4.3 Helmet Integration (REDLINE)
Building upon the earlier work for what became the RD1 components and systems available to consumers, I began to explore integrated life systems, which I define as marriages of various diving modalities. Here, I describe the interface of a rebreather with a conventional surface supplied air diving helmet.
I branded the project REDLINE (Range Extension for Depth and Linear Exploration) given its intended purpose as a platform for more ambitious range extensions in the future. The design process followed through by meeting the principles described in this content.
System Description
Broadly, the REDLINE helmet integration is a closed-circuit rebreather that is back-mounted, has variable volume vital capacity, and a single axial scrubber. The system incorporates onboard oxygen and diluent cylinders with gas plumbing that also allows the diver to incorporate a secondary onboard or offboard oxygen and diluent gas supply for redundancy. The unit is manually controlled with user-variable oxygen flow injection via a needle valve, and its oxygen partial pressure is gauged using three oxygen sensors. Redundant oxygen partial pressure displays are used in varying configurations depending upon mission requirements. The system incorporates a flood-tolerant exhalation cavity design with a mechanism to evacuate water from the breathing loop. In its entirety, this is a conventional mCCR, though adding the helmet integration introduces some complexity and careful consideration must be placed on bailout strategies given the helmet interface. This basic envelope is what I've now advocated as the mCCR build for RD1 (less the helmet of course).
The system may be dived fully autonomously or semi-autonomously with surface supplied diluent gas delivery utilized as the primary or backup gas supply depending on project requirements. This variety of configurations provides a suitable platform for diverse applications within exploration, scientific, commercial interventions.
| Helmet integrations can be dived autonomously, or semi-autonomously (telemetry only), to reduce or eliminate the umbilical under special circumstances. |
Technical Overview & Principles of Design
When the rebreather's utility function is outside the scope of what is more commonly embraced as self-contained rebreather diving, we arrive at a very interesting point in the innovation process where standards need to be written, evaluated, and adopted. Of course, this should be accomplished with some response to demonstrated needs and maintaining familiar technical conventions such that adoption is as seamless as possible.
What happens when a rebreather is needed for ‘work’, particularly in an industrial setting?
| Among the very few applications of helmet integrated rebreathers was a technical demonstration by the JF White Contracting Company's Diving Division to mock-up a distance tunnel penetration. This image was among those truly inspiring to me personally! |
Helmet Integration & Functions
Helmet integrations are not a new concept per se, as bailout rebreathers are used from deep saturation or bell excursions from time to time. In this application, failure of the primary breathing gas supply would prompt the diver to actuate the rebreather device, affording a rather short period (perhaps tens of minutes) to return to the bell or habitat. This application is a semi-closed rebreather, though is still significantly longer than if using open-circuit bailout techniques (only a handful of minutes, or even handful of individual breaths pending the depth). Given scrubber TBL limitations with depth described previously, relying on closed circuit breathing apparatus for primary life support at extreme depth and for lengthy durations is not practical and poses limitations. A diver hard at work might easily over-breathe the scrubber causing severe consequences from elevated carbon dioxide partial pressures coupled with high resistance from the gas density through the circuit which escalates the physiological CO2 retention issues.
This vision for working rebreather divers in the deep is therefore somewhat misguided. That is not the sweet spot for the technology. Short bounce dives to extreme depth are feasible and are conducted in the scientific and private exploration sectors, though consider that the bulk of these dives are spent in the shallows decompressing. The full life support capacity is not exhausted at a static depth. There are aspirations to embrace CCR at depth given capabilities afforded by stationary habitats, though this carries substantial risk - issues pertaining to bulk-loading the scrubber must become better understood and mitigated.
Where is the utility value of rebreathers in a working environment? Well, right where their sweet spot has been established for decades, say 60fsw to 300 or perhaps 400fsw where the diver benefits from lengthy surface-to-surface excursions made possible with optimal pO2’s, warm/moist breathing gas, and multiple redundancies built in for bailout considerations, or in very shallow water where long distance infrastructure penetrations are required. These types of interventions are increasingly serviced robotically, leaving only a narrow and highly specific niche for the capability.
To transition from more autonomous self-contained rebreather diving to working rebreather diving, several fail-safes from the commercial diving convention should be considered for adoption. This all starts with protecting the head.
A working diver’s helmet is essential personal protective equipment (PPE). When at work, we are often inside or beneath structure, may have objects swinging overhead, and can’t risk losing a mouthpiece or having life support torn from our mouths. Further, the water may be contaminated. Additionally, it is logical and highly advantageous to provide the highest clarity two-way voice communications available to afford a diver-to/from-surface telemetry for effective team management. All of these needs are best met with a diver’s helmet.
| Helmet equipped with rebreather interface, lights, and a camera. The bailout valve (BOV) is a rigid mount to the helmet, shifting the stock regulator to a low position. Closing the white lever switches from closed circuit to open circuit (for bailout purposes). |
Secondly, being tethered to the surface provides for a direct path to return to the point of entry, even in poor visibility conditions or when it is necessary to navigate within and through submerged structure. This tether may provide a variety of essential safety functions such as two-way voice communications, video and power capabilities, data transmission, a redundant gas supply, hot water to the diver, and a strength member for emergency extrication of a diver needing to be recovered.
So, the average commercial diver will argue that both the helmet and tether or umbilical are far preferred over autonomous (scuba) techniques in most instances. Indeed, there are tremendous benefits. To the contrary, the average scientific diver will tell you that this equipment is burdensome, inhibits freedom to move about unencumbered, and is cost prohibitive. Both camps come from a degree of bias to their respective community standards of practice and generally lack experience in the opposing sector.
Moving things forward, I believe there is a cross-section of working diver space that would benefit measurably from using rebreathers on a more routine basis. The benefits of the technology are clear, though the challenge remains in equipment configurations that provide for a very simple and intuitive marriage of these two distinct platforms: surface supplied diving and closed-circuit rebreathers. Thereafter, of course, operational standards, training, and proficiency activity needs to be worked in to the established regimen; all of which represent an investment that few are likely to make until a market opportunity is well demonstrated.
Logic for Systems Integration
Several careful considerations must be made when integrating a diver’s helmet with a rebreather. For consideration throughout this section, we will assume integration of a Kirby Morgan brand Superlite helmet. The Superlite 17k is particularly well suited for this integration, though is not the only helmet suitable.
| The 17k low positioned water dump can be fit with a positive pressure toggle dump valve for controlled water egress without losing gas. Other water evacuation hardware can be incorporated into other helmet designs when the low positioned vent is not available. |
Note: While we describe use of Kirby Morgan brand products, Kirby Morgan has in no way endorsed nor approved modification of their equipment for this project.
Integration logic and principles include the following:
● The integration design must provide for minimal dead space between the diver’s mouth/nose and the breathing loop to avoid carbon dioxide pockets. The oro-nasal pocket must be a snug fit to the diver’s face, and the helmet liner/snoopy should substantially fill the void within the helmet.
● The neck dam must fit snug and not leak or ‘burp’ gas. Loss of gas would result in breathing loop volume and contents fluctuations that can be difficult to manage. Latex or silicone neck dams, as opposed to neoprene, can be favorable for this reason.
● The faceplate must be thoroughly defogged before diving. Use of diluent gas in a steady flow to defog the mask will result in fluctuating (dropping) pO2, and thus excessive gas use to stabilize pO2. Defogging using gas flow should be kept to a minimum. Small magnetic wipers can be an effective and alternative defogging tool.
● The helmet itself must provide a means to evacuate water and release an over-pressurization of gas during ascent. While an OPV within the breathing loop will dump gas from the loop, manual dumping via a valve at the helmet provides for diver control when bailed off loop. The chin is an effective location given that it is a low spot and permits water evacuation.
● Rolling maneuvers are difficult with a helmet, so a means of water evacuation of the exhalation hose should be considered. In this case, a manual water evacuation pump may be installed at the exhale breathing hose and/or at the low point in the system where water may tend to accumulate.
● The BOV flapper valve direction should be carefully noted and verified before integrating with a CCR system. Again, we advocate a right to left orientation as described within this text, and this is employed within our REDLINE system.
● Primary gas supplied to the helmet’s side block manifold is via onboard diluent, or via a 3-way ball valve used for diluent gas switches. The helmet’s conventional ‘bailout’ valve provides access to umbilical fed breathing gas, or other banked cylinder array at the diver, depending on the mode utilized. In all configurations, sufficient open-circuit gas supplies must be in place to permit egress from the furthest point (depth/time) of the dive, and redundancies to that supply should be considered since the helmet cannot be removed during the dive.
● All rebreather diluent devices (ADV, BOV, MAV) are supplied by the same diluent that is feeding the helmet. This gas is routed from the helmet side block accessory port to the diluent junction manifold at the diver’s left chest. This prevents any confusion in diluent gas selection.
Note: It is imperative to carefully consider potentially complex configurations needed for mixed-gas diving so as to mitigate confusion which may result in improper breathing mix supplied to the diver.
As a general rule, keep it simple. Intuition tells us that the helmet should be supplied with gas in a manner that is consistent with standard operations for surface supplied diving. Likewise, the rebreather should be configured in a manner that is consistent with rebreather diving. Putting the two together should NOT cause confusion, particularly with diluent gas supply routing.
Operational Modes
Three configurations are possible when integrating rebreathers with a diver’s helmet:
- Full Surface Bailout Integration (Config SB)
- Semi-autonomous with Surface Telemetry (Config ST)
- Fully-autonomous (Config A)
For consistency, each operational mode employs the same diluent side gas distribution through the helmet side block. This is configured in a manner that is consistent with standard surface-supplied diving, so is intuitively operated by divers familiar with surface supplied diving.
| Preserving consistency at the helmet is critical for seamless integration and diver familiarity. |
Full Surface Bailout Integration | Config SB
The most basic configuration incorporates the option of full surface-supplied breathing gas as bailout. In this mode, the rebreather is used as primary life support with the onboard diluent(s) supplying the helmet directly as the primary go-to gas supply for emergency breathing in open-circuit mode. Upon assessing the situation, if a complete bailout from the rebreather is required, opening the standard black bailout knob on the helmet’s right side will supply gas from the surface to the helmet’s regulator in open-circuit mode. In any situation requiring open-circuit bailout, the diver must have the wherewithal to switch the BOV to open-circuit mode. This two-step bailout requirement is not ideal, though the mechanical actuations cannot be avoided.
Note: This configuration must also account for the complete loss or severance of the diver’s umbilical. Care must be taken to assess risks associated with a severed umbilical or other cause for failure of a surface supplied bailout system. In all instances, it is logical for the onboard diluent supply to be of sufficient volume to return to the surface or to a spot within the ascent profile where additionally redundant surface supplied gas can be supplied.
In the event surface supplied gas is utilized, it is imperative to understand that the helmet will be fed by the supply with the highest intermediate pressure if the bailout valve knob is open. For instance, if the onboard diluent supply is 125 psi and the surface supplied supply is 100 psi, the helmet second stage regulator will draw from the onboard supply until it is completely isolated.
| Any gas supplying the helmet’s side block manifold also feeds the rebreather’s peripheral devices. It is absolutely critical to understand which gasses are supplied to the rebreather diluent feeds, as well as the helmet, and when each should or should not be actuated. Good practice is to supply all peripherals from the same diluent, routing all through a common supply block. |
Semi-autonomous with Surface Telemetry | Config ST
A second and more advanced configuration eliminates the inclusion of surface-supplied breathing gas as a bailout option. In this mode, the rebreather is used as primary life support with the onboard diluent supplying the helmet and diluent manifold. This supply is the primary go-to for emergency breathing in open-circuit mode but is likely not the full volume required for complete open-circuit bailout. The diver must carry all gas required for bailout from the furthest point of penetration (or depth) during the dive, and volumes required may dictate that they are carried, staged, or mobilized on a cart or sled. These techniques are well established by the cave and technical diving community, as well as the tunneling community. This bailout gas is routed to the bailout whip on the helmet side block. It is then important to ensure that the bailout whip is long enough for easy diver actuation as its standard short length is insufficient for this purpose.
While life support is fully autonomous, hard-wired communications and data telemetry (pO2, video, etc.) is maintained to the surface via copper wire or fiber optic tether. Back-up communications must be considered in the event the tether is severed or damaged.
| Surface telemetry for a helmet integrated rebreather includes two-way communications, frequently standard CCTV cameras, lights, and the addition of pO2 data (at a minimum). Analog variants can be mated to a conventional umbilical, though future systems will leverage CAT5 and fiber optic telemetry for digital communications. As both the hardware and data telemetry can become complex, ROV technician level expertise is required on the job site. |
Fully-autonomous | Config A
A third, and the most advanced configuration, also eliminates the inclusion of surface-supplied breathing gas as a bailout option. This configuration further eliminates surface telemetry; the diver is fully autonomous with no surface connectivity whatsoever. Additional consideration must be made for navigation to surface or underwater safe-havens/depots, as well as continuous or intermittent communications to the surface support team via wireless communications or other devices.
This configuration is likely the least desirable from a commercial working perspective but is no different than the autonomous and self-contained conventions used in other diving sectors. In this configuration, the value of using a helmet is somewhat diminished, though added warmth, impact protection, and potentially wireless communication remain value propositions.
This modality has been expanded upon with our Bubble Helmet Presentation System, described in future sections.
Consistency at the Hat is Paramount
In all three configurations described, the diluent and bailout gas supply configurations are consistent at the helmet, meaning the primary diluent uses the same supply inlet as the primary gas supply from conventional surface supplied gas diving. This is to capture the degree of confidence that comes from decades of surface supplied diving standards of practice that are employed routinely by working divers - gas manipulation at the helmet remains intuitive. Unlike self-contained rebreather diving, the helmet cannot be easily removed.
Quite simply, in all configurations:
● The primary diluent gas supplies the helmet through the non-return valve. It may originate directly from an onboard diluent cylinder, or through a 3-way ball valve if diluent gas switches are anticipated.
● The bailout gas is supplied through the bailout knob at the helmet. It may originate from a local diluent gas, banked array, or even the surface through a gas umbilical.
For the latter, if bailout gas is supplied from the surface, a non-return valve must be added in-line with the gas supply, as well as a small overpressure relief valve placed downstream of the non-return valve, but upstream of the black isolation knob. This will prevent hose over-pressurization downstream of the non-return valve upon ascent should the black knob not have been actuated.
The Case for Local Diluent
I am an advocate of using local/onboard diluent as the primary gas supply to the helmet under all circumstances and not using surface supplied gas via an umbilical as the primary diluent, even during dives when a single diluent is used (i.e. no gas switch required). The logic behind this is to enforce the need for carrying a proper bailout supply volume at the diver, just as we do in conventional surface supplied diving. In a worst-case severance or entrapment of the umbilical, the diver must be able to return to the surface in a self-contained manner. This can be completed on the rebreather; however, if further bailout off of the rebreather is required, there must be an adequate supply of open circuit bailout gas available. In effect, triple redundancy is needed when employing these systems.
When umbilical fed, distance to the point of entry or surface is a fixed linear distance, providing a simple egress strategy; however, the time afforded by the rebreather is cause for careful analysis of dependence on self-contained local gas configured through the bailout whip at the helmet since it must be sufficient for required decompression and potentially allow for gas switches during decompression. This necessary gas switch functionality may come from a 3-way ball valve at the diver’s chest plumbed into the helmet’s primary gas inlet. The surface umbilical, used for bailout and plumbed through the bailout whip, is an added safety net only.
With proficiency attained in utilizing this localized bailout strategy, divers can achieve confidence in the Config ST and Config A configurations which allow for full potential of rebreather technology for long linear distance dives free of a bulky umbilical.
| When dived autonomously, without an umbilical, the required bailout gas supply must be sufficient to reach surface or a safe haven. Here, the onboard diluent (vertical AL19 is accessible, though a butt mounted AL50 is the open-circuit bailout gas supply). |
This level of triple redundancy at the diver is common practice in the cave, technical, and decompression diving communities, though not common in commercial diving, and is one of the areas that warrant further consideration as standard practices for implementing these configurations are developed. When using rebreathers for their intended purpose – being range extensions – redundancies, self-help, and autonomy need to be well accounted for, and it would be poor form to start down the path of their use with artificial safety nets rather than ensuring the diver understands the implications of using the technology and how to bail out from it.
New Topside Responsibilities
The marriage of a rebreather with diver’s helmet does not change overall dive team configuration from a regulatory standpoint. A standard 3, 4, 5, or other defined team would carry the same responsibilities topside and meet familiar standby or rescue diver functions. However, attention must be paid to the newly accessible dive profiles and how a rescue might be addressed in practice. The standby diver or other mode of backup intervention should have a means to reach the primary diver, with some contingency, and of course all required support infrastructure and personnel to affect a rescue. This could vary from quite simple to extremely complex pending redundancies in place for both divers.
| Surface telemetry of pO2 can be achieved via serial data transmission, outputting data in a spreadsheet or custom monitoring program. |
One advantage to surface telemetry is a feed of rebreather data, primarily pO2’s from the oxygen sensors, for monitoring and evaluation by the Dive Supervisor. The topside Dive Supervisor must understand the pO2’s displayed, how to recognize a sensor failure, and how to best direct the diver to intervene with a diluent flush or even a gas switch. So, while the responsibility for life system management is removed from the dive supervisor and that onus is placed on the diver, the Supervisor is newly tasked with providing a redundant set of eyes in pO2 monitoring. This data, coupled with video and voice communications, and any other instrumentation data makes the Dive Supervisor act similarly to an ROV Supervisor, and therefore similar technical aptitude is required of a hybrid CCR Supervisor.