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Negative pressure

Negative pressure, in the context of physics and engineering, refers to a condition where the pressure exerted by a fluid or gas is lower than the reference pressure, most commonly atmospheric pressure, resulting in a negative gauge pressure measurement while the absolute pressure remains positive above zero.^[1] This concept is fundamental in applications such as vacuum systems, where sub-atmospheric conditions create suction effects to draw fluids or gases toward the lower-pressure region.^[2] In advanced physical theories, particularly cosmology, negative pressure describes an exotic state where the pressure P is negative relative to the energy density \rho, often expressed as P = -\rho c^2, with c being the speed of light.^[3] This property is attributed to vacuum energy or dark energy, which generates a repulsive gravitational effect, driving the accelerated expansion of the universe on large scales.^[4] Such negative pressure distinguishes this form of energy from ordinary matter and radiation, which exhibit positive pressure, and it plays a key role in models like the cosmological constant.^[3] Beyond physics, negative pressure finds critical applications in medicine, notably in negative pressure wound therapy (NPWT), a technique that applies controlled sub-atmospheric pressure to chronic or acute wounds to remove excess fluid, reduce edema, and promote tissue perfusion and healing.^[5] Similarly, in respiratory care, negative pressure ventilation involves devices that generate suction around the thorax or body to expand the lungs and assist breathing, as seen in historical iron lung systems and modern noninvasive methods for treating respiratory failure.^[6] These medical uses leverage the suction effect of negative pressure to improve patient outcomes in wound management and ventilatory support.^[7]

Fundamentals

Definition and Concepts

Negative pressure, in physical terms, refers to any pressure that is less than the reference atmospheric pressure, which is standardized at 101.325 kPa at sea level. This concept is distinct from a perfect vacuum, as negative pressure still involves the presence of matter exerting force, albeit reduced compared to ambient conditions; it ranges from just below atmospheric levels down to, but not including, absolute zero pressure. In practice, it is commonly measured using gauge pressure, where values below zero indicate a partial vacuum relative to the surrounding atmosphere.^[8]^[9]^[10] A key distinction exists between relative negative pressure and absolute negative pressure. Relative negative pressure, or negative gauge pressure, describes suction effects below ambient pressure, where the fluid or gas is pulled toward lower-pressure regions without implying tension below absolute zero; this is stable and common in engineering contexts. In contrast, absolute negative pressure occurs in metastable states, particularly in liquids under tension, where cohesive forces prevent phase change despite the pressure dropping below the vapor pressure and absolute zero—this creates tensile stress akin to pulling the liquid apart at a molecular level.^[9]^[11] Basic examples illustrate these concepts. A household vacuum cleaner generates localized negative gauge pressure, typically around 20 kPa below atmospheric, to draw in air and particulates through suction. Similarly, in weather systems, barometric pressure drops in low-pressure areas—such as cyclones—create relative negative pressure gradients compared to surrounding regions, prompting air inflow and storm development.^[10]^[12] Conceptually, negative pressure can be visualized on a pressure scale: absolute zero (perfect vacuum) marks the baseline at 0 Pa, with standard atmospheric pressure at 101.325 kPa above it; positive pressures extend upward for compressed states, while the negative gauge region lies between atmospheric pressure and absolute zero, and the negative absolute region dips below zero in tensile scenarios. This framework highlights how negative pressure drives flows and forces without reaching true emptiness.^[8]^[9]

Units and Measurement

Negative pressure, often referred to in the context of vacuum measurements, is quantified using standardized units that reflect the degree of pressure below atmospheric levels. In the International System of Units (SI), the pascal (Pa) serves as the primary unit for pressure, where negative pressures are expressed relative to atmospheric pressure (approximately 101,325 Pa at sea level).^[13] Commonly used units for gauge vacuum measurements include inches of mercury (inHg), millimeters of mercury (mmHg), and torr, particularly for low-pressure applications; for instance, 1 torr is defined as exactly 1 mmHg, equivalent to 133.322 Pa.^[14] These units are widely adopted in engineering and scientific contexts due to their historical basis in mercury barometry and practical utility in vacuum technology.^[15] Distinctions between gauge and absolute pressure scales are essential for accurate interpretation of negative pressure values. Gauge pressure (P_{gauge}) is calculated as the difference between absolute pressure (P_{absolute}) and atmospheric pressure (P_{atmospheric}), such that P_{gauge} = P_{absolute} - P_{atmospheric}; negative values of P_{gauge} indicate pressures below ambient atmospheric levels, commonly used to describe vacuums in practical systems.^[9] In contrast, the absolute pressure scale ranges from 0 Pa, representing a perfect vacuum, to positive values increasing with pressure, providing a reference independent of local atmospheric conditions.^[16] This absolute scale is critical for precise scientific measurements, while gauge readings are more intuitive for industrial applications involving suction or partial vacuums.^[17] Various devices are employed to measure negative pressure, selected based on the vacuum range and required precision. Bourdon tube gauges, which operate on the principle of a curved metal tube expanding or contracting under pressure differences, are suitable for rough to moderate vacuums down to about 1 torr (133 Pa), offering robust mechanical reliability in industrial settings.^[18] For lower pressures in the range of 10^{-3} to 10 torr, Pirani gauges utilize thermal conductivity by heating a wire and measuring its resistance change due to gas molecule interactions, providing indirect but effective vacuum assessment.^[19] High-vacuum measurements, down to 10^{-6} torr or lower, rely on McLeod gauges, which employ a volume compression method to isolate and measure gas pressure through mercury displacement, serving as a primary standard for calibration despite their non-continuous operation.^[20] Calibration of these measurement devices adheres to established standards to ensure accuracy and traceability. The National Institute of Standards and Technology (NIST) provides calibration services for vacuum gauges across ranges from 10 kPa to ultra-high vacuums, using primary standards like the pulsed constant-volume apparatus to achieve uncertainties as low as 0.1% in controlled conditions.^[21] Similarly, the International Organization for Standardization (ISO) defines characteristics in standards such as ISO/TS 6737 for stable ionization vacuum gauges, enabling reference calibrations with uncertainties below 1% in high and ultra-high vacuum ranges.^[22] For digital manometers used in vacuum applications, typical accuracy levels reach ±0.25% of full scale, as verified through NIST-traceable calibrations that account for temperature and linearity errors.^[23] These standards enable reliable quantification of negative pressure, minimizing systematic errors in diverse applications.

Physical Principles

Thermodynamics and Metastability

In thermodynamics, negative absolute pressure denotes a state where the pressure P < 0, manifesting as tensile stress within a liquid that is sustained by intermolecular cohesive forces, thereby preventing structural collapse and enabling the formation of stretched or superheated liquid phases.^[24] This condition arises when the liquid is subjected to pulling forces that expand its volume beyond equilibrium, yet molecular attractions maintain cohesion, contrasting with the compressive nature of positive pressures.^[25] Such states are thermodynamically possible in condensed phases like liquids, where the equation of state allows for negative pressure regimes without immediate phase transition.^[25] Metastability under negative pressure occurs when a liquid, such as water, sustains tensions up to -20 MPa in controlled laboratory conditions while remaining in the liquid phase below its vapor pressure, primarily due to the absence of nucleation sites that would initiate vapor bubble formation.^[26] In this regime, the liquid exists in a non-equilibrium state, where thermal fluctuations are insufficient to overcome the energy barrier for phase change without heterogeneous catalysts like impurities or container walls. Experiments have achieved tensions up to -140 MPa in pure water before spontaneous cavitation occurs. The ultimate limit of this metastability is defined by the spinodal decomposition curve, beyond which the liquid becomes mechanically unstable, and spontaneous phase separation occurs without a nucleation barrier, typically at pressures around -140 MPa for water at room temperature.^[27] The Gibbs free energy change for phase stability, given by \Delta G = V \Delta P - S \Delta T (where V is volume, S is entropy, and \Delta P, \Delta T are changes in pressure and temperature), illustrates this: negative \Delta P increases \Delta G for vaporization, raising the energy barrier and enhancing stability against cavitation.^[25] Historical investigations into these phenomena began with Marcellin Berthelot's experiments in the 1850s, where he used sealed glass tubes partially filled with liquid and heated them to generate negative pressures through thermal expansion, demonstrating superheated states without boiling until mechanical rupture occurred.^[28] Modern studies extend this to biological systems, such as tree xylem sap, where negative pressures ranging from -1 to -10 MPa drive water transport via the cohesion-tension mechanism, with measurements confirming these tensions in various species under natural conditions.^[29] These metastable configurations store potential energy equivalent to the work done in stretching the liquid, which is abruptly released upon cavitation, converting tensile strain into kinetic energy through bubble formation and collapse.

Fluid Dynamics and Cavitation

In fluid dynamics, negative pressure arises primarily through the application of Bernoulli's principle, which describes the conservation of energy along a streamline in an inviscid, incompressible flow. The principle is expressed by the equation

P + \frac{1}{2} \rho v^2 + \rho g h = \constant,

where P is the static pressure, \rho is the fluid density, v is the flow velocity, g is gravitational acceleration, and h is the elevation. As local velocity v increases—such as in constrictions, around curved surfaces, or over accelerating flows—the dynamic pressure term \frac{1}{2} \rho v^2 rises, causing a corresponding drop in static pressure P to maintain the constant total energy. This pressure reduction can result in sub-atmospheric or negative gauge pressures relative to ambient conditions, particularly in high-speed flows where velocity gradients are steep.^[30]^[31] When the local static pressure falls below the vapor pressure of the liquid (P_v), cavitation occurs, defined as the formation of vapor-filled cavities or bubbles within the liquid. For water at 20°C, the vapor pressure P_v is approximately 2.3 kPa, meaning cavitation initiates if the pressure drops below this threshold despite the liquid remaining below its boiling point at ambient conditions. These bubbles form rapidly in low-pressure zones but collapse violently upon entering higher-pressure regions, generating localized shock waves due to the implosive compression of the vapor. The collapse mechanics involve asymmetric bubble dynamics near solid surfaces, producing microjets and pressure pulses up to several thousand atmospheres, which can erode materials through repeated impacts.^[32]^[33]^[34] The onset and severity of cavitation in flowing fluids are quantified by the cavitation number \sigma, given by

\sigma = \frac{P - P_v}{\frac{1}{2} \rho v^2},

where P is the reference static pressure (typically far-field), and the denominator represents the dynamic pressure. Cavitation is prone in regions where \sigma < 0, indicating that the local pressure has dipped below P_v, creating negative pressure zones that favor bubble nucleation and growth. Low or negative \sigma values correlate with intensified bubble dynamics and potential damage, guiding the analysis of flow regimes in engineering designs. A prominent example of cavitation induced by negative pressure is the erosion of ship propeller blades, where high rotational speeds generate low-pressure faces on the blades, often exacerbated by tip vortices. As blades rotate through non-uniform wake flows, local pressures drop below P_v, forming cavities that collapse near the blade surface, leading to pitting and material loss over time—sometimes reducing propeller efficiency by up to 20% in severe cases. Similarly, in hydraulic systems, pumps can induce cavitation if suction-side pressures become sufficiently negative due to high flow demands or restricted inlets, causing vapor bubbles to form at the impeller eye and collapse downstream, resulting in noise, vibration, and performance degradation.^[35]^[36]^[37] To mitigate cavitation in such systems, engineers employ net positive suction head (NPSH) calculations, ensuring the available NPSH (NPSH_a)—the excess pressure at the pump inlet above P_v, accounting for elevation, friction, and velocity head—exceeds the required NPSH (NPSH_r) specified by the pump manufacturer. This condition, NPSH_a > NPSH_r (typically with a margin of 0.5–1 m of liquid head), prevents negative pressure buildup at critical points, avoiding bubble inception and maintaining stable operation.^[38]^[39]

Medical Applications

Ventilation Systems

Negative pressure ventilation (NPV) systems replicate the physiological process of breathing by generating subatmospheric pressure around the chest and abdomen, which lowers external pressure and creates a gradient that draws air into the lungs for expansion. This approach typically employs pressure drops ranging from -15 to -25 cmH₂O, titrated based on patient response and device capabilities.^[40] The foundational device in NPV history is the iron lung, invented in 1928 by Philip Drinker and Louis Shaw at Harvard University School of Public Health, which encased the patient's body (except the head) in a sealed cylindrical chamber to cyclically apply negative pressure during inspiration. This generated pressures of -15 to -25 cmH₂O, aiding diaphragmatic movement in paralyzed patients. The iron lung saw widespread use during the polio epidemics of the 1940s and 1950s, saving thousands of lives by supporting respiration in victims of bulbar and spinal polio who suffered diaphragmatic paralysis; for instance, over 1,200 iron lungs were in operation across U.S. hospitals by the mid-1950s, treating affected individuals amid outbreaks that paralyzed up to 58,000 Americans annually.^[41]^[40]^[42] Contemporary NPV devices have evolved to address the bulkiness of early models, with cuirass ventilators utilizing a lightweight shell that partially encloses the anterior chest and upper abdomen, allowing intermittent negative pressure application while permitting easier patient access and mobility. Biphasic cuirass ventilation (BCV) systems represent a modern advancement, alternating negative pressure for inspiration with positive pressure for expiration to optimize tidal volume and secretion clearance. Compared to positive pressure ventilation, NPV reduces the incidence of barotrauma by avoiding direct inflation of the airways and lungs, thereby minimizing risks of volutrauma and hemodynamic instability.^[43]^[44]^[45] Clinically, NPV is particularly indicated for neuromuscular diseases such as amyotrophic lateral sclerosis (ALS), where progressive respiratory muscle weakness leads to hypoventilation and hypercapnia; it supports nocturnal or daytime ventilation in patients intolerant to mask-based noninvasive positive pressure ventilation due to bulbar dysfunction or claustrophobia. Additionally, NPV facilitates weaning from invasive positive pressure ventilation by enhancing ventilation-perfusion matching and carbon dioxide clearance, as demonstrated in cases of prolonged extracorporeal membrane oxygenation support where adjunctive cuirass NPV enabled successful decannulation after extended dependence.^[46]^[47] Key limitations of NPV include positioning constraints, as full-body or cuirass devices often necessitate a supine or semi-recumbent posture to maintain an airtight seal, which can exacerbate discomfort, pressure sores, or orthopnea in patients with kyphoscoliosis or abdominal issues. Efficacy data from 2020s studies on chronic respiratory failure in neuromuscular contexts show success rates of approximately 80% in averting intubation or stabilizing ventilation among small cohorts, though broader application is hindered by equipment availability and patient tolerance.^[46]^[46]

Wound Therapy

Negative pressure wound therapy (NPWT), also known as vacuum-assisted closure, is a therapeutic technique that applies subatmospheric pressure to wounds to promote healing by managing exudate, stimulating tissue growth, and reducing infection risk.^[48] This method involves placing an open-cell foam dressing over the wound, sealing it with an adhesive film, and connecting it to a suction pump that generates controlled negative pressure, typically in the range of -80 to -150 mmHg, either continuously or intermittently.^[49] The therapy removes excess fluid and infectious material while mechanically influencing the wound bed to accelerate granulation tissue formation.^[50] The technique was developed in the early 1990s and first commercialized by Kinetic Concepts Inc. (KCI) with the V.A.C. Therapy system, which received U.S. Food and Drug Administration (FDA) 510(k) clearance in 1995 for treating chronic wounds.^[51] Initial clinical descriptions by Argenta and Morykwas in 1997 highlighted its efficacy in promoting granulation and healing in complex wounds, building on earlier experimental work with suction in animal models.^[52] Since its introduction, NPWT has evolved into a widely adopted standard for managing difficult-to-heal wounds, with ongoing refinements in portable and single-use devices.^[53] At the core of NPWT's mechanism is the application of negative pressure through a sealed system: the foam dressing interfaces directly with the wound bed, allowing even distribution of pressure while facilitating drainage; a connecting tube links it to a canister that collects exudate; and the pump maintains the vacuum.^[54] This setup applies subatmospheric pressure, commonly set at -125 mmHg, which draws wound edges together (macrostrain) and creates localized deformations at the cellular level (microstrain), stimulating cell proliferation and angiogenesis.^[55] The continuous or intermittent suction removes interstitial fluid and bacteria-laden exudate, creating a moist but controlled wound environment that fosters healthy granulation tissue over irregular surfaces.^[56] Protocols adjust pressure based on wound type—for instance, lower settings around -80 mmHg for fragile skin or higher up to -150 mmHg for deeper cavities—to optimize outcomes while minimizing discomfort.^[57] Physiologically, NPWT enhances wound perfusion by increasing blood flow to the wound bed through mechanical forces that reverse hypoperfusion common in chronic wounds.^[58] Macrostrain from tissue expansion promotes approximation of wound margins and removal of slough, while microstrain triggers intracellular signaling pathways that boost fibroblast activity and collagen deposition.^[59] These effects collectively reduce edema by facilitating lymphatic drainage and fluid evacuation; experimental studies in animal models have shown edema reductions of up to 50% in treated incisions compared to controls.^[60] Overall, this leads to improved oxygenation and nutrient delivery, accelerating the transition from inflammation to the proliferative phase of healing.^[61] Clinically, NPWT is particularly effective for diabetic foot ulcers (DFUs), where it promotes faster closure and reduces amputation risk compared to standard moist dressings.^[62] In surgical incisions at high risk for dehiscence, such as those in contaminated or obese patients, NPWT minimizes seroma formation and infection rates.^[63] A 2023 evaluation of NPWT in DFUs demonstrated significantly higher healing rates, with complete closure achieved in a greater proportion of cases versus conventional therapy.^[64] A 2025 meta-analysis indicates that NPWT improves wound healing rates with a risk ratio of 1.46 (95% CI: 1.22–1.76) compared to conventional therapy.^[65] These benefits are most pronounced in moderate-to-severe cases, though outcomes vary by patient comorbidities and adherence to therapy protocols.^[66]

Isolation and Containment

Negative pressure isolation, also known as airborne infection isolation rooms (AIIRs), operates on the principle of maintaining a lower air pressure within the room compared to adjacent areas, typically a differential of at least -2.5 Pa (-0.01 inches of water gauge), achieved by exhausting more air than is supplied. This setup, often incorporating high-efficiency particulate air (HEPA)-filtered exhaust systems, ensures that air flows inward from surrounding spaces, containing potentially contaminated aerosols and preventing their escape into hallways or other patient areas.^[67] The exhaust air is directed outward through HEPA filters to capture 99.97% of particles 0.3 micrometers or larger, further minimizing environmental release of pathogens.^[68] Guidelines from the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO), updated in 2024 following the COVID-19 pandemic, emphasize the use of AIIRs for containing airborne pathogens, with requirements for at least 12 air changes per hour and direct exhaust to the outdoors or through HEPA filtration.^[69] Monitoring of negative pressure is recommended daily while the room is occupied, using visual indicators such as smoke tubes or tissue tests to confirm inward airflow direction, with continuous monitoring preferred in high-risk settings via differential pressure gauges.^[67] These standards ensure the room's integrity, with documentation required to verify functionality and prevent lapses that could lead to transmission.^[70] AIIRs are primarily applied in healthcare facilities for isolating patients with airborne infectious diseases such as tuberculosis (TB) and measles, where the risk of aerosol generation is high during coughing or aerosol-generating procedures.^[71] They are also utilized in surgical suites for procedures involving implants or high-risk airborne precautions, such as those for varicella or SARS-CoV-2 cases, to protect staff and adjacent areas.^[72] Historically, negative pressure isolation emerged in the 1970s for TB management in hospital settings, evolving from earlier sanatorium practices, and saw widespread expansion during the 2003 SARS outbreak to address nosocomial transmission in overwhelmed facilities.^[73]^[74] Studies demonstrate the effectiveness of AIIRs in reducing cross-contamination, with systems achieving over 12 air changes per hour capable of decreasing airborne viral particles by up to 99% within 30 minutes.^[75] Integration with complementary measures, such as upper-room ultraviolet (UV) disinfection, enhances containment by inactivating pathogens in residual aerosols, as evidenced in historical TB isolation pilots and modern evaluations.^[76] Overall, these rooms significantly lower transmission risks in healthcare environments when properly maintained.^[77]

Engineering and Industrial Uses

Vacuum Systems

Vacuum systems are engineered setups designed to generate and maintain negative pressure environments by removing gas molecules from an enclosed volume, enabling a range of technological processes. These systems operate across various pressure regimes, from rough vacuum—typically 10 to 100 kPa below atmospheric pressure (approximately 1000 to 1 mbar)—to high vacuum below 1 Pa, and extending to ultra-high vacuum (UHV) at pressures as low as 10^{-9} Pa.^[78]^[79] Rough vacuum systems commonly employ rotary vane pumps, which use rotating vanes in an oil-sealed chamber to displace gas and achieve initial evacuation. These pumps are versatile for applications requiring moderate vacuum levels, such as initial chamber pump-down in industrial setups. For higher vacuums, turbomolecular pumps are utilized, featuring high-speed rotating blades that impart momentum to gas molecules, directing them toward an exhaust, often backed by a roughing pump to handle higher inlet pressures.^[78]^[80] Key components of vacuum systems include pumps, valves for isolating sections or controlling flow, and traps to capture contaminants like vapors or particulates, preventing backstreaming into the main chamber. Oil-free diaphragm pumps, which flex a diaphragm to create alternating compression and expansion without lubricants, are preferred in clean environments to avoid contamination. Pressure ranges span from low vacuum in household devices (around 10 kPa below atmospheric) to UHV systems achieving 10^{-9} Pa for sensitive experiments. Fluid cavitation risks at pump inlets, where low pressure causes vapor bubble formation and collapse, can damage components and are mitigated by ensuring adequate inlet pressure.^[81]^[82]^[83] The fundamental principle underlying these systems is the progressive removal of gas to reduce molecular density, creating a partial vacuum. This process aligns with the ideal gas law, PV = nRT, where for a fixed amount of gas (n) and temperature (T), pressure (P) and volume (V) are inversely proportional, illustrating how decreasing n lowers P in a constant-volume chamber.^[84]^[85] In semiconductor manufacturing, vacuum systems maintain controlled negative pressures in chemical vapor deposition (CVD) chambers, often around 100 Pa, to enable uniform thin-film growth without atmospheric interference. Similarly, space simulation facilities, such as NASA's vacuum chambers, replicate orbital conditions at pressures around 10^{-5} Pa using cryopumps and turbomolecular systems to test spacecraft components under simulated vacuum.^[86]^[87] Recent advancements in vacuum technology for quantum computing, as of October 2025, include cryogenic pumps that use supercooled surfaces to adsorb gases, achieving ultra-high vacuum levels around 10^{-7} Pa for ultra-stable, low-noise environments.^[88]

Filtration and Suction Processes

In industrial processes, negative pressure plays a crucial role in suction mechanisms for material handling, particularly through the Venturi effect in pneumatic conveyors. These systems utilize a converging-diverging nozzle to accelerate airflow, creating a low-pressure zone that generates vacuum levels up to -50 kPa to entrain and lift fine powders such as cement or flour over short distances. Similarly, cyclone separators rely on pressure differentials, typically 0.37 to 0.75 kPa, to induce centrifugal forces that separate particulates from gas streams in pneumatic transport lines.^[89] Filtration applications leverage negative pressure to drive separation in various sectors. In factory dust collection, baghouses operate under suction pressures of -2 to -5 kPa to capture airborne particulates on fabric filters, preventing emissions in environments like metalworking or woodworking facilities.^[90] For liquid filtration, vacuum drum filters in breweries apply negative pressure to pull beer through precoat media, removing yeast and haze while maintaining product clarity at typical vacuum levels of 40-60 kPa.^[91] The flow through porous media in these filtration processes is governed by Darcy's law, which quantifies the volumetric flow rate Q as

Q = -\frac{k}{\mu} \nabla P,

where k is the permeability of the medium, \mu is the fluid viscosity, and \nabla P is the pressure gradient—negative in vacuum-driven systems to induce flow from high to low pressure regions. Representative examples illustrate these applications in specialized industries. In mining, slurries from ore processing are dewatered using vacuum filters at approximately -60 kPa to produce drier cakes for tailings management, enhancing water recovery.^[92] In pharmaceutical production, sterile filling lines employ negative pressure isolators to maintain containment during vial or syringe filling, preventing microbial ingress while handling sensitive formulations.^[93] Integrating variable speed drives on vacuum pumps in filtration setups can reduce power consumption by 15-35%, achieved by matching motor speed to varying process demands and minimizing over-pressurization, according to 2024 market analyses.^[94]

Safety and Measurement

Potential Hazards

Negative pressure systems present several physical risks, primarily due to the structural stresses imposed on materials. Vacuum vessels, such as glassware, are particularly susceptible to implosion when subjected to significant negative pressures, potentially leading to violent collapse and the projection of sharp fragments that can cause lacerations or penetrating injuries. For instance, evacuated glass containers may fail spontaneously from internal strain or minor impacts, with implosions reported in laboratory settings under significant vacuum.^[95]^[96] In fluid-handling applications, cavitation within pumps generates high-speed bubble collapses that erode component surfaces, resulting in material loss rates of up to 0.5 mm per year in susceptible installations like hydroelectric turbines or industrial pumps.^[97] Health hazards arise from both direct physiological effects and exposure to airborne contaminants. Unfiltered suction systems in industrial environments, such as mining, can draw in fine particulates like silica dust, facilitating inhalation and leading to silicosis—a progressive lung disease characterized by fibrosis and impaired respiratory function.^[98] In medical contexts, over-application of negative pressure during procedures like nasopharyngeal suctioning can induce barotrauma, causing tissue damage from pressure differentials in the airway or sinuses.^[99] Systemic issues further compound these dangers. Reduced ambient pressure lowers the boiling point of liquids, enabling fluids to vaporize at room temperature under high vacuums approaching full atmospheric pressure (around -100 kPa), which may result in rapid phase changes, equipment flooding from condensed vapors, or loss of process fluids.^[100] In high-vacuum environments, electrical arcing can initiate across electrodes or insulators, generating temperatures exceeding 10,000 K and risking severe burns, equipment meltdown, or plasma-induced failures in precision systems.^[101] Notable incidents underscore these risks. In October 2021, a glass vacuum trap exploded due to over-pressurization during a chemistry experiment at Northwestern University, injuring a researcher with flying debris.^[102] Industrially, a 2003 fire at the BLSR facility in Rosharon, Texas, ignited when flammable hydrocarbon vapors released during vacuum truck unloading into an open pit reached explosive concentrations, engulfing vehicles and personnel in flames.^[103] Basic mitigation involves engineering controls like vacuum relief valves, which are calibrated to activate at approximately 110% of the operating negative pressure, admitting atmospheric air to prevent excessive differentials and structural failure.^[104]

Detection and Monitoring Techniques

Real-time sensors play a crucial role in detecting and monitoring negative pressure in operational settings, ensuring precise measurements across various vacuum levels. Capacitance manometers, such as those developed by MKS Instruments, provide gas-independent absolute pressure readings suitable for negative pressure environments, typically operating in ranges from 0.1 mTorr to 2000 Torr (approximately 0.013 Pa to 266 kPa below atmospheric), with resolutions as fine as 0.01% of full scale for enhanced accuracy in low-pressure regimes.^[105]^[106] For ultra-high vacuum applications, where pressures drop below 10^{-10} Torr, ionization gauges like the Bayard-Alpert type from Agilent offer reliable detection down to 2 × 10^{-11} Torr, ionizing residual gas molecules to measure ion currents proportional to pressure.^[107] Monitoring protocols emphasize continuous data acquisition and automated responses to maintain safety in negative pressure systems. These systems often incorporate continuous logging of pressure data with configurable alarms triggered by deviations, such as a 10% drop from setpoint, to alert operators of potential failures in industrial or medical environments.^[108] Integration with programmable logic controllers (PLCs) enables real-time oversight and automated adjustments, as seen in SCADA-based setups that log pressure trends and coordinate with ventilation controls for seamless operation.^[109] Advanced techniques enhance detection sensitivity for challenging conditions, such as metastable pressures or early cavitation events. Optical interferometry, utilizing fiber-optic Fabry-Pérot sensors, allows non-contact measurement of vacuum pressure by analyzing spectral shifts in interference patterns, achieving high precision for distributed monitoring in complex systems.^[110] Acoustic sensors detect cavitation onset through frequency analysis of emissions, identifying bubble formation via shifts in the 10-15 kHz range, which signals the transition to unstable negative pressure regimes in fluid-handling applications.^[111] Regulatory standards guide the implementation of these techniques to ensure compliance and safety. The Occupational Safety and Health Administration (OSHA) mandates monitoring of airborne infection isolation rooms (AIIRs) with negative pressure, requiring verification of at least 6-12 air changes per hour through regular differential pressure assessments.^[112] For vacuum systems, ISO/TS 27894 specifies leak detection using helium mass spectrometry, where helium tracer gas is introduced to quantify leaks down to 10^{-9} mbar·L/s, integrating with mass spectrometers for precise industrial validation.^[113] Post-2020 upgrades in hospital infrastructure, driven by the COVID-19 pandemic, have incorporated IoT-enabled sensors for remote negative pressure verification, allowing real-time data transmission from isolation rooms to central dashboards and reducing manual interventions during high-risk periods.^[114] These enhancements, often featuring wireless differential pressure monitors, improved response times and compliance in temporary negative pressure setups across global healthcare facilities.

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However, even though we generally do not encounter negative absolute pressures in thermodynamics, any finite tensile stress in a fluid or a solid is ...
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Aug 6, 2025 · In this paper we show that any condensed phase can exist in absolute negative pressure regimes, while the same is not true for gas phases.
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While the pressure of all familiar kinds and states of matter is non- negative, various models do predict negative pressures in some exotic states.
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May 4, 2020 · The deviation between the model and experimental pressures is less than 3% at positive pressure and 1 MPa at negative pressure. FIG. 5 ...
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[PDF] Exploring water and other liquids at negative pressure
To generate negative pressure, Meyer used a technique designed by Berthelot in 1850 [18]. A glass container is nearly filled with water and sealed.
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Xylem anatomical adjustments prioritize hydraulic efficiency over ...
Jun 15, 2018 · The xylem pressure at 50% loss of hydraulic conductance (P50) varied across trees from −3.28 MPa to −5.98 MPa (H from 2 to 37 m), with overall ...
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Bernoulli's Equation - NASA Glenn Research Center
The equation states that the static pressure ps in the flow plus the dynamic pressure, one half of the density r times the velocity V squared, is equal to a ...Missing: negative | Show results with:negative
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Fluid Dynamics | Harvard Natural Sciences Lecture Demonstrations
Bernoulli's Principle states that the pressure exerted by a fluid is velocity dependent; the faster the velocity the lower the pressure. This can be ...
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Vapor Pressure of Water
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[PDF] Cavitation - MIT
Cavitation is defined as the process of formation of the vapor phase of a liquid when it is subjected to re- duced pressures at constant ambient temperature.
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C-SAMBA Optical Cavitation
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On the Applicability of Cavitation Erosion Risk Models With a ...
Cavitation erosion can cause severe damage to the propeller blades, and gives opposite design trends to fuel efficiency, rendering cavitation erosion risk ...
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[PDF] NUMERICAL STUDY ON CAVITATION EROSION RISK OF MARINE ...
The boundary layer downstream of the propeller was obtained and low negative pressure at the tip vortex core was confirmed. Axial velocity, tangential ...
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[PDF] Hydraulic Pumps
Net Positive Suction Head (NPSH). ▫ On the suction side of a pump, low pressures are very common. Check for cavitation (Vapor pressure).
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- Pump cavitation performance is generally pre- sented in terms of the net positive suction head (NPSH) required at a specified ratio of the head-rise ...
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Physiologic Effects of Negative Pressure Ventilation in Acute Exacerbation of Chronic Obstructive Pulmonary Disease | American Journal of Respiratory and Critical Care Medicine
### Summary of Pressure Levels, Principles, and Efficacy in Respiratory Failure
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The Iron Lung | Science Museum
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Negative Pressure Ventilation - Virtual Museum
The inventor of the 1914 device did not file for a patent. ... Dr. Philip Drinker and Dr. Louis A. Shaw developed an early negative pressure respirator. A patent ...
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Negative-pressure ventilation: is there still a role? - ERS Publications
This difference can be generated by negative pressure in the pleural space, by positive pressure applied to the airway opening, or by a combination of both.
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May 6, 2022 · 1 ALS patient avoided EI, 3 ALS patients slowed pulmonary deterioration, 2 DMD patients were weaned from PPV ... negative pressure ventilation in ...
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Oct 16, 2025 · Applying a negative-pressure Cuirass device in combination with positive pressure ventilation (PPV) improved her carbon dioxide clearance ...
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Negative Pressure Wound Therapy: Mechanism of Action and ... - NIH
Negative pressure wound therapy (NPWT) promotes healing by evenly applying negative pressure on the surface of the wound.
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Jan 2, 2025 · NPWT involves the placement of a well-sealed foam dressing and the application of sub-atmospheric pressure to help reduce inflammatory ...
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Topical Negative Pressure Wound Dressing and Its Applications in ...
This article explores the technique of negative pressure wound dressing, the theories pertaining to mechanism of action, and the increasingly broad indications ...
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The Evolution of Commercial Negative Pressure Wound Therapy ...
The first commercially available NPWTi system was introduced in 2002 (V.A.C. Instill® Therapy Unit, KCI), and initial studies showed reduced bacterial loads ...
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Effect of negative pressure wound therapy on wound healing
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Negative pressure wound therapy: past, present and future - PMC
Negative pressure wound therapy (NPWT), which was introduced as a commercial product (V.A.C.® Therapy, KCI USA, Inc., San Antonio, TX) less than 20 years ago, ...
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The Application of Negative Pressure Wound Therapy in the ... - NIH
The treatment requires a vacuum source to create a continuous or intermittent form of negative pressure inside the wound. Doing so removes fluid and exudates ...
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Nursing Pocket Card | Guide to Negative Pressure Wound Therapy
Jan 28, 2025 · Negative pressure application creates movement of fluid through cellular matrix creating shear and deformation forces on cells promoting ...
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Full article: Using portable negative pressure wound therapy ...
Dec 9, 2014 · Mechanism of action. Subatmospheric pressure improves the wound environment, accelerating healing and reducing wound closure time. Animal ...
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[PDF] Negative Pressure Wound Therapy | Kaiser Permanente Washington
A vacuum pump connected to the draining tube(s) in the wound dressing is used to apply pressure to the wound surface in the range of -50 to -125 mmHg. The ...
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Negative pressure wound therapy: Regulating blood flow perfusion ...
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Influence of advanced wound matrices on observed vacuum ...
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[PDF] EWMA DOCUMENT: NEGATIVE PRESSURE WOUND THERAPY
Oedema. An experimental study in pigs indicated an effect by NPWT over closed incisions in oedema. The results from studying how radiolabel microspheres are ...
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[PDF] An Algorithmic Approach to Negative Pressure Wound Therapy
Reduction of edema. – Promotion of perfusion to the wound bed. 3) Reduces edema. 1) Draws wound edges together. 2) Removes infectious material. 4) Promotes ...<|separator|>
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Negative-Pressure Wound Therapy in Diabetic Foot Management
NPWT increased the likelihood of complete DFU healing at 12–16 weeks by ~45% and shortened time to healing by ~2–3 weeks. Single-use, ultraportable NPWT devices ...
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Comparison and evaluation of negative pressure wound therapy ...
May 15, 2025 · At the 4-week assessment, the NPWT group exhibited significantly higher mean percentage reduction in wound area (35.01% vs. 32.53%, P = 0.033) ...
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Evaluation of the Role of Negative Pressure Wound Therapy (NBWT ...
Aug 23, 2023 · To evaluate the role and the effectiveness of (NBWT) in the healing of diabetic foot ulcers (DFU), and to compare the rate of healing and the ...
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The effect of negative pressure wound therapy on the outcome of ...
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Efficacy and safety of negative pressure wound therapy for the ... - NIH
Meta-analysis demonstrated a significant improvement in wound healing rate [risk ratio (RR) = 1.46, 95%CI: 1.22-1.76, P < 0.01] and a reduction in amputation ...
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[PDF] Airborne Infection Isolation Rooms
Dec 7, 2023 · AIRBORNE INFECTION ISOLATION ROOMS (AIIRs). 6. • CDC and ASHRAE guidelines recommend a negative pressure differential of at least 0.01 "w.g. ...Missing: 2024 | Show results with:2024<|separator|>
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HEPA Air Filters Serve Critical Function in Containing Pathogens ...
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Oct 23, 2023 · Recommendations in this guideline largely address infection prevention strategies available to frontline. 77 healthcare personnel (HCP) at the ...
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C. Air | Infection Control - CDC
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Transmission-Based Precautions | Infection Control - CDC
Ensure appropriate patient placement in an airborne infection isolation room (AIIR) constructed according to the Guideline for Isolation Precautions. In ...Missing: negative | Show results with:negative
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Purpose. 1. Reduce the risk of patient and staff airborne exposure to communicable diseases in the operating room (OR) theatre during surgical procedures.<|separator|>
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engineering controls (in particular, negative-pressure ventilation of isolation rooms for patients with infectious tuberculosis), and ... 1970s. States and ...
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Severe Acute Respiratory Syndrome (SARS): Lessons for Future ...
For any future outbreaks of SARS or similar respiratory illness, it will be imperative to isolate hospitalized patients in negative pressure rooms, which draw ...
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TRAINERWALL: An Innovative, Cost-Effective Removable Anteroom ...
[12] demonstrated that negative pressure rooms operating at >12 ACH effectively reduced airborne viral particles by 99% within 30 min. These findings ...
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Modeling studies and observational evidence show that increasing ventilation and air cleaning can reduce the amount of virus in the air and potentially reduce ...
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Today the rotary vane pump is one of the most commonly used vacuum pumps. A rotary vane pump is shown in Figure 4.9. The rotary vane pump works on the same ...
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Understand the working principle of turbomolecular pumps, with explanatory diagrams and an introduction to operational best practices.
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Turbomolecular vacuum pumps require a backing pump to function properly since they cannot operate at atmospheric pressure. To provide a convenient solution, ...
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Diaphragm Vacuum Pump
Clean Operation (Oil-Free): Diaphragm pumps create a contamination-free vacuum environment by operating without oil, ensuring uncontaminated samples and ...
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A vacuum system consists of a volume, the chamber, connected to a vacuum pump. The vacuum pump is the active mechanism used to remove gases from the chamber.
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Vacuum Pressure Control for Semiconductor Fabrication
A Baratron capacitance manometer senses pressure in a vacuum chamber; This pressure is compared to the desired set point pressure in the pressure controller ...Vacuum/pressure Control... · Downstream Valves And... · Upstream Valves And Pressure...
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Space Environment Simulator
... chamber pressure below 100 microns (0.1 Torr). Once the initial pumpdown is complete, the high vacuum pumping system, consisting of 8 cryopumps and a ...
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Cyclone Dust Collectors - Nederman MikroPul
Large diameter cyclones can efficiently handle high dust loads (114.4 to 218.8 g/m³ ( 50-100 grains per cu.ft)) with low pressure drops (0.37 to 0.75kPa (1.5 to ...
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[PDF] Chapter 1 Section 6 - Baghouse and Filters - EPA
negative pressure in the suction baghouse can result in outside air infiltration, which can result in condensation, corrosion, or even explosions if ...
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Rotary vacuum filter - VLS Technologies
VLS Technologies' rotary vacuum filter is conceived and realized to filter a wide range of beverage products and food liquid.Frs 2-5 · Product Used For · Shoreline Fruit And Vls...
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FLSmidth filter implemented at new copper mine
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Esco Pharma's prized isolation technology can be configured at either positive or negative pressure with a unidirectional/laminar recirculating or total ...
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Pressure and Vacuum Systems - Princeton EHS
Vacuum work can result in an implosion and the possible hazards of flying glass, splattering chemicals and fire. All vacuum operations must be set up and ...High Pressure Vessels · Vacuum Apparatus · Glass Vessels
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Research on synergistic erosion by cavitation and sediment: A review
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Online calculator, figures and tables giving the boiling temperatures of water in varying vacuum, SI and Imperial units.
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Direct observation of vacuum arc evolution with nanosecond ...
Vacuum arcs are particularly detrimental for high precision devices that are built to employ high electric and electromagnetic fields. Amongst these are multi- ...
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Lessons Learned: Vacuum Trap Explosion at Northwestern
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Sep 17, 2003 · The fire was caused by the release of hydrocarbon vapor during the unloading of BS&W from two vacuum trucks into an open area collection pit.
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Pressure Vacuum Relief Valves (PVRV) protect assets and reduce emissions. Types include weight-loaded, spring-loaded, and 10% overpressure protection. Weight- ...Discover The Animation Of A... · Read The White Paper · BrandsMissing: mitigation | Show results with:mitigation
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Baratron Capacitance Manometers - MKS Instruments
Baratron capacitance manometers are usually stand-alone transducers typically requiring a ±15 volt power supply and deliver a 0-10 volt pressure signal.
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Capacitance Manometers - INFICON
INFICON Capacitance Manometers deliver precise and stable pressure measurements across a wide range from 0.1 mTorr to 2000 Torr.
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The simplest way to monitor a negative pressure room is with a room pressure monitor (RPM). RPMs can produce visual and/or audible alarms to notify staff if the ...Missing: protocols PLC
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[PDF] Design and Implementation of PLC and SCADA based Monitoring ...
The networking and data-logging capability of the PLC ensures remote monitoring of critical by plant operators.
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Vacuum pressure imaging solution based on fiber-optic Fabry-Pérot ...
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Cavitation detection in hydraulic machinery by analyzing acoustic ...
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Positive & Negative Pressure Room Monitoring For Hospitals
Sep 13, 2020 · Isolation rooms sometimes use negative air pressure to prevent airflow of infected air. Negative pressure helps prevent airborne diseases (such as Covid-19) ...