Discharge is where an LEV system begins to interact with the building, neighbouring work areas and the external environment. Outlet position, discharge direction, air treatment and recirculation determine whether captured material can return to occupied space. This page treats those matters as engineering features of LEV plant, excluding personal exposure monitoring, health-effects assessment and airborne contaminant sampling. Related subjects are addressed separately by the respirable crystalline silica site, the industrial hygiene site's page on ventilation and LEV assessment, the VOC and indoor chemicals site's coverage of adhesives, sealants and solvents, the construction dust site and the duct hygiene sibling dealing with kitchen extract cleaning.
ADPHC Code of Practice CoP 52.0 Local Exhaust Ventilation, Version 4.1, dated 27 February 2026, is issued by the Abu Dhabi Public Health Centre under ADOSH-SF and is mandatory for employers in the Emirate of Abu Dhabi. Section 3.2(d) states: "Air outlet from every LEV shall be discharged to the outside atmosphere. Systems designed to collect non-hazardous materials (e.g. wood dust) can return air back into the work area as long as it has a filtration system that removes repairable dusts and particles and does not result in a harmful exposure to employees."
The first sentence establishes outside discharge as the default. The second creates a limited route for return to the work area, but only for systems collecting non-hazardous materials, only where a filtration system is present, and only where the returned air does not result in harmful employee exposure. Wood dust is the Code's own example. The permission should not be broadened to hazardous materials or treated as a general energy-saving entitlement.
The printed phrase "repairable dusts" appears exactly that way in CoP 52.0. It is evidently a typographical error for respirable, but no argument about scope, filter performance or contaminant class should be built on the error. The operative controls remain the stated non-hazardous-material limitation, the filtration condition and the requirement that harmful exposure must not result.
CoP 52.0 Section 3.2(g) adds: "Exhausted material shall be subject to regular emissions monitoring where appropriate, and as a minimum where exhaust material may be harmful to the environment." The supplied clause gives no frequency, averaging period, sampling basis, analytical method or emission limit, so "regular" must not become an invented interval.
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, not federal law. Its stated position is stricter than the Abu Dhabi rule because it gives no exception for return of filtered air carrying non-hazardous material. The Dubai modal is "should", whereas the Abu Dhabi sentence directing discharge outside uses "shall".
In the Emirate of Abu Dhabi, ADPHC CoP 52.0 permits return only for non-hazardous materials, with filtration, and where no harmful employee exposure results. In Dubai, the supplied Dubai Municipality technical guideline says LEV air should not be recirculated into the workroom. The sources therefore do not express one uniform position.
Sharjah Guideline OSHJ-GL-12 Local Exhaust Ventilation, Version 1 Rev 0, September 2021, is issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah. It is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements, not federal law. Section 5.5.6 states: "Should air be re-circulated directly back into the workplace, the entity must ensure air is sufficiently cleaned so as not to present a risk to employees in the workplace".
Sharjah therefore takes a third formulation. It contemplates direct recirculation but makes sufficient cleaning and absence of workplace risk the controlling conditions. The supplied Sharjah text does not define a filtration class, contaminant limit, test method or verification frequency for "sufficiently cleaned". Those details must not be invented. The design record should instead show how the selected cleaning arrangement addresses the actual material and how the entity concludes that recirculation does not present the stated risk.
ADPHC CoP 52.0 Section 3.2(e) states: "Exhausts of LEV shall not be located in an area that will expose other employees or near air intakes for building ventilation and/or climate control systems." The clause addresses both direct exposure near the outlet and re-entry through building systems. It does not state a general separation distance in Section 3.2(e), so no universal dimension should be attached to this rule.
Sharjah OSHJ-GL-12 Section 5.5.6 says discharge should avoid air re-entering the building and should not discharge into air inlets. It also says the outlet should be at an appropriate height for dispersal and should have an appropriate termination to ensure efficient airflow, prevent rainwater ingress and assist fume dispersal. The supplied Guideline does not define "appropriate height" with one dimension or prescribe one termination design for every LEV system.
Outlet design concerns the airflow path, not merely an opening through an external wall. Roof shape, parapets, nearby structures, air intakes and discharge direction may influence whether exhaust is carried away or returned. The sources supply no dispersion calculation or wind-study method. A termination must preserve the intended path rather than preventing rain ingress by turning exhaust towards the roof.
A second Abu Dhabi clause sits outside the LEV Code. ADPHC Code of Practice CoP 8.0 General Workplace Amenities, Version 4.0, dated 15 July 2024, is an amenities Code issued by the Abu Dhabi Public Health Centre under ADOSH-SF and is mandatory for employers in the Emirate of Abu Dhabi. Section 3.7(d) states: "Fresh air intakes for HVAC systems shall be located in a place that shall not pull in environmental contaminates such as vehicle exhaust, noxious fumes, unpleasant smells, or chemical contaminants."
CoP 8.0 is not an LEV instrument. Its intake clause and CoP 52.0 Section 3.2(e) sit in two different Codes. Read together, however, they create a two-sided re-entrainment rule in Abu Dhabi: the LEV outlet must not be near building ventilation or climate-control intakes, and the building fresh-air intake must not be positioned so that it draws in exhaust, fumes, smells or chemical contaminants.
The two clauses place design attention on both sides of the air path. Moving an LEV stack without examining the HVAC intake may leave the problem unresolved, while relocating an intake without considering the discharge plume may do the same. Neither supplied clause gives a universal separation distance for this general relationship. The engineering record should therefore show how outlet and intake locations were considered together.
ADPHC CoP 52.0 Section 3.4(d) contains specific stack provisions for fume hoods. It requires stacks to be at least two metres above the roof and one metre above any parapet walls, whichever is greater. Two metres and one metre are heights, not measured quantities, and therefore have no averaging period or sampling basis.
The same section specifies a minimum of 15 metres and preferably a downwind location from any air intakes. Fifteen metres is a distance, not a measured quantity, and therefore has no averaging period or sampling basis. The Code adds: "This distance can be increased as needed to prevent re-entrainment of exhaust fumes". The stated minimum is therefore not presented as an automatic guarantee against re-entrainment.
Section 3.4(d) also states that "rain caps and other such devices are not allowed if they divert the exhaust towards the roof". The restriction is conditional on the effect of the device. It does not say that every form of weather protection is prohibited, but it prevents a termination from solving rain ingress by directing contaminated exhaust back towards the roof.
These dimensions belong to the fume hood stack provisions in Section 3.4(d) and must not be extended to every LEV outlet. The broader Abu Dhabi and Sharjah siting rules provide no universal stack height or separation distance for other systems.
ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi. Dubai Municipality Technical Guidelines are Dubai Municipality technical guidelines, and Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah.
ADPHC CoP 52.0 Sections 3.2(e), 3.2(g) and 3.4(d); ADPHC CoP 8.0 Version 4.0 dated 15 July 2024; Dubai Municipality DM-HSD-GU43-SUOS2 V4.0; Sharjah OSHJ-GL-12 Section 5.5.6.
ADPHC Code of Practice CoP 52.0 Local Exhaust Ventilation, Version 4.1, dated 27 February 2026, is mandatory for employers in the Emirate of Abu Dhabi under ADOSH-SF. Section 3.2(d) requires the air outlet from every LEV to discharge to the outside atmosphere, but permits systems collecting non-hazardous materials, with wood dust given as the example, to return air to the work area where filtration is provided and harmful employee exposure does not result. The printed phrase "repairable dusts" is evidently a typographical error for respirable and should not support any technical argument. The permission is limited and does not apply generally to hazardous materials.
Dubai Municipality DM-HSD-GU43-SUOS2 Technical Guidelines for Safe Use of Industrial Organic Solvents V4.0 is a Dubai Municipality technical guideline, not federal law, and states: "Air from local exhaust ventilation system should not be re-circulated into the workroom". That "should" position allows no stated exception in the supplied Dubai text. By contrast, ADPHC CoP 52.0 is mandatory for employers in the Emirate of Abu Dhabi under ADOSH-SF and uses "shall" for outside discharge while permitting return for non-hazardous materials only where filtration is present and harmful exposure does not result. The two sources therefore express materially different approaches.
Sharjah Guideline OSHJ-GL-12 Local Exhaust Ventilation, Version 1 Rev 0, September 2021, is issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah and sets minimum acceptable requirements rather than constituting federal law. Section 5.5.6 states: "Should air be re-circulated directly back into the workplace, the entity must ensure air is sufficiently cleaned so as not to present a risk to employees in the workplace". The supplied Guideline states no filtration class, contaminant limit, test method or verification frequency for that condition. It also says discharge should avoid re-entry into the building and should not be directed into air inlets.
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