How to Use Moveable Arm Capture Hoods for Effective Local Exhaust Ventilation
Controlling hazardous substance exposure is critical in any workplace where fumes, dusts, gases, or vapours are generated.
One of the most effective control measures within occupational hygiene is Local Exhaust Ventilation (LEV). Moveable arm capture hoods, including mobile welding fume capture hood systems, provide practical and efficient solutions for many hazardous tasks.
This blog outlines how to use moveable arm capture hoods effectively to ensure workers are protected from hazardous substances, helping with compliance with workplace exposure standards and supporting overall occupational health and safety.
What are Moveable Arm Capture Hoods
Moveable arm capture hoods are part of LEV systems designed to capture contaminants at or near the source before they disperse into the breathing zone and workplace. They typically consist of:
- A flexible articulated arm (often 1.5m – 3m reach)
- A hood or nozzle to capture fumes or dust
- Ducting connected to a fan and filtration/exhaust unit
These systems are commonly used to control welding fume, but are also suitable for soldering, grinding, or any localised task generating hazardous airborne substances
Why Use Moveable Arm Capture Hoods
The hierarchy of controls in occupational hygiene & health and safety management prioritises elimination and substitution first, but when those are not feasible, engineering controls such as LEV become vital. Moveable arm capture hoods:
Allow targeted capture close to the source
Are flexible for multiple work locations
Reduce general area contamination
Protect workers by preventing inhalation of hazardous substances
Steps to Use Moveable Arm Capture Hoods Effectively
1 Conduct Routine Pre-Use Checks
As part of your local exhaust ventilation pre-use checklist, ensure:
- Hoses and ducting are free of holes/cracks or blockages.
- Filters are installed correctly and not clogged.
- The fan and filtration system are operational.
- Extraction airflow is suitable at the hood opening (e.g. airflow indicators).
- The unit is serviced according to manufacturer recommendations and has had at Thorough Examination and Test (TExT) within a 14 month period or sooner if required.
2 Position the Hood Correctly
The efficiency of a moveable arm capture hood is directly linked to its position relative to the fume or dust source. Follow these best practices:
- Place the hood as close as possible (ideally within a half duct diameter distance) to the generation point without obstructing the work.
- Position and angle the hood to ensure the contaminant doesn’t pass into the breathing zone..
- Avoid placing it perpendicular to cross-drafts (e.g. fans or open doors) that can disperse fumes away from the hood capture zone.
3 Adjust and Lock the Arm Securely
Moveable arm capture hoods have articulated joints to enable positioning flexibility. Ensure:
- The joints are adjusted to hold the hood steady in place.
- Any locking mechanisms are engaged to prevent drift during work.
- The arm is maintained regularly to avoid sagging..
4 Switch On Before Work Begin
Always turn on the LEV system before starting the task. Confirm:
- Indicator lights or airflow alarms (if fitted) show normal function.
5 Avoid Obstructing Airflow
Keep tools, materials, or hands from blocking airflow into the hood. Obstructions can:
- Drastically reduce capture velocity.
- Lead to uncontrolled release of hazardous substances into the workspace.
- Cause exposure exceeding occupational exposure limits.
If using the hood for welding, position it to capture fumes rising along the thermal plume, slightly offset from the weld arc to avoid interfering with visibility.
6 Understand Capture Velocity Requirements
Each hazardous substance or task requires a specific capture velocity to effectively control exposure. For example:
- Welding fumes typically require 0.5–1.0 m/s at the hood opening.
- Heavier dusts may require higher velocities to overcome particle inertia.
Capture distance should be stated in your commisionning report or Thorough Examinstion and Test (TExT) report or can also be sated ona lbal on the hood itself. The capture distance specifies the distance at which effective capture of the contaminant will be achieved within, ensuring effective control and compliance.
7 Train Workers in Proper Use
Even the best LEV system fails if users are not trained in:
- Correct positioning techniques
- Recognising when airflow is insufficient
- Reporting damage or performance issues promptly
- Understanding why capture hoods are critical for preventing hazardous substance exposure
Integrate this training within your overall occupational hygiene programme and ensure refresher sessions are conducted annually or when equipment changes.
8 Maintain and Test Systems Regularly
Under COSHH regulation in the UK, LEV systems must be thoroughly examined and tested at least every 14 months by a competent person. For mobile units:
- Record maintenance, filter changes, and any repairs.
- Conduct airflow measurements or checks periodically to verify performance.
- Replace filters as per manufacturer instructions to avoid reduced extraction efficiency.
Common Mistakes When Using Moveable Arm Capture Hoods
🚫 Placing the hood too far from the source, leading to poor capture.
🚫 Using the system with blocked or clogged filters, reducing airflow.
🚫 Failing to adjust the hood to follow the task if workpiece positions change.
🚫 Relying solely on general ventilation or natural dilution without effective LEV capture.
Avoid these by integrating effective supervision and routine inspections within your workplace.
The Role of Occupational Hygiene in Using Capture Hoods
Occupational hygiene professionals assess:
- Task risk levels and required capture velocities
- Equipment suitability for specific contaminants
- System design, commissioning, and performance validation
This ensures moveable arm capture hoods, as part of your local exhaust ventilation strategy, actually control hazardous substance exposure in line with legal and health requirements.
Conclusion: Effective Local Exhaust Ventilation Saves Lives
Moveable arm capture hoods are flexible, powerful tools within your workplace’s LEV systems. When positioned correctly, maintained, and used as part of a comprehensive occupational hygiene program, they significantly reduce exposure to welding fumes, dusts, and other airborne contaminants.
✔ Assess risks
✔ Select suitable hoods
✔ Train staff thoroughly
✔ Inspect, maintain, and test regularly
This approach protects worker health, ensures regulatory compliance, and demonstrates a proactive commitment to workplace safety.
How Can Workplace Exposure Help?
At Workplace Exposure, our LEV testing is carried out by qualified consultants who hold the BOHS Module P601 – Thorough Examination and Testing of Local Exhaust Ventilation (LEV) Systems with a broad range of experience working with all types of systems and workplaces.
Thorough testing is essential for maintaining a safe and healthy working environment, which is why our LEV checks inspect both the visual and working conditions of the system.
The survey ensures that the LEV system is working correctly, efficiently and to the standard required, highlighting any defects and areas for improvement.
Offering all clients a checklist of improvements and maintenance requirements, our team offer professional and thorough checks on all LEV systems. For more information, please get in touch.
Our approach
Get in touch with Workplace Exposure. Either give us a call on 0800 689 4386, or fill in our enquiry form to discuss your monitoring or consultancy requirements.
We’ll then provide you with a no-obligation proposal, we can often give an initial idea of fees whilst we discuss your needs.
Once you’ve accepted our proposal, we can then schedule the work.
Following our site visit we’ll provide you with a comprehensive report giving you advice, recommendations and control measures where appropriate. Implement the outcomes for compliance and a happier healthier workplace.