LEV systems can move away from their intended performance even when no single dramatic failure occurs. Duct damage, deposits, loaded filters, altered dampers, worn fans, deteriorated flexible connections, insufficient make-up air, displaced hoods and inaccessible clean-out points can combine to reduce extraction. UAE sources do not publish universal numerical fault triggers for these conditions. The available engineering tests are condition, functional behaviour and comparison with the system's own design and manufacturer specifications. The boundaries of this engineering-plant resource are distinct from the respirable crystalline silica site, the industrial hygiene site carrying a page on ventilation and LEV assessment from the occupational hygiene angle, the VOC and indoor chemicals site covering adhesives, sealants and solvents, and the construction dust site. Personal exposure monitoring, health effects and airborne contaminant sampling fall outside this site, while kitchen extract cleaning belongs to the separate duct hygiene resource.
Sharjah Guideline OSHJ-GL-12 Local Exhaust Ventilation, Version 1 Rev 0, September 2021, was issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah and sets minimum acceptable requirements. Section 5.6.1 gives a visual-inspection checklist under which the entity should determine whether "LEV hoods are in good condition; Air is being effectively drawn into the extract booth; Any safety or warning devices are operational; Ducting is intact without holes or splits; The area is reasonably clean and contaminant free. The check is generally undertaken by the operator and should be recorded."
This checklist treats visible condition and observable function as routine indicators of plant health. Damage to a hood, weak inward movement at a booth, a failed warning device, holes in ductwork or unusual contamination around the system may indicate that performance has deteriorated. The operator's check does not replace technical measurements, but it may identify changes between formal tests.
The Sharjah Guideline gives no numerical leakage rate, defect size or contamination threshold for this visual check. It states no measurement condition for deciding whether a hole or split is acceptable because no permissible value is provided. Ducting is expected to be intact, and an observed loss of integrity should therefore be investigated against the system's intended condition.
Holes and splits can reduce conveyed airflow, admit unwanted air and allow contaminants to escape before reaching the air cleaner or discharge. Their effect depends on location, system pressure and the extent of damage, but no UAE authority located publishes a permissible leakage rate for LEV ducting. The relevant expectation is intact construction and performance consistent with the system specification.
ADPHC Code of Practice CoP 52.0 Local Exhaust Ventilation, Version 4.1, dated 27 February 2026, was 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(m) states: "Joints and seams shall be sealed to prevent loss of contaminants during use and prevent contamination of other work areas." A failed joint or open seam breaches that expressed duty even if no numerical leakage test has been specified.
Section 3.2(l) states: "LEV ductwork shall be appropriately supported though its length to sustain its weight plus any normal accumulation of contaminants in the interior during normal operating conditions and any negative pressure exerted upon it." This wording recognises that internal accumulation may occur and that the support system must withstand the resulting load. Sagging, movement or separation can therefore be both a structural fault and an airflow fault.
Sharjah OSHJ-GL-12 Section 5.5.3 states: "The velocity of the air passing through the ductwork must be sufficient to achieve the required transport velocity and to prevent settling of material". When transport velocity is lost, particulate matter may settle inside horizontal runs, bends, enlargements or poorly balanced branches. The deposit then reduces the effective duct area and adds resistance, which may further reduce airflow and encourage more deposition.
The Guideline does not publish one universal transport velocity for every substance, duct or process. It also does not provide a numerical depth of settled material that triggers failure. Assessment must therefore use the required transport velocity for the particular system and compare present condition with the design documentation, manufacturer information and established test points.
A settled deposit may also explain why a hood appears weak even when the fan is operating. The restriction may lie several metres away from the hood, particularly where duct routing contains bends, long flexible sections or poorly accessible branches. Observation at the hood should therefore be connected with pressure and velocity measurements throughout the system rather than treated as a complete diagnosis.
As an air cleaner loads, its resistance may rise and the volume of air moved through the connected system may fall. The effect can appear gradually, leaving the fan running and the hood visibly intact while performance drifts below its design condition. No UAE authority located publishes a maximum filter pressure drop for LEV generally. The applicable comparison remains the air-cleaner and system specification.
Fan wear can produce a similar drift. Worn blades, contamination, belt deterioration, slipping drives or changes in rotational speed may reduce performance without stopping the fan completely. The UAE sources supplied do not establish a numerical fan-wear limit. Fan speed, motor speed, electrical power consumption, pressure behaviour and volume flow can instead be examined against the documented original or required performance.
Sharjah OSHJ-GL-12 Section 5.5.3 states that flexible ducting should be kept to a minimum "as it tends to wear more quickly and offers higher resistance to air flow". A worn flexible section may split, collapse, kink or become internally rougher, while an unnecessarily long section may add resistance even before visible damage appears. The Guideline gives no universal maximum flexible-duct length or numerical resistance allowance, so the actual arrangement must be judged against the system design and measured performance.
Multi-branch systems depend on resistance being distributed so that every inlet receives suitable airflow. A damper that moves, is adjusted without documentation or becomes partly obstructed can increase one branch flow while reducing another. A total system reading near the fan may then appear acceptable even though one hood no longer performs as intended.
Sharjah OSHJ-GL-12 Section 5.5.3 states: "Where there are several inlets to an LEV system, balancing will be required to ensure that there is a suitable air flow at each inlet. Without balancing, one inlet may have an excessive air flow at the expense of others which are then not adequate."
No UAE authority located provides a general damper-position tolerance or permitted percentage drift between branches. Suitable airflow must be assessed at each inlet against the system's design specification. A report that records only total volume flow may therefore miss a material imbalance within the distribution network.
Extraction removes air from a room, and replacement air must enter if stable flow is to continue. Where doors are tightly closed, replacement-air openings are blocked or another extract system competes for available air, the room may become negatively pressurised. The fan may continue to run, but the airflow at the hood can fall because the system is attempting to extract from a space that cannot admit enough replacement air.
ADPHC CoP 52.0 Section 3.2(q) states: "Makeup air in the work area shall be sufficient to prevent the creation of negative pressure in the room that will reduce the effectiveness of the LEV." This is a functional requirement. The Code provides no numerical negative-pressure trigger and no universal make-up air quantity for LEV installations.
The fault may be intermittent because room conditions change with doors, mechanical ventilation or other plant. Testing should therefore consider the normal operating configuration rather than only an artificially open room. The absence of a universal numerical trigger means that pressure behaviour and LEV performance must be interpreted together against the installation's intended operating condition.
A hood can lose effectiveness when it is moved away from the source, turned aside, partly covered or separated from the process by a workpiece. ADPHC CoP 52.0 Section 3.5 states: "Hoods shall be located as close as reasonably practicable to the operation." Distance from the source is therefore a design and operating consideration, although the Code provides no universal maximum separation distance.
Workpieces, jigs, storage or temporary screens can also obstruct the intended airflow path. A hood may remain mechanically sound while the process arrangement prevents air from entering as designed. The appropriate assessment is whether the hood remains close to the operation and whether the system achieves its specified performance in the actual working configuration.
ADPHC CoP 52.0 Section 3.2(j) states: "LEVs shall have inspection or clean-out doors not to exceed 4 meters of running length". Four metres of running length is a distance and not a measured quantity, so it carries no averaging period or sampling basis. Section 3.2(k) adds: "A clean-out door shall be provided for servicing the fan and where necessary a drain shall be provided." A blocked, sealed, missing or inaccessible clean-out door can prevent inspection and removal of deposits even where the duct itself remains intact.
ADPHC CoP 52.0 Section 3.1.1(g) states: "Employers shall develop a preventative maintenance plan to ensure LEV works efficiently and according to manufacture specifications." The plan should therefore address the components capable of changing performance, including duct integrity, deposits, filters, dampers, fans, flexible connections, make-up air, hoods, warning devices and access points.
No UAE authority located publishes a numerical trigger for any of the common faults described here. No general permissible leakage rate, maximum filter pressure drop, damper tolerance or fan-wear limit has been identified. The sources are also silent on universal cleaning frequencies and replacement intervals for these components.
Condition and comparison with the system's own specification therefore remain the available tests. A fault is not made acceptable merely because no universal number exists. Where the system no longer matches its design performance, where a stated component duty is breached or where deterioration prevents reliable testing and maintenance, repair or adjustment is required to restore the intended engineering condition.
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 3.1.1(g), 3.2(j), 3.2(l) and 3.2(q); Sharjah OSHJ-GL-12 Sections 5.5.3 and 5.6.1.
Answer: 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 and setting minimum acceptable requirements, says that ducting should be intact without holes or splits. ADPHC Code of Practice CoP 52.0, issued by the Abu Dhabi Public Health Centre under ADOSH-SF and mandatory for employers in the Emirate of Abu Dhabi, states that joints and seams shall be sealed to prevent contaminant loss and contamination of other work areas. No UAE authority located publishes a permissible leakage rate or acceptable hole size for LEV ducting. Integrity and comparison with the system's intended performance remain the relevant tests.
Answer: Sharjah Guideline OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah and setting minimum acceptable requirements, states that systems with several inlets require balancing so that suitable airflow is present at each inlet. It warns that one inlet may otherwise receive excessive airflow at the expense of other inlets that become inadequate. No UAE authority located provides a general damper tolerance or universal allowable percentage difference between branches. Measurements at individual hoods and branch test points must therefore be compared with the system's design specification.
Answer: 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 and mandatory for employers in the Emirate of Abu Dhabi, requires a preventative maintenance plan so that LEV works efficiently and according to manufacturer specifications. Sharjah Guideline OSHJ-GL-12, issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah and setting minimum acceptable requirements, identifies visual condition, effective inward airflow, operational warning devices and intact ducting as relevant checks. No UAE authority located sets universal numerical repair triggers for leakage, filter resistance, damper drift or fan wear. Repair decisions therefore rest on breached component duties, observed condition and failure to meet the system's own specified performance.
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