedimentation in the southeast border margin of the Iberian Basin, central Spain. The Iberian Basin commenced development as a rift basin running mainly NW-SE during the Early Permian and underwent its first general extensional period during the Late Permian. The Boniches Fm. was deposited as a small segment (less than 100 km long and 9–10 km wide) of the Iberian Basin that extended in a northeast direction during this period. Detailed mapping and palaeocurrent analysis have shown that the Boniches Fm. is of a curvilinear, wedge-shaped morphology. Sediments close to the southwest main faulted border are of a maximum thickness of 230 m. Clear lateral variation in thickness controlled by the activity of secondary transfer faults perpendicular to the main NW-SE axis may be observed. This network of faults permitted the formation of blocks, limited laterally by the transfer faults. These blocks experienced subsidence and rotation against the elevated southwest footwall block which resulted in the isolation of reduced sub-basins with different sedimentary characteristics. Based on facies and facies association, the Boniches Fm. is thought to have evolved vertically from two main alluvial fan systems in the lowest part of the formation, into fluvial braided systems flowing southeast. As expected, no flow orientations towards the footwall block are observed during the first episodes of the refill. This may be explained by erosion, or simply a lack of sedimentation due to the gentle slope. The change from alluvial fan to fluvial environments is interpreted as a relatively sudden tectonic reorganization of the whole segment favouring new longitudinal fluvial drainage from a transfer zone located to the northwest. Three different reorganization episodes, clearly marked in the Boniches Fm. as ‘main boundary surfaces’ (MBS) separate four members subdivided into 4–5 levels (3–4 m thick). Each level consists of fining-upward successions less than 1 m thick. Tectonics and climatic factors clearly controlled sedimentation. Tectonic activity was probably of greatest importance and was conditioned by the movement of the main NW-SE and NE-SW transfer faults. The role of climate in ancient conglomerate sediments has not been well established. Palaeogeographical, mineralogical, sedimentological and clast analyses suggest that the Boniches Fm. was deposited under humid conditions by running water. The differentiation between ‘proper’ alluvial fans and fluvial environments during the transition period of the Boniches Fm.is not clear since, in many recent alluvial fans, braided fluvial systems are associated with fans.

Active thrust tectonics in western Sicily (southern Italy): the 1968 Belice earthquake sequence

ABSTRACTThe 1968 Belice earthquake sequence, characterized by six main shocks with 5 < M < 5.4, represents the strongest seismic event recorded in western Sicily in historical times. The epicentral area is located in the Belice Valley, a region lacking any topographic lineament likely to result from a fault with significant offsets of any kind. Instrumental data show that hypocentres of the major shocks are distributed along a roughly N‐dipping plane extending from about 36 km to 1 km depth. Fault plane solutions show pure thrusting mechanisms on N‐dipping, ENE‐trending planes, or oblique slip with a right‐lateral component of motion along steep WSW‐dipping planes, both as a result of approximate N‐S shortening. The observed destruction indicates that isoseismal areas are elongated in an ENE direction. Similarly, the epiccntral distribution of events with M ≥ 4 outlines a roughly elliptical ENE‐elongated area located 20 km NW of the Sciacca‐Rocca Ficuzza thrust front. This ENE‐striking structure, representing the regional morphotectonic feature closest to the epicentral area, consists of two main imbricate fan systems. In the southernmost system, Quaternary deposits (tentatively dated as 1.0–0.7 Myr old) are involved in a large ramp anticline uplifting them to a maximum altitude of 346 m. The occurrence of Holocene lacustrine piggy‐back basins on the rear of this structure also indicates late Quaternary activity of the underlying thrust. Seismological, structural and morphotectonic observations suggest that multiple ruptures might have occurred during the 1968 sequence on a blind crustal thrust ramp located beneath the epicentral area. Slip propagated southwards along the shallow ramp‐flat system characterizing the thin‐skinned foreland fold and thrust belt of southwestern Sicily, being dispersed in flexural folding processes and diffuse strain along this path.

ファン特性変更と通気抵抗調節による通気網の最適化

This paper proposes a new method for optimization of ventilation network with a main fan in terms of minimization of the total cost which consists of the cost of power for ventilation and that of controlling resistances of airways. The elements to be considered in this method are the fan characteristics and resistances of the network. The proposed method yields the optimum fan operating point and resistances to be controlled. The following results are obtained through analyses of some examples by this method:1. More energy saving control of ventilation network can be attained by the proposed method which considers fan characteristics than by others which do not.2. Results computed by this method may notmake optimized values, when improper initial values of fan characteristics and resistancesare used. However, the optimum values will be gained by calculating again using the results of the previous calculation as the initial values for the subsequent trial.3. Optimization is better when the required air quantities are constrained by lower and upper boundthan when given as fixed values.

Cost-effective prevention of equipment failure in the mining industry

To operate successfully in a competitive world catastrophic failures need to be prevented. This can be achieved by implementing a balanced approach which covers all phases of the life cycle of equipment. To gain maximum benefit, the effective prevention of failures should involve a team of people ranging from the supplier to the maintenance personnel on site. Initially, the logic and main elements of the approach are discussed, whereafter the practical implementation and benefits are illustrated by means of two case studies comprising, respectively, a bucket wheel excavator and a main ventilation fan.

INFLUENCE OF TEMPERATURE AND PHOTOPERIOD ON FLOWERING OF ANIGOZANTHOS HYBRIDS

Flowering responses of two Anigozanthos hybrids were investigated. Flowering of 20-week old `Regal Claw' and A. manglesii x A. flavidus either from the main fan or the lateral fans was accelerated when plants received a night temp of 13 C, regardless of the photoperiod treatments. Temperature was the major factor controlling flowering of Anigo- zanthos hybrids. Flowering was accelerated from the lateral fans by treating plants at 15.5 or 18 C and a long day (LD) photoperiod. There were fewer than 2.5 branches in the stem at 18 C compared to more than 4.0 branches at 13 C. A night temp of 13 C was optimum for early flowering and for increased quality of cut flowers. At an inductive night temp of 13 C, Anigozanthos hybrids are day neutral while at 15.5 or 18 C they are quantitative LD plants.

地下通気網における気流温度・湿度予測解析システム

This paper describes a new practical method for predicting environmental airflow-conditions, such as temperature and enthalpy, in underground ventilation networks. The calculation code “MIVENA” for mine ventilation networks has developed by authors using with a nodal head method and the temperature-humidity prediction method. The equations and schemes fitted to the network calculations are presented clearly as a general form. The system was mostly compared with Amano et al.'s system and differences between two systems are discussed.The prediction method is that the environmental airflow-conditions on nodes are calculated from inlet nodes to downstream nodes and ones on the fan node can be calculated at last. The environmental conditions of inflow airstream on airways connected to a node are calculated from upstream to downstream with a kind of one dimensional numerical-difference methods by dividing the airways to 5 m long spans before the calculations of the node.The temperature and humidity on nodes consisting of the recirculation loop can be calculated by using a function which indicate a approximation degree of the calculation result. When absolute humidity in airflow becomes larger than saturation absolute humidity on airways or nodes, the methods and calculation schemes for revisions of temperature and humidity are also presented. These methods are effective for calculations on exhaust airways which are influenced by auto-expansion with temperature reduction.The present calculation system was successfully applied to the Amano et al.'s network example, the Ezuri Mine and the Fukasawa Mine run by Hanaoka Mining Co. LTD. Fan driving maps for main fans controlled by thylisters, which indicate the total inlet airflow-quantity on several seasons against the thylister frequency, were made to find out the optimum driving thylister frequency on each season.

マトリックス解法を用いた節点法による通気網解析

This report describes a calculation method for mine ventilation networks with a nodal head method.The generalized equations and calculation methods for solving a steady-state mine ventilation network have been written to clear the algorism of a computer program.The use of the modified Choleski's decomposition algorism has an advantage of rapid convergence to solve the linear system for the pressure corrections of nodes consisting of a symmetric matrix.The four examples of the mine ventilation networks, of which the total numbers of the nordes N are 8, 14, 51 and 141 respectively, were calculated with a personal computer (640KB, MS-DOS system). As the convergence criterion, it was employed that the maximum tolerance of the summed flow-rates in continuity at each node is less than 0.1 m3 /min. Under the condition that the pressure of the main fan is kept constant and the acceleration constant for convergence is taken 1.4, the numbers of the iteration until the convergence are nearly 13 for each example. The CPU times of an iteration are roughly in proportion to N3/2.

Ventilation of a dead‐end duct having a porous barrier

AbstractAnalytic expressions for the flow and pressure in a dead‐end duct which has loss of fluid through a porous wall are developed. The presence of an obstruction or auxiliary fan at the end of the duct is included. In either case there is a maximum permissible length of duct. As the duct length approaches this maximum, the main supply fan power and flow increase dramatically.There is no recirculation within the duct when there is an obstruction at the end of the duct. If an auxiliary fan is used, there is always recirculation. However the use of an auxiliary fan can yield major savings in total power requirements.

Calculations for emergency ventilation conditions in mines with several main fans

When accidents happen in mines ventilated by several main fans it becomes necessary to redistribute airflows inside the network both in magnitude and direction. New conditions have to be defined for the combined operation of the fans which differs from normal operation. The authors present factors which must be taken into account when selecting the possible alternatives of the reversion of fans. An equation is given for the influence experienced by the network ventilation from these factors. Pressure characteristics of workings for various configurations of ventilation systems are shown. The search for the operation conditions of the system of fans is reduced to a discrete programming problem.

Experiments with Air Flow Control in a Coal Mine

The problem of automatic control of a coal mine ventilation network is discussed. It is found that the structure of the control system should have two levels, i.e. local regulation of ventilation parameters (air flows) in faces to eliminate the effect of quick disturbances, and supervisory control of the whole ventilation process by periodical modifications to the working characteristics of the main fans. Practical and theoretical problems connected with implementation of the system in Polish mining are listed and discussed. To solve these problems a series of experiments with air flow control in three different coal faces were carried out with the aim of checking the measuring and control equipment in & real mine conditions as well as investigating the gasodynamics of the ventilation process. The results of the experiments are analysed, and used to verify the mathematical model of the gasodynamics of a longwall face

Laacher See Tephra: A widespread isochronous late Quaternary tephra layer in central and northern Europe

A late Quaternary tephra layer, widespread in central and northern Europe, resulted from explosive Plinian and phreatomagmatic eruptions of the Laacher See Volcano 11,000 yr B.P. The tephra is distinguished from other late Quaternary andesitic-rhyolitic airfall tuff layers in northern Europe and from basaltic or trachytic tuff deposits in southern Europe by its phonolitic composition and abundance of sanidine, plagioclase, clinopyroxene, amphibole, and sphene. The proximal tephia sequence at Laacher See is divided into three main deposits: the predominantly Plinian deposits of Lower and Middle Laacher See Tephra (LLST and MLST) and phreatomagmatic deposits of the Upper Laacher See Tephra (ULST). The MLST member is further subdivided into beds A, B, and C1, C2, and C3. The chemical composition of the magma is highly differentiated phonolite in the LLST to MLST B sections but mafic phonolite in the MLST C1 to ULST sections. All deposits are considered to be isochronous, the frequency maximum of 16 radiocarbon datings indicating an eruption about 11,000 ±50 yr B.P. Distal ash was deposited in three main fans directed to the northeast (LST traced up to 1,100 km distance), south (LST traced up to 600 km), and southwest (LST traced up to 100 km). Tephrostratigraphic correlation of the distal ash deposits is based on (a) the major-element composition of glass shards, (b) lithology, and (c) heavy-mineral analyses. The northeastern fan consists of deposits from LLST, MLST B, and MLST C1 eruptive phases, the southern fan comprises MLST A, MLST C2, and ULST deposits, and the southwestern fan consists exclusively of ash from the ULST eruptive phase. Northeastern transport of ash during eruptive phases, with high Plinian eruption columns, but southern and southwestern transport of ash along phases of relatively low eruption columns, are interpreted in terms of prevailing southwesterly paleowinds at high altitudes (tropopause level?) but northerly winds dominating in the lower atmosphere. The Laacher See eruption columns were emplaced into an atmosphere vertically zoned with respect to paleowind directions, which also explains the near-vent shifting of LLST, MLST B, and MLST C1 iso-pach axes from east-southeast to northeast within the first 20 km of transport.

Reverse performance characteristics of main mine fans

During a mine fire or other emergency, it may be desirable to reverse the airflow in order to provide an escapeway or to isolate a fire. Also, in colder areas, the airflow may be reversed to prevent ice buildup. When reversing main mine fans, the mine operator usually does not know what operating characteristics of flow and pressure to expect. Laboratory and field tests of vane axial main mine fans were conducted to establish forward and reverse performance characteristics under controlled conditions and in typical mine installations. All fans tested were between 81 and 96 in. (2.1 and 2.4 m) in diameter. The data obtained suggest that reverse performance characteristics are dependent upon the blade angle and the hub to tip ratio. There is also evidence that reverse performance can be perdicted for a family of blade angles for a given hub to tip ratio. Generally fan quantity is 30–60% less in reverse than when operating in the normal forward mode, with static pressure equal to the square of the volume percentage change.

Sound dome for electric vacuum cleaner

The disclosure concerns a sound dome which is positioned over the motor housing of a bypass type vacuum cleaner. The main housing outlet for the main blower fan of the vacuum cleaner opens under the sound dome. The dome outlet from the sound dome is spaced away from the main housing outlet, causing the air from the main housing outlet to be redirected to the dome outlet. The motor housing has a tower portion that extends up into the sound dome. The housing has a cooling air inlet for cooling air to the motor, which is located higher up on the tower, and has a cooling air outlet for air that has cooled the motor, which is located lower on the tower. A baffle in the sound dome separates the cooling air inlet and the cooling air outlet. The enlarged plenum defined by the sound dome and the indirect pathway between the main housing outlet and the exit from the sound dome tend to reduce the noise generated by the vacuum cleaner.

A general method of optimization of the flow distribution in a complex ventilation network

One of the most complicated stages in the creation of mathematical techniques for automation of coal mines is the development of methods, algorithms, and programs for making computerized calculations concerning ventilation. In planning the ventilation of new and reconstructed pits, it is necessary to choose optimum parameters and types of main and local ventilator fans, to regulate the network with the aid of additional regulating devices, and to determine the aerodynamic parameters of all branches of the network. The most general mathematical formulation of the problem of optimum current distribution appears as follows: we are to find the aerodynamic resistance of the additional regulating devices, the air flow rates in all branches of the network, and the depressions and outputs of the sources of draft which minimize an objective function, namely the energy expended on ventilation of the network. We must satisfy certain physical and technological constraints which are described. Our investigations have shown that an algorithm for decomposition of the network laws must be adaptive and self-adjusting in the course of the process in order to improve the convergence of the calculation. This is achieved by periodic changes in the mathematical model of the network, i.s., the system ofmore » fundamental nodes and the system of independent cycles. The rate of convergence of the iterative processes of flow and depression optimization is most markedly influenced by the ratio of the sum of the resistances of the branches of the tree and antitree with allowance for the constraints on the flows and depressions.« less

A method of calculating the natural ventilating pressure created by a main fan

1. The thermodynamic method of determining the natural ventilating pressure in a real circuit in which a ventilator (fan) is working in terms of the measured temperatures of the air does not take account of the natural draft due to the operation of the ventilator. 2. The work done by 1 kg of air along a contour closed through the ventilator in HT coordinates is equal to an area bounded by a contour with coordinates of points given by Eqs. (1)–(7) to the position of the free atmosphere, divided by the absolute temperature corresponding to the centroid of the area. The work per cubic meter of air will also be the total natural ventilating pressure along the given contour, including that created by the fan working in it. 3. The hydrostatic method of determining the natural ventilating pressure from the true mean densities of the air in the intake and return streams enables us to find correct results which take account of the natural draft created by the work of the fan. 4. The additional natural ventilating pressure due to the operation of the fan can be found from Eqs. (11) and (12), is directed in the same sense as the depression of the fan (ventilator), and should be taken into account in calculating the design parameters of high-pressure fans for deep pits. 5. Artificial ventilation of pits creates a cooling (exhausting ventilation) or warming (forced ventilation) effect, which is proportional to the depression of the fan (ventilator) for the given point, and is very marked for pits with high-pressure fans.