Ductwork carries contaminated air from the hood to downstream plant. Its route must preserve enough air movement to prevent settling, resist leakage, allow inspection and cleaning, remain supported and avoid unnecessary resistance. This page addresses ducting as local exhaust ventilation engineering plant and does not cover personal exposure monitoring, health effects or airborne contaminant sampling. Its concern is reliable conveyance through the installed route.
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 5.5.3: "The velocity of the air passing through the ductwork must be sufficient to achieve the required transport velocity and to prevent settling of material. Recommended duct velocities depend on the contaminants being transported." Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in Sharjah; it is not federal law.
Transport velocity concerns movement inside the duct rather than capture outside the hood. Capture brings a release into the inlet, while transport carries it through the connected route. A system can capture at the source yet allow material to settle downstream, so both functions must be considered within the same plant. Settlement can progressively narrow the effective passage, alter resistance and create a condition different from the documented design even while the fan continues to run.
The Sharjah Guideline names transport velocity, links it to settlement prevention and says that recommended velocities vary with the contaminant. It publishes no numeric duct velocity for any contaminant and names no averaging period, sampling basis, traverse method, instrument or test point. A general value cannot therefore be presented as a Sharjah requirement, although the duct must still prevent settling.
Section 5.5.3 states that ducting should be of suitable material and "as simple as possible with a minimum number of bends and be as short as possible". It also says that branches should join at the sides at an acute angle. These are qualitative design directions, not numeric velocity criteria.
A long, indirect route creates resistance that the air mover must overcome. Bends and abrupt junctions disturb the flow path and can affect material transport. They also create locations where deposits and wear may be harder to identify or remove. An acute branch entry avoids arranging the connection as a blunt collision between air streams. The source prescribes no angle, branch ratio, maximum overall length or maximum number of bends, so none can be presented as a Sharjah requirement.
The Sharjah Guideline also says that flexible ducting should be kept to a minimum because it wears more quickly and offers higher resistance to airflow. It does not prohibit every flexible connection or state a maximum flexible length. Wear, deformation and route changes can alter resistance, but the source publishes no inspection interval for flexible ducting.
The same section states that noise should be minimised at the design stage. This places noise within initial system arrangement rather than treating it only as a later maintenance concern. The supplied material contains no numeric noise criterion for this provision.
Sharjah OSHJ-GL-12 states that adequate inspection hatches should be "placed at the top of the ducting". That position is a design instruction rather than a measured quantity, so no averaging period or sampling basis applies. The source publishes no general hatch spacing, hatch size or cleaning frequency.
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(j) that inspection or clean-out doors must not exceed 4 metres of running length. Four metres is a distance, not a measured air quantity, and no averaging period or sampling basis applies. ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi; they are not federal law.
Section 3.2(k) requires a clean-out door for servicing the fan and, where necessary, a drain. These provisions make access part of the installed plant rather than an improvised response after blockage or fan failure. The Code states no cleaning frequency, purge period or door dimension in the supplied material.
Sharjah provides a top-positioned hatch direction without general spacing, while Abu Dhabi provides maximum running-length spacing and separate fan-service access. Neither source states that access alone proves adequate transport velocity or effective cleaning. The openings must still correspond with the actual route and components that require inspection, but the supplied material gives no further layout formula.
ADPHC CoP 52.0 Section 3.2(l) requires ductwork to be supported throughout its length so that it sustains its own weight, normal internal contaminant accumulation and any negative pressure exerted during operation. The clause recognises deposited material and pressure as structural loads but publishes no support spacing or design pressure.
Section 3.2(m) requires joints and seams to be sealed to prevent contaminant loss during use and contamination of other work areas. Leakage can therefore release conveyed material and reduce airflow available elsewhere in the network. A visually complete duct route is not functionally complete if its joints cannot retain the extracted stream.
Section 3.2(n) requires protection by open space or fire-resistive material where ductwork penetrates a combustible roof or wall. Section 3.2(o) states that ductwork must not pass through firewalls unless no practicable alternative exists, when an assessment must identify the risks. These are requirements of an ADPHC Code mandatory for employers in the Emirate of Abu Dhabi, not federal law.
The supplied material states no penetration dimensions, fire-resistance periods or prescribed assessment form. Those gaps cannot be filled from external practice and described as CoP 52.0 requirements.
The only UAE duct-velocity figure located in the supplied material appears in ADPHC CoP 52.0 Section 3.5.2(c): "a recommended minimum duct velocity of 4,500 feet per minute in the branch and 3,500 feet per minute in the main". The source states no averaging period, sampling basis, traverse method, measuring instrument or test point for either value.
Every limit on that sentence matters. The Code uses "recommended", not "shall". The passage sits within the grinding, polishing and buffing section and applies only to grinding-wheel ventilation systems. It carries no measurement condition. It names no instrument and no test point.
The values therefore cannot be generalised to welding, mixing, transfer, vapour control or any other process. ADPHC CoP 52.0 is mandatory for employers in the Emirate of Abu Dhabi, but the recommendation remains confined by its wording and location. Sharjah OSHJ-GL-12 says recommended duct velocities depend on the contaminant yet supplies no figures.
Dubai Municipality Technical Guidelines are Dubai Municipality technical guidelines, and Trakhees Regulation IO-4.0 applies in Trakhees jurisdictional areas; neither is federal law. No quoted general duct-velocity requirement from either source has been supplied, so none is added.
Duct design decisions should remain identifiable in system records because later inspection depends on knowing the intended route, branch arrangement, clean-out access and supported condition. The supplied UAE passages do not prescribe a record format, retention period or replacement age for ductwork. Silence on those details must be stated rather than replaced with an imported rule.
Replacement becomes an engineering question when the installed duct can no longer preserve the required function through maintenance. Wear in flexible sections, failed joints, damaged supports, inaccessible deposits or unauthorised route changes can each affect performance. Repair may restore some defects, but the supplied material does not define a repair-versus-replacement threshold. It gives no automatic replacement interval, so condition and ability to meet the stated duties remain the relevant considerations.
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.
ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi. 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(j) to 3.2(o) and 3.5.2(c); Sharjah OSHJ-GL-12 Section 5.5.3.
No. Sharjah OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority as a Guideline setting minimum acceptable requirements in Sharjah, states that duct velocity must achieve transport velocity, prevent settling and reflect the contaminant, but it publishes no numeric value. It also names no averaging period, sampling basis, traverse method, instrument or test point. 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, contains a confined grinding-wheel recommendation but no general table; neither source is federal law.
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, describes 4,500 feet per minute in a branch and 3,500 feet per minute in a main as recommended minimum velocities only for grinding-wheel ventilation systems within its grinding, polishing and buffing section. The source states no averaging period, sampling basis, traverse method, instrument or test point. Sharjah OSHJ-GL-12, a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in Sharjah, says recommended velocities depend on the contaminant but publishes no figures; neither instrument is federal law.
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 inspection or clean-out doors at running-length intervals not exceeding 4 metres and a clean-out door for servicing the fan, with a drain where necessary. Four metres is a distance rather than a measured air quantity, so no averaging period or sampling basis applies. Sharjah OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority as a Guideline setting minimum acceptable requirements in Sharjah, directs adequate inspection hatches to the top of ducting but gives no general spacing or cleaning frequency; 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.