Capture hoods are the point at which a local exhaust ventilation system meets the process. Their design and position determine whether released dust, fume, vapour, gas or mist enters the air stream or escapes into the surrounding workplace. UAE source material does not provide one general capture velocity for all hoods. Instead, the published Abu Dhabi and Sharjah documents emphasise enclosure, proximity, effective capture and process-specific design, while leaving universal numeric velocity values unstated.
Sharjah OSHJ-GL-12 Local Exhaust Ventilation, issued by the Sharjah Prevention and Safety Authority under the Occupational Safety and Health System in Sharjah, identifies enclosing, receiving and capturing as the basic hood types in Section 5.5.2, "sometimes referred to as receptor and captor". 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.
An enclosing hood contains the source as fully as the process permits. A receiving hood is positioned to receive a contaminant-laden air stream that already has direction or momentum. A capturing hood must draw the contaminant towards the inlet against competing air movement. These categories describe the relationship between hood and source rather than the shape of a particular product. The category name does not by itself establish a testing method, an inspection interval or a numeric acceptance value; those matters must come from an applicable process provision or specification.
The Sharjah Guideline states, with its own grammatical error: "An enclosing hood are more effective than capturing or receiving hoods" (sic). The central engineering point is that enclosure reduces the amount of uncontrolled space across which contaminants must be captured. The statement does not publish an effectiveness percentage, airflow value or velocity criterion, and no such figure should be inferred.
Sharjah OSHJ-GL-12 distinguishes full enclosure, room enclosure and partial enclosure. Full enclosure places the process within a contained arrangement, apart from openings needed for access, material movement or operation. Room enclosure uses a room or defined space as the enclosing boundary. Partial enclosure surrounds only part of the source and depends more heavily on airflow through the remaining opening.
The difference affects susceptibility to cross-draughts, process movement and operator interference. A more open hood generally relies on capture across a larger uncontained region, whereas enclosure channels replacement air through controlled openings. The Sharjah source does not attach one general airflow value or opening velocity to these categories, so the distinction remains qualitative unless a process-specific provision applies. The classification helps describe how much of the source is physically contained, but it does not turn every enclosure into plant with identical airflow needs.
ADPHC CoP 52.0, issued by the Abu Dhabi Public Health Centre under ADOSH-SF, contains provisions for enclosure-type LEV and specific processes. ADPHC Codes of Practice are mandatory for employers in the Emirate of Abu Dhabi. The Code does not convert the categories into one universal hood performance number, and its process-specific figures should not be applied to unrelated plant.
The examples in Sharjah OSHJ-GL-12 include flexible hoses and captor hoods, lip extraction, and "Soldering extractors, including 'tool-tip' extraction systems". Flexible hose arrangements allow an inlet to be positioned near a changing task. Lip extraction draws air along the edge of a source or opening. Tool-tip extraction places the inlet directly beside a small point of generation.
The soldering reference is the only located mention of soldering extraction in any UAE instrument within the supplied material. It appears as an example of a hood type and carries no testing duty and no interval. It should not be presented as a separate certification rule, nor does it establish a general velocity for soldering extraction.
These examples reinforce the importance of geometry and proximity. A small inlet near the release can act differently from a larger hood located farther away, even when both connect to the same air mover. Selection therefore depends on how the contaminant is generated, its direction of travel, the process layout and the extent to which the source can be enclosed.
Sharjah OSHJ-GL-12 Section 5.5.1 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 duct diameter is a distance and one tenth is a ratio. Neither is a published velocity value, and neither requires an averaging period or sampling basis.
The statement illustrates rapid loss of influence with distance. Air speed at the hood face should not be assumed to persist unchanged into the surrounding space. Moving a hood away from the source, even while leaving the fan operating, can substantially weaken capture where the contaminant is released.
The ratio is not a substitute for a design calculation or process-specific criterion. It does not identify the face velocity, duct diameter, hood geometry, contaminant momentum or surrounding air movement for every installation. Its purpose is to explain why incorrect positioning can defeat a hood that appears operational. Visual evidence that an inlet, flexible hose or fan is present does not answer whether the contaminant release lies within the hood's effective influence. Position is therefore part of functional design rather than a secondary housekeeping matter.
Sharjah OSHJ-GL-12 Section 5.5.1 states: "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". The Guideline names capture velocity as a design concept and defines its unit, but it publishes no general number for it.
That silence is important. No UAE authority located publishes a general capture velocity value for any hood. The only numeric velocities supplied by ADPHC CoP 52.0 are process-specific values for spray booths, fume and laboratory hoods, and grinding, polishing and buffing enclosures. Those values belong to their stated applications and cannot be repurposed as universal hood criteria.
A hood can consequently be discussed in terms of enclosure, location, process relationship and effective capture without inventing a velocity. Where a manufacturer specifies a performance condition, the plant can be assessed against that specification. Where a process-specific authority provision applies, that provision can be used within its scope. The supplied sources do not authorise a generic value for all other hoods. Where no process-specific value is published, the absence should remain visible in the specification and assessment rather than being concealed by a figure borrowed from an unrelated hood type.
ADPHC CoP 52.0 Section 3.5 requires manufacturer-supplied hoods on all grinding and abrasive cutting-off wheels. It states: "Equipment shall not be used unless a hood is in place". It also states: "Hoods shall be located as close as reasonably practicable to the operation". These are direct requirements for employers in the Emirate of Abu Dhabi under a mandatory ADPHC Code of Practice.
The Code further requires the adjustable tongue to be "kept in working order and shall be adjusted within one-quarter inch of the wheel periphery at all times". One-quarter inch is a distance, not a measured quantity, so it has no averaging period or sampling basis. The provision connects hood integrity and close adjustment with safe operation of the specified equipment.
Section 3.5.2(a) records that a temporary enclosure "greater than 2.5m x 2.5m x 3.0m shall be considered large". These are dimensions defining an enclosure category, not measured exposure or airflow quantities, and no averaging period or sampling basis applies. The classification should remain within its Abu Dhabi context rather than becoming a general definition for every authority.
Related matters remain on four 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 page is confined to hood engineering and does not address personal exposure monitoring, health effects, airborne contaminant sampling or kitchen extract cleaning.
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.
Sharjah OSHJ-GL-12 Sections 5.5.1 and 5.5.2; ADPHC CoP 52.0 Version 4.1 Sections 3.5, 3.5.1 and 3.5.2(a).
Sharjah OSHJ-GL-12, a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements in the Emirate of Sharjah, identifies enclosing, receiving and capturing hoods, with receiving and capturing also described as receptor and captor types. Enclosing hoods contain the source, receiving hoods accept a contaminant stream with existing direction, and capturing hoods draw contaminants towards the inlet. The Sharjah Guideline states that enclosing hoods are more effective than capturing or receiving hoods, but it publishes no universal effectiveness percentage or velocity value.
No UAE authority located in the supplied material publishes a general capture velocity value for every hood. Sharjah OSHJ-GL-12 is a Sharjah Prevention and Safety Authority Guideline setting minimum acceptable requirements and says that different situations require different velocities and solutions, but gives no general number. ADPHC CoP 52.0 is mandatory for employers in the Emirate of Abu Dhabi and contains only process-specific numeric velocities for spray booths, fume and laboratory hoods, and grinding, polishing and buffing enclosures. Those process-specific values cannot be treated as universal criteria.
ADPHC CoP 52.0, issued by the Abu Dhabi Public Health Centre under ADOSH-SF, is mandatory for employers in the Emirate of Abu Dhabi and requires manufacturer-supplied hoods on all grinding and abrasive cutting-off wheels. The equipment must not be used unless a hood is in place, and the hood must be located as close as reasonably practicable to the operation. The adjustable tongue must be kept in working order and adjusted within one-quarter inch of the wheel periphery at all times; that figure is a distance and not a measured quantity, so no averaging period or sampling basis applies.
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