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Calculating Compound M/A

Tuesday, June 13, 2017

We recently had a request for additional information beyond what was shown in our “Theory of Mechanical Advantage” video by Chief Instructor Dennis O'Connell. The reader would like to know more about calculating compound mechanical advantages.

First of all, a simple mechanical advantage (MA) is quite easy to calculate as long as you follow a couple of basic rules.

MAs are generally expressed in numeric ratios such as 2:1, 3:1, 4:1, etc. The second digit of the ratio, or the constant "1" represents the load weight. The first digit, or the variable 2, 3, 4, etc. represents the theoretical factor that we divide the load weight by, or inversely multiply the force we apply to the haul line.

I say theoretical as these calculations do not take into account frictional losses at the pulleys and resistance to bend as the rope wraps around the pulley tread. So a 3:1 mechanical advantage would make the weight of a 100-pound load feel like 33 pounds at the haul line, but we do lose some advantage due to those frictional losses. An even more important consideration is the fact that we multiply our hauling effort by the variable, which is important to understand when we think about the victim or an on-line rescuer that has become fouled in the structure. This is also important when considering the stresses on the haul system including the anchor, rope, and all components in the system.

We also need to pay attention to the amount of rope that must be hauled through the system to move the load a given distance. If we are using a 4:1 MA and need to move the load 25 feet, we need to pull 100 feet of rope through the system (4 X 25 feet = 100 feet).

To calculate a simple MA, remember this: if the anchor knot is at the load, it will be an odd mechanical advantage (3:1, 5:1, 7:1, etc.). If the anchor knot is at the anchor, it will be even (2:1, 4:1, 6:1, etc.) “even/anchor-odd/load.” And if you count the number of lines coming directly from the load, you will determine the variable (remember not to count the haul line if it passes one final change of direction pulley). For instance, if the knot is at the anchor and there are four lines coming from the load, this will result in a 4:1 simple MA. And if your haul line is being pulled away from the anchor, that only means you have created one final change of direction which oftentimes is done to allow the addition of a progress capture device (ratchet), or simply to make it a more convenient direction of pull. But this 5th line, called the haul line, does not come directly from the load. It comes from the final directional pulley to the haul team and is not to be counted in the simple MA ratio. We would call this set up a 4:1 MA with a change of direction (CD).

Calculating compound MAs is also quite easy. Compound MAs (sometimes called a stacked MA) simply means we are attaching a second MA to the haul line of the original MA. When we do so, we multiply the first digit of the original MA by the first digit of the second MA. If you attach a 2:1 MA to the haul line of a 4:1 MA (2 X 4 = 8), you end up with an 8:1 compound MA. Keep in mind that we have added even more frictional losses into this system, but it is still a pretty powerful MA.

There are potential benefits as well as potential penalties when using compound MAs. One benefit includes using less gear when stacking MAs. For instance, to build a simple 6:1 MA, you will require at least five pulleys, and if you want a final CD, that would require one last pulley for a total of six pulleys. If you decide to build a 6:1 compound MA, you can get away with as few as three pulleys by attaching a 2:1 MA to the haul line of a 3:1 MA. If you wanted one final CD, you would again add one more pulley for a total of four pulleys. The obvious advantage is that fewer pulleys are required, but hidden in there as another advantage is fewer pulleys for the rope to wrap which translates to less frictional loss and bend resistance.

Another benefit to stacking MAs may be the reach you need to attach to the load. If the load is 25 feet away from the anchor and you are using a 6:1 simple MA, you will need at least 150 feet of rope, plus some extra to tie the anchor knot, and some spare to wrap over the final directional - if you use one. If the load is 50 feet below the anchor and you want to stick with the simple 6:1 MA, you are looking at a minimum of 300 feet of rope.

So, what if we send a 3:1 MA down from the anchor to the load 25 feet below and attach a 2:1 to the haul line of the original 3:1 to build a 6:1 compound MA?

Well, in this case we would need 75 feet of rope plus some extra for knots for the original 3:1, and two times the length of the compounding MA throw. Throw? What the heck is throw? Throw is a term we use when we have a limited distance between the compounding MA anchor and where we can safely attach the compounding MA to the haul line of the original MA.

In the diagram below you can see the original 3:1 MA extending from its anchor to the load. The added MA, which in this case is a 2:1 has a total throw of 10 feet which requires a little over 20 feet of rope to construct. So, if we add the 75+ feet of rope required for the original 3:1 to the 20+ feet for the added 2:1, we arrive at a bit over 95 feet of rope required for this compound 6:1 MA to reach a load 25 feet from the anchor. This can be two separate ropes, one a bit over 75 feet and a second a bit over 20 feet, or it can be one rope a bit over 95 feet that we can treat as if they were two separate ropes. More on that in a bit.



Remember that we must consider the amount of rope that we need to pull through the system in order to move our load the required distance. So, using a 6:1 compound MA to move the load 25 feet we must pull a total of 150 feet of rope through the system. Whoa, wait a minute! I thought we determined that our total rope needs were only a bit over 95 feet, so how did we come up with 150 feet of rope? One of the disadvantages of compound MAs is the need for resets when the throw is not long enough to move the load the needed distance. So, even though we are using in the neighborhood of 95 feet of total rope, we are pulling the same section of rope through the second MA multiple times.

Well, this is one of the big disadvantages of a compound MA. We need to reset the system multiple times to move the load the required distance. To help envision a reset cycle, let’s assume we have our original 3:1 mounted to an anchor, and 25 feet from that anchor is the 3:1 attached to the load. The haul line of the original 3:1 goes through a final CD, and we have attached a ratchet at that final CD to capture the progress of the loads movement. One option is to find a second anchor and in this case we found one 10 feet away from the final CD of the 3:1. We tie an anchor knot and attach it to that second anchor and route the remaining 20+ feet of rope through a pulley which we attach to the haul line of the original 3:1 with a rope grab. We now have our 2:1 pulling on the haul line of a 3:1 resulting in a 6:1 compound MA.  But…… and there’s always a “but,” isn’t there? We can only move the load a bit over 3 feet at a time before we completely collapse the 2:1 and need to reset it for the next haul. Remember, the 2:1 only has a 10-foot travel or “throw” and that distance is divided by 3 as it is pulling on a 3:1 MA. In addition to that, we have pulled about 20 feet of rope through the 2:1 just to move the load a bit over 3 feet. In order to move the load the entire 25 feet we will need to reset the system about 8 times and that is some slow going. Just to point out one option to speed up the haul by reducing the amount of resets needed, if you sent the original MA to the victim as a 2:1 and then stacked a 3:1 MA with 10 feet of throw onto that 2:1, you would still have your compound 6:1 but would only need to do about 5 resets and could do it with a bit over 80 feet of rope.




There are all sorts of options when deciding what type and ratio of MA to use in a rescue effort. You can get pretty creative when building MAs, but be aware that creativity can sometimes lead to crazy. Remember the KISS principle…keep it simple and safe.

If you are overbuilding an MA just to show a cooler way of doing it, you may be missing the point of the job. There is someone in trouble that is relying on you getting them up and out of their predicament, and sometimes we can get a little carried away with our creativity, especially when it comes to MAs. 3:1 Z-rigs are a great option especially with the addition of devices like the Petzl ID or the CMC MPD as your first MA change of direction and progress capture device. Plus, this gives you the ability to convert to a lower with friction control already built in. But you can really complicate things by compounding a second MA onto a Z-rig to get a higher ratio MA. You will soon learn that now you have to perform two separate resets of the haul cams. And, if you are out of sequence in the reset, the haul cam of the second MA will jam into the traveling pulley of that system and stop you in your tracks. There are some tricks to really make the resets for this system go nicely, but that will have to wait for another day.

There are hundreds of variations that you can use for compounding MAs, but once again I caution you to remember KISS. I have my favorites and every once in a while the situation calls for something a little different, and that’s where understanding the advantages and disadvantages of the systems is of great value.

For additional video resources on mechanical advantage as well as other techniques and systems, visit Roco Resources.

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Cal/OSHA Cites Two Companies After CS Death

Tuesday, May 30, 2017

On Oct. 21, 2016, a D&D Construction employee entered a drainage shaft to clean out mud and debris. No personal fall protection was utilized as the worker descended via bucket 10 ft. into the shaft, which was 4.5 ft. in diameter and lined with concrete.

At some point, the worker lost consciousness due to the oxygen deficient atmosphere in the confined space and fell 40 ft., then drowned in a foot of water.

“Cal/OSHA launched a confined space educational program to bring attention to the dangers and preventable deaths that occur in confined spaces,” said Cal/OSHA Chief Juliann Sum in a statement. “The program helps employers identify hazards and create effective safety plans that include air monitoring, rescue procedures and training before work begins.”

General contractor Tyler Development was constructing a single-family residence in the Bel Air area and hired subcontracted D&D Construction to install and service reinforced concrete posts known as caissons on the property, according to the agency’s report.

The state-run occupational safety unit cited Tyler Development and D&D Construction Specialties Inc. a combined $352,570 for ten serious and willful health and safety violations following an investigation. Cal/OSHA said neither company was in compliance with required confined space procedures.

D&D Construction previously was cited in 2012 for similar safety violations at a different job site.

In total, D&D has to pay a proposed $337,700 for 13 violations, including two willful serious accident-related, one willful serious, one serious accident-related, six serious, and three general in nature.

According to Cal/OSHA, the company failed to:
• ensure safe entry into the confined space
• have an effective method to rescue the worker in the confined space in an emergency
• test the environment to determine if additional protective equipment, such as a respirator or oxygen tank, were required to work safely in the shaft.

Tyler Development was cited $14,870 for five violations, three of them serious, for a failure to:
• evaluate the worksite for possible permit-required confined spaces
• ensure that the subcontractor meets all requirements to comply with a permit space program
• protect workers from the hazard of impalement by guarding all exposed reinforced steel ends that extend up to six feet above the work surface with protective covers

A full copy of the report is available here.

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Roco CASEVAC II for Tactical Team Members

Wednesday, May 10, 2017

Crank It Up a Notch with Roco’s CASEVAC II Training

It has been an honor for us to expand our support of our nation’s heroes to the greater SOCOM community. When we developed the TCCC CASEVAC Extraction kits and subsequent training, our goal was to assist operators around the world in saving the lives of their buddies in need. While SOCOM did a commendable job in bridging a broad capabilities gap with the CASEVAC Set, a training gap still exists for more advanced extraction training.

Roco trained over 700 operators within all four branches of our military during the time we offered NET courses at the Roco Training Center. Now that this training and equipment has been used in the field for a few years, we would like to propose the following questions:

  • When was the last time you practiced the skills learned in the NET course?

    Or, broke out the Micro RIES® and built a haul system?

    Or, the last time you lifted a vehicle or debris using the lift bags?

    What about the skills that the NET course didn’t cover?

Now is the time to take it to the next level with Roco’s CASEVAC Extraction Level II. This course builds upon the foundation of the skills offered in the NET course and gives operators a few more ways to get the job done.
The beauty of these “rescue” skills is that most of them can be applied to everyday missions outside of the context of rescue. If you can haul Mongo onto a roof while he’s packaged in a Sked litter, then you can definitely haul up some equipment. If you can rappel into a well to save a fallen teammate and ascend back out, then you can access and bail out of OPs more quickly, safely, and efficiently. Lifting and extrication tools and techniques can be applied to SSE as well as rescue.

We’d like to invite you to help drive the curriculum of this course. Roco will be holding two (2) pilot courses in order to validate the curriculum we’ve developed. A detailed description is located at our Tactical Courses page. Your feedback will help determine which skills are vital to include.
Not currently under SOCOM’s umbrella? No worries. While this course was designed with the CASEVAC Set of equipment in mind, the principles apply universally.
Since equipment changes, we focus on the principles. In this course, we start from the ground up, refreshing things covered in NET, and using equipment from the CASEVAC Set as well as gear that is used by other SOF units around the world. By using several variations of equipment, you’ll gain higher proficiency and be able to use your team’s equipment more effectively, whether it’s the CASEVAC Set or not.
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The Clock's Ticking on Timely Response

Tuesday, April 25, 2017

By Dennis O'Connell, Roco Director of Training & Chief Instructor

As Director of Training, I get many questions about rescue techniques and regulations from our students and readers. In the past month alone, I have received three inquiries about "timely response for rescue teams" regarding permit required confined spaces (PRCS). So, let's break it down and try to clear the air on this subject. For clarification, we will refer to the General Industry Standard 1910.146; the Construction Standard 1926-1211; and the Respiratory Standard 1910.134.

In 1910.146, OSHA provides guidance on timely response in Subpart K (Rescue and Emergency Services) and again in Non-Mandatory Appendix F (Rescue Team or Rescue Services Evaluation Criteria). Subpart (k)(1)(i) states: "Evaluate a prospective rescuer's ability to respond to a rescue summons in a timely manner, considering the hazard(s) identified."

This one sentence actually says volumes about response times. The first question to be answered is, "Can the rescue service respond in a timely manner?" It then gives a hint as to what a timely manner should be based on. The second part of the sentence refers to "considering the hazard(s) identified." What this so eloquently says is the response time must be determined based on the possible hazard(s). This means the "known and potential hazard(s)" must be identified for each space to be entered. The hazards discovered -- based on severity, type, how rapidly the hazard could become IDLH or injure the worker, how quickly the need to treat the injury, or how quickly hazards might interfere with the ability to escape the space unaided -- would then be used to determine an acceptable response time. This is why OSHA only alludes to response times and does not set hard and fast times to follow -- it depends on the hazards of that particular space.

Another aspect we need to consider is that "response time" begins when the call for help goes out, not once the team is on scene. It ends when the team is set-up and ready to perform the rescue. So, how long will it take your team to be notified, respond and set-up is a big portion of that acceptable response time calculation. For example, a dedicated onsite fire/rescue team would be able to respond faster than workers who have other responsibilities and need to meet at the firehouse before responding. Or, more quickly than an outside service, such as a municipal department, that would have to respond to the facility, get through the gate, and be led to the scene.

In the note to paragraph (k)(1)(i), it adds: What will be considered timely will vary according to the specific hazards involved in each entry. For example, OSHA 1910.134, Respiratory Protection, requires that employers provide a standby person or persons capable of immediate action to rescue employee(s) wearing respiratory protection while in work areas defined as IDLH atmospheres.

Here we see OSHA better defining an acceptable response time for IDLH atmospheres -- i.e., immediate action! However, it's important to note this doesn't just refer to low O2...depending on the type of contaminant in the atmosphere, other respiratory equipment such as half- or full-face APRs could be used. It may include a dusty environment where the entrant wears a mask and visibility is less than 5 feet. Technically, that would be considered an IDLH environment. Many people get hung up on the use of SAR/SCBA as the trigger for a standby team, and that is just not the case.

For an IDLH atmosphere where respiratory protection is needed, an adequate number of persons (rescuers) is required to perform a rescue from the type of space involved - ready, trained, equipped and standing by at the space -- ready to take immediate action should an emergency occur. So, when dealing with possible IDLH atmospheres, we are looking at "hands-on" the patient in 3-4 minutes as possibly being an appropriate response time. Basically, this is about how long an entrant can survive without air. The only way to safely make rescue entry in that time frame is to have rescuers standing by, suited up and ready to go!

So, if dealing with an IDLH atmosphere, we revert back to 1910.134. Many people think that that is the only time we need a team standing by ready to take immediate action. I pose the question, "If the hazard is a liquid (engulfment hazard), what would be a reasonable response time?" If the victim is Tarzan or Johnny Weissmuller (okay, Michael Phelps, for you younger people), we may have a longer stay-afloat time. But if a non-swimmer, or in an aerated solution or other engulfment hazard, immediate action may be their only chance of survival! And, what about radiation (time, distance, shielding)? I am sure you can think of a few more possibilities.

And, while OSHA referred to an IDLH atmosphere in this example, it's important to consider other IDLH hazards as well. Here's where we note that the definition of IDLH in the Respiratory Standard (1910.134) differs slightly in Permit-Required Confined Spaces (1910.146). The Respiratory standard specifically refers to an IDLH "atmosphere" while the PRCS standard states the following: Immediately dangerous to life or health (IDLH) means any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that would interfere with an individual's ability to escape unaided from a permit space. This includes more than simply atmospheric hazards! 

OSHA NOTE: Some materials -- hydrogen fluoride gas and cadmium vapor, for example -- may produce immediate transient effects that, even if severe, may pass without medical attention, but are followed by sudden, possibly fatal collapse 12-72 hours after exposure. The victim feels "normal" until collapse. Such materials in hazardous quantities are considered to be "immediately" dangerous to life or health.

In Non-Mandatory Appendix F (I hate that non-mandatory language), OSHA gives guidance on evaluating response times under Section A - Initial Evaluation. What are the needs of the employer with regard to response time (time for the rescue service to receive notification, arrive at the scene, and set up and be ready for entry)? For example, if entry is to be made into an IDLH atmosphere, or into a space that can quickly develop into an IDLH atmosphere (if ventilation fails or for other reasons), the rescue team or service would need to be standing by at the permit space. On the other hand, if the danger to entrants is restricted to mechanical hazards that would cause injuries (e.g., broken bones, abrasions) a response time of 10 or 15 minutes might be adequate.

Not a bad paragraph for a non-mandatory section of the standard! Here they explain what they are looking for in regards to response times. They even take the OSHA 1910.134 IDLH atmosphere requirement for a team standing by at the space a little further by adding "or into a space that can quickly develop into an IDLH atmosphere." It also states if the hazard is mechanical in nature, 10-15 minutes might be adequate. That’s right, "might" not will be, but might be. Again, it depends on the hazard.

Paragraphs 2-7 in Appendix F goes on to describe other conditions that should be considered when determining response times such as traffic, team location, onsite vs. offsite teams, communications, etc. If you have not done so, I highly recommend that you review the not-so-Non-Mandatory Appendix F. It is also important to note that while it's not mandatory to follow the exact methods described in Appendix F, meeting the requirements are! OSHA also uses the word "should" in Appendix F, not following the OSHA recommendations could certainly lead to some hard questions post incident.

OSHA 1926 Subpart AA Confined Spaces in Construction closely mirrors 1910.146. In this relatively new standard, they simplified the definition of timely response and omitted Non-Mandatory Appendix F, which helps to eliminate the confusion of the "non-mandatory" language, and included the requirements right in the standard, which is good. However, 1910.146 really gives you a better idea of what timely would be for different situations through the notes in Section (k) and Appendix F.

Section 1926.1211 of the Construction Standard for Rescue and Emergency Services (a)(1) states: Evaluate a prospective rescuer’s ability to respond to a rescue summons in a timely manner, considering the hazard(s) identified. This is immediately followed by: Note to paragraph 1926.1211(a)(1). What will be considered timely will vary according to the specific hazards involved in each entry. For example, OSHA1926.103, Respiratory Protection (for construction) requires that employers provide a standby person or persons capable of immediate action to rescue employee(s) wearing respiratory protection while in work areas defined as IDLH atmospheres.

In closing, these regulations are driving you in the same direction for identifying what a timely response would be...THERE IS NO SET TIME FRAME! Each space must be evaluated based on potential hazards and how quickly rescue would need to take place. I hope this will make you take a closer look at "how and what" you consider a timely response. An employer's PRCS program must identify and evaluate the rescue resources to be used. It is then up to the entry supervisor to make sure the identified rescue service is available to respond in a timely manner, which can literally mean life or death for the entrants.

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VPPPA Region VI in Little Rock, AR

Tuesday, April 25, 2017

FreeTech™ Harness Demo

Visit with Josh, Pat and Aimee
Dates: May 1-3
Location: Little Rock Marriott
Little Rock, AR
Booth: #911


To read more information or watch the video of this new figure-8 style fall protection harness and its unique SwitchPoint™ System technology that may help prevent the onset of suspension trauma, click the picture on the left. Or, you can also click here.

We look forward to seeing you there!

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