Local exhaust ventilation is engineering plant arranged to capture airborne contaminants close to the place where they are generated and carry them through a connected system for treatment and discharge. It is not simply a fan, an open window or general room ventilation. The plant works as a chain whose performance depends on the relationship between the hood or inlet, the ducting, the air cleaner, the air mover and the discharge. A weakness in one element can prevent the complete installation from delivering the intended source control.
Sharjah OSHJ-GL-12 Local Exhaust Ventilation, issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah, uses this component structure across Sections 5.5.1 to 5.5.6. The sequence begins with the hood or inlet, continues through the ducting and air cleaner, passes through the air mover, and ends at the discharge. Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah, not a federal instrument.
The hood or inlet receives the contaminant-laden air. Ducting provides the route through the system. The air cleaner removes contaminants where treatment is needed, the air mover creates the airflow, and the discharge releases the treated or conveyed air at the end of the system. These parts should not be treated as independent accessories because changes to resistance, leakage, blockage, fan duty or discharge arrangement can alter performance elsewhere in the plant.
ADPHC CoP 52.0 supports the same whole-system view. Section 3.2(c) states: "Exhaust fans, jets, ducts, hoods, separators, and all necessary equipment, including refuse receptacles, shall be designed, constructed, maintained and operated as to ensure the required protection by maintaining volume and velocity of exhaust air sufficient to gather dust, fumes, vapors or gases from equipment or processes." ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi. The clause links design, construction, maintenance and operation to sufficient exhaust volume and velocity without publishing one universal value.
ADPHC CoP 52.0 Section 1(b) states: "This CoP sets requirements on how to control gas, vapour, dust, fume and mist in workplace air using local exhaust ventilation (LEV) to extract contaminants before they enter employee's breathing zones." The wording identifies source capture before entry into the breathing zone as the basic purpose. It does not describe LEV as a method for measuring exposure, diagnosing health effects or sampling airborne contaminants.
The Code defines the breathing zone as "The region around operators from which they draw air for breathing. Commonly defined as being within 300 mm of nose/mouth". The 300 mm dimension is a defined distance and not a measured quantity, so it carries no averaging period or sampling basis. The definition matters because it explains the engineering objective: contaminants should be intercepted before they disperse into the region from which breathing air is drawn.
That objective makes hood position and process relationship central. A system can move a substantial volume of air and still fail if the inlet is too far from the release, obstructed by the workpiece or placed where process motion carries the contaminant away from it. Source capture is therefore a design arrangement, not merely evidence that a fan is running.
ADPHC CoP 52.0 defines an air cleaner or arrestor as "A device to remove contaminants from air (e.g. filters, cyclone, sock, wet scrubber, electrostatic precipitator (EP))". The examples show that air cleaning is a functional stage rather than one single technology. Selection depends on the contaminant and process, but the supplied Abu Dhabi text does not create a general replacement period, cleaning frequency or efficiency value for every air-cleaning device.
The air mover supplies the pressure difference that drives flow through the hood, ducts, cleaner and discharge. Its operating point is influenced by the resistance of the connected system. A fan cannot be assessed in isolation from blocked filters, damaged ductwork, altered branches, closed dampers or changes made at the hood. The plant must be understood as one air path.
The discharge is the final connected element. Its arrangement affects where conveyed air is released and whether contaminants can return to occupied space. Dubai Municipality DM-HSD-GU43-SUOS2 Technical Guidelines for Safe Use of Industrial Organic Solvents V4.0 states: "Air from local exhaust ventilation system should not be re-circulated into the workroom". This is a Dubai Municipality technical guideline using the modal "should", and it applies within its stated Dubai scope rather than as a federal rule.
Local exhaust ventilation acts close to the source. General or dilution ventilation changes air within a larger room or space after contaminants have entered it. The distinction is important because the two approaches do not offer the same degree of control over a concentrated release. An installation that merely increases room air movement should not automatically be described as LEV.
Dubai Municipality DM-HSD-GU43-SUOS2 states: "General ventilation and dilution ventilation are not as effective as local exhaust ventilation for the control of atmospheric contaminants. They may be useful to control minor contaminant emissions of low toxicity". This is the only located Dubai text explicitly stating the LEV-over-dilution principle. It appears in a Dubai Municipality technical guideline whose surrounding bullets use "should", so it should not be transformed into a universal numeric design rule or a federal requirement.
The statement also identifies a limited role for dilution ventilation. It may assist with minor emissions of low toxicity, but the source does not publish a boundary value that separates minor from major emissions. No invented concentration, room-air-change rate or toxicity threshold should be added to fill that silence.
Sharjah OSHJ-GL-12 warns against designing around the idea that vapours or dust simply fall because the parent material is dense. Section 5.4 states: "Low-level LEV is often, but mistakenly, applied to control exposure to 'heavy vapours'. In practice, such controls will fail to control exposure". It also states: "Particle aerodynamic size, not simply the density of the parent material, determines how particles move in the air. Dense materials do not produce 'heavy dust' and therefore LEV hoods placed at floor level do not work."
The Sharjah Guideline gives particle size ranges in Table 1. Inhalable dust is listed as 0.01 to 100 micrometres, respirable dust as below 10 micrometres, fume as 0.001 to 1 micrometre, and mist as 0.01 to 100 micrometres. These are size ranges published by the Sharjah Guideline; the source states no measurement condition or sampling basis for them. The table describes categories rather than prescribing capture, face or transport velocity values.
Sharjah OSHJ-GL-12 also states: "Respirable dust clouds are practically invisible at concentrations up to tens of mg/m3". The source gives no averaging period, measurement condition or sampling basis for that statement. The practical implication is that visibility cannot serve as a dependable indicator of whether the plant is capturing fine airborne material.
ADPHC CoP 52.0 defines a sash as "A movable glass panel that covers the face area of a fume hood. Sashes can be vertical, horizontal, or a combination of the two." A sash is therefore a movable part of a particular hood arrangement, not a synonym for the whole LEV system. Its position can influence the open face and airflow pattern, but the supplied general definition gives no universal operating height or velocity.
Neither ADPHC CoP 52.0 nor Sharjah OSHJ-GL-12 publishes a general capture velocity, general face velocity or general transport velocity value. Both sources discuss volume, velocity and effective capture as engineering concepts, but neither provides one number suitable for every contaminant, hood and process. Process-specific figures elsewhere should not be turned into general values for unrelated installations.
Related subjects are separated across sibling resources: the respirable crystalline silica site, the industrial hygiene site with its occupational-hygiene page on ventilation and LEV assessment, the VOC and indoor chemicals site covering adhesives, sealants and solvents, and the construction dust site. The present subject remains the construction and operation of LEV plant itself, excluding personal exposure monitoring, health effects, airborne contaminant sampling and kitchen extract cleaning.
ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi, while Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah. Dubai Municipality Technical Guidelines are Dubai Municipality technical guidelines issued under Local Order 61 of 1991.
ADPHC CoP 52.0 Sections 1(b) and 3.2(c); Sharjah OSHJ-GL-12 Sections 5.4 and 5.5.1 to 5.5.6; Dubai Municipality DM-HSD-GU43-SUOS2 V4.0.
Sharjah OSHJ-GL-12, a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah, presents LEV through the connected elements: the hood or inlet, ducting, the air cleaner, the air mover and the discharge. ADPHC CoP 52.0, which is mandatory for employers in the Emirate of Abu Dhabi, similarly refers to exhaust fans, jets, ducts, hoods, separators and necessary equipment as a connected protective system. The plant should therefore be understood as an air path whose components affect one another, rather than as a fan alone.
No. Dubai Municipality DM-HSD-GU43-SUOS2 Technical Guidelines for Safe Use of Industrial Organic Solvents V4.0 states that general and dilution ventilation are not as effective as local exhaust ventilation for controlling atmospheric contaminants and may be useful for minor emissions of low toxicity. That is a Dubai Municipality technical guideline using "should" in the surrounding provisions, not a federal law or a general numeric design standard. LEV acts close to a source, while dilution ventilation deals with contaminants after release into a wider space.
Neither ADPHC CoP 52.0 nor Sharjah OSHJ-GL-12 publishes a general capture velocity, general face velocity or general transport velocity value. ADPHC CoP 52.0 is mandatory for employers in the Emirate of Abu Dhabi and requires sufficient exhaust volume and velocity to gather contaminants from equipment or processes. Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements and says different situations require different velocities and solutions. A universal value cannot therefore be taken from either supplied source.
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