Capture depends on the relationship between the extraction inlet, the contaminant source and surrounding air movement. A hood can be connected to a running fan and still fail if it is too far from the release, faces the wrong direction or rests on an incorrect idea about how dust or vapour behaves. This page treats local exhaust ventilation as engineering plant and does not cover personal exposure monitoring, health effects or airborne contaminant sampling. Its concern is whether the inlet can intercept the release.
Sharjah Guideline OSHJ-GL-12 Local Exhaust Ventilation, Version 1 Rev 0, September 2021, issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah, states in Section 5.5.1: "The entity should design the extraction inlet to ensure an effective capture velocity, the speed of airflow in metres per second at the inlet of the LEV, different situations will require different velocities and therefore different solutions." Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in Sharjah; it is not federal law.
The wording makes the inlet and process inseparable. Capture velocity is not presented as a universal property of a fan, duct or hood model. It is the air speed needed at the relevant location to draw a release into the inlet despite process momentum and opposing air movement. A fast-moving tool, a warm plume and a slow release beside an enclosing hood present different design problems. The same nominal inlet can therefore be suitable in one arrangement and ineffective in another, because the source direction, release energy and surrounding currents determine whether air actually crosses into the hood.
ADPHC Code of Practice CoP 52.0 Local Exhaust Ventilation, Version 4.1, dated 27 February 2026, issued by the Abu Dhabi Public Health Centre under ADOSH-SF, states in Section 3.2(c): "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; they are not federal law. CoP 52.0 publishes no value for the required volume and no value for the required velocity.
No UAE authority located publishes a general capture velocity value. The Abu Dhabi Code imposes a performance duty but gives no general figure, while the Sharjah Guideline names the design objective and says that different situations require different solutions. The absence of a number does not make any operating hood adequate; it leaves the plant to be specified, positioned and tested against the actual source.
Section 5.5.1 of the Sharjah Guideline states: "The capture velocity at one duct diameter away from the face of the hood is about one tenth of the face velocity. Therefore, if the hood is wrongly positioned, this will result in virtually no capture of the contaminant." One tenth is a ratio and one duct diameter is a distance; neither is a published velocity value, and no averaging period or sampling basis applies to either. The statement describes the rapid decay of an open inlet's influence outside the hood face.
Face velocity exists at the plane of the opening, where airflow is concentrated through a defined area. Outside that plane, the inlet draws from a widening volume of surrounding space, so velocity falls with distance. Face velocity cannot be assumed to persist through the nearby workplace, and a face measurement does not prove that air at a remote release point moves towards the inlet strongly enough for capture.
The Sharjah Guideline states that a wrongly positioned hood will result in virtually no capture of the contaminant. A system can therefore have a rotating fan, audible airflow and measurable face velocity while achieving almost nothing at the source. Position is part of engineering performance, not a secondary matter left to convenience after installation.
Hood position must follow the release path. Cross-draughts, moving machinery, a workpiece, an operator's body or a temporary screen can redirect or obstruct that path. A documented design position also loses meaning if later work changes place the source beyond the original capture zone. The supplied UAE material publishes no universal maximum hood distance, preferred angle or standard location for general processes, so a fixed rule cannot be imported and presented as a UAE requirement.
Section 5.4 of the Sharjah Guideline identifies and rejects a design error by name: "Low-level LEV is often, but mistakenly, applied to control exposure to 'heavy vapours'. In practice, such controls will fail to control exposure". That statement belongs to Sharjah OSHJ-GL-12, a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in Sharjah, not to a federal instrument.
The rejected assumption treats vapour density as though it alone determines where extraction belongs. Vapour movement is also affected by mixing, process heat, air currents, people, equipment and release momentum. A floor-level inlet can therefore be remote from the actual path even where the vapour has a molecular weight greater than air. It may draw substantial room air while leaving the release to pass through the breathing zone and disperse elsewhere.
The engineering lesson is that the inlet must follow actual or reasonably anticipated movement from the source, not the label heavy vapour. The Sharjah Guideline supplies no low-level capture velocity, no general floor distance and no exception making low extraction an accepted default. A low inlet must still be shown to intercept the release effectively.
The same Sharjah section 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." This is a statement in Sharjah OSHJ-GL-12, which sets minimum acceptable requirements under the Sharjah occupational safety and health system.
Dust behaviour cannot be predicted from the bulk density of stone, metal or another parent material alone. Once generated, particles move according to aerodynamic characteristics and process forces. Fine particles from a dense material can remain within moving air and disperse away from the floor. A floor hood based on the belief that dense dust simply drops can miss the release at a tool, transfer point or other source.
This is another capture-distance failure. The inlet can have airflow while its influence at the generation point is negligible. Dust visible on the floor does not prove that a floor-level hood intercepted the airborne release when it was generated. The Sharjah Guideline publishes no floor-level velocity that cures the error; it rejects the premise and directs the design towards capture where the contaminant is generated.
The term "capture velocity" appears zero times in ADPHC CoP 52.0. It appears three times in Sharjah OSHJ-GL-12 and once in Dubai Municipality DM-HSD-GU42-PSB2 Technical Guidelines for Paint Spray Booths V4.0. Those occurrence counts are document-text counts, not measured quantities, and no averaging period or sampling basis applies.
The only located Dubai use is Section 4-1-2: "Airflow into the booth must be adequate to maintain capture velocity and overcome opposing air currents". Dubai Municipality Technical Guidelines are Dubai Municipality technical guidelines; they are not federal law. The sentence names capture velocity but supplies no figure.
No located UAE instrument states an averaging period, traverse method or measuring instrument for any velocity value, and no authority states a general capture velocity value. None of the four located appearances has a number attached. The sources also do not identify a general test position outside the hood at which capture velocity must be measured. A reader looking for a single UAE capture velocity table will not find one because none is published in the located instruments.
Related material sits on the respirable crystalline silica site, the industrial hygiene site, the VOC and indoor chemicals site, the construction dust site and the duct hygiene sibling; those subjects, including kitchen extract cleaning, are not repeated here.
Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah. ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi, and Dubai Municipality Technical Guidelines are Dubai Municipality technical guidelines.
Sharjah OSHJ-GL-12 Sections 5.4 and 5.5.1; ADPHC CoP 52.0 Section 3.2(c); Dubai Municipality DM-HSD-GU42-PSB2 V4.0 Section 4-1-2.
No. ADPHC CoP 52.0, issued by the Abu Dhabi Public Health Centre under ADOSH-SF and mandatory for employers in the Emirate of Abu Dhabi, requires sufficient exhaust-air volume and velocity but publishes no general capture velocity figure. Sharjah OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority as a Guideline setting minimum acceptable requirements in Sharjah, names capture velocity and states that different situations require different solutions but attaches no number. Dubai Municipality DM-HSD-GU42-PSB2, a Dubai Municipality technical guideline for paint spray booths, requires airflow adequate to maintain capture velocity but also supplies no figure; none of these instruments is federal law.
No. Sharjah OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority as a Guideline setting minimum acceptable requirements in Sharjah, states that capture velocity at one duct diameter from the hood face is about one tenth of face velocity. One tenth is a ratio and one duct diameter is a distance, not a velocity value, so no averaging period or sampling basis applies. The same Sharjah section states that wrong hood positioning can result in virtually no capture, while ADPHC CoP 52.0, mandatory for employers in the Emirate of Abu Dhabi under the Abu Dhabi Public Health Centre's ADOSH-SF framework, requires sufficient volume and velocity without publishing a numeric value; neither instrument is federal law.
Not as a default based on those labels. Sharjah OSHJ-GL-12, a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in Sharjah, states that low-level extraction for "heavy vapours" will fail in practice and that dense parent materials do not produce "heavy dust" whose control is achieved by floor-level hoods. The Guideline directs attention to actual vapour movement and particle aerodynamic size, while ADPHC CoP 52.0, issued by the Abu Dhabi Public Health Centre and mandatory for employers in the Emirate of Abu Dhabi, requires hoods and associated plant to maintain sufficient volume and velocity to gather contaminants but publishes no general capture value; neither source is federal law.
Not affiliated with, endorsed by or acting on behalf of the Abu Dhabi Public Health Centre, the Sharjah Prevention and Safety Authority, Dubai Municipality, Trakhees or any other authority or standards body. Any codes, guidelines, schemes or trademarks named are the property of their respective owners.