Boatswain’s Chair vs CDA vs Industrial Rope Access
Boatswain’s Chair, Control Descent Apparatus and Industrial Rope Access are often confused methods of window cleaning and working at height. Although all methods rely on ropes for working at height they are entirely different. This post attempts to describe each method and highlight the differences.
Table of Contents
What Is A Boatswain’s Chair:
According to the International Window Cleaning Association, a boatswain’s chair is a seat for one person, suspended by a single line or tackle, which is designed to be raised and lowered by the user.
The necessary elements for a boatswain’s chair are defined below:
Chair: a soft wooden plank about 24 inches long by 10 inches wide and 2 inches thick. Each corner suspended by 4 rope slings creates a seat for one single worker.
Tackle: pulley blocks and tackle consisting of first grade manila rope five-eighths of an inch. The tackle should consist of rope equivalent in strength to 5,400 pounds. Rope attachment to block shall be by a thimble and splice.
Anchorage: roof anchors, tie-backs, davits, or outriggers suspend the boatswain’s chair in the air.
Fall Arrest System: the trained worker shall wear a safety harness with an attached lanyard secured to a separate independent lifeline.
Training: skilled workers need to be trained on the safe use of both a boatswain’s chair and fall arrest system.
Public Awareness: the area below boatswain’s chair should be barricaded and warning signs should be posted.
The word boatswain has been in the English language since the 15th century. Webster’s dictionary defines it as a naval warrant officer in charge of the hull and related equipment. The phonetic spelling of boatswain is bosun. Shakespeare referred to it as bos’n in his play, The Tempest. Bosun’s Chair was used on ships, the Hoover Dam, and the construction of Mount Rushmore. The incorrect spelling of Bosun’s chair stuck, and is commonly used today.
Although a Bosun’s chair is still used in boating, it’s a very outdated method for working at height. Innovations for working at height have advanced with Control Decent Apparatus and Industrial Rope Access.
Control Descent Apparatus (CDA):
CDA is considered by Cal OSHA a similar method to the Boatswain’s chair. Both are acceptable for window cleaning, if and only if, the windows can’t be cleaned by other means .
Cal OSHA has a higher height threshold for CDA. Boatswain’s chair has a maximum threshold height of 75 feet, whereas CDA has a maximum threshold height of 130 feet. For any projects above these heights, approval must be granted in writing. In addition, the building must have an Operating Procedures Outline Sheet (OPOS) in the case of using either a Boatswain’s chair or Control Decent Apparatus.
CDA is built to only lower the worker down. Boatswain’s chair functions as a pulley with descending and ascending capabilities. The necessary elements for CDA include a working line, controlled descent device; seatboard; personal fall arrest system with a full body harness, lifeline, and locking carabiner (D-ring).
The controlled descent device, seatboard, working lines and safety lines should be used in accordance with manufacturers instructions and permanently marked or tagged with: manufacturer’s name, date made, ID number or length. Unlike a Boatswain chair, CDA is an actual device manufactured by a company.
Shortcomings for CDA & Boatswain’s Chair:
Worker versatility is the obvious drawback for CDA. Control Descent Apparatus isn’t built for ascending or moving laterally. This limits the total reach and overall efficiency for each drop. A worker can only clean, paint, or inspect what is directly beneath them when using Control Descent Apparatus.
Since a Boatswain Chair functions as a pulley the worker has both descending and ascending capabilities but this method is not safe. Workers using a Boatswain’s Chair can not self rescue, therefore prone to suspension trauma.
Suspension trauma is when equipment malfunctions and the worker must rely on their lifeline. The worker doesn’t fall or have a collision accident. The problem occurs when lactic acid circulates the body resulting in cardiac arrest. Suspension trauma occurs from the following chain of events.
When the worker is hanging his leg muscles relax given that there is no opportunity to stand. Compression of the femoral veins by harness groin straps further restrict blood circulation and lactic acid builds up in the legs. Venous pooling in the lower extremities prevents blood from moving up the body to the heart and lungs for recirculation. This causes the heart to work much harder in order to keep vital organs fully supplied with blood.
When the worker is lowered to the ground, stagnate blood and lactic acid buildup in the legs circulates the entire body. High levels of lactic acid flooding the body can overwhelm the kidney, liver, and heart resulting in heart failure. To prevent this chain of events from happening, a worker has a 30 minute window to be rescued and lowered to the ground. Suspension trauma also called harness hang syndrome is a subtle but lethal hazard.
Industrial Rope Access:
Industrial rope access offers a far more comprehensive self rescue and safety plan than CDA or Boatswain chair. For starters, workers are not permitted to work alone. Industrial rope access crews work in teams of two or more with multiple levels of accreditation. Depending on the job, a level 1 has to work with a level 2 or 3. Similar to an airline pilot, each certification level requires the individual to pass in person tests that are sanctioned by international organizations, and log the required amount of hours on rope. SPRAT & IRATA are the major industrial rope access governing bodies.
The risk for suspension trauma is virtually eliminated as industrial rope access equipment allows for self rescue. Industrial rope access technicians wear a full body harness with sub pelvic leg straps and suspension trauma straps for support. This allows workers to contract the leg muscles and stand up in their harness taking pressure off the arteries to restore blood circulation.
The harness directly connects to a descender and backup device that automatically stops when released. This reduces the vertical distance a worker can fall, giving more control during the descent. Each descender and ascender device needs to be compliant with the American National Standards Institute (ANSI).
Industrial rope access enables workers to have controlled ascent, descent, and horizontal climbs. It’s the most versatile work positioning system. Equipment used includes ascenders with foot loops, descenders, carabiners, and cowtails to name a few. Another safety requirement is using a certified helmet with chin strap and side impact padding. This protects the worker from loose debris above by minimizing collisions.
Another major difference between industrial rope access and CDA or Boatswain’s chair is with regards to rigging. Rope Access requires two independent anchor points and two lines. Comprehensive rigging plans and load testing follows strict protocols and guidelines.
Why Hire RayAccess:
RayAccess employs certified industrial rope access technicians. In addition to rope access, our technicians are cross trained in window cleaning, pressure washing, and waterproofing services. They are also equipped to use the full spectrum of access methods including boom lifts and suspended scaffolding. We carry comprehensive insurance and have been servicing Los Angeles and surrounding areas since 2011.
- State of California, Department of Industrial Relations. Manual Boatswain’s Chairs and Controlled Descent Apparatus (CDA). https://www.dir.ca.gov/title8/3286.html
- Occupational Health & Safety. Suspension Trauma. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2658225/
- National Library of Medicine. Suspension Trauma. https://ohsonline.com/Articles/2017/01/01/Suspension-Trauma.aspx?Page=1
- State of California, Department of Industrial Relations. Use of Rope Access Equipment. https://www.dir.ca.gov/title8/3270_1.html