MBU-20/P, US Navy derivatives, and HA/LP oxygen masks
Updated 29 July 2006
Article on Flightgear On-Line (1)
Article on Flightgear On-Line (2)

Message 22713, 29 Jul 2006
He is wearing the newly approved MBU-20A/P It is basically an MBU-20 with a non-combat edge hose (no tap for the bladder in the helmet) his helmet is the standard 55/P CE though. The mask is basically a USAF HA/LP mask.
Scott

Message 22681, 28 July 2006
That pilot seems to be wearing an Combat Edge (Wombat Edge for our friends Down Under...) You can see the port for the hose on the helmet, but the hose is not present anymore on the mask.
Cheers HUD

Colonel John Forsythe, 49 FW, USAF in an F-117 wearing an HGU-55CE
helmet and MBU-20A/P oxygen mask, 27 July 2006. The picture to the
right is just a close-up of the left picture. © USAF

Message 1308:
Hi DocBoink,
> Fascinating information about the HA/LP modifications (and HGU-55/P mods).
> Not sure whether you were aware of that Combat Edge assembly that Chad
> LeBeau was selling on eBay a few weeks ago?
I have seen it, but my info only came available last week. It is also noteworthy that i have seen several American HGU-55/P's with the commcord plug coming from the right side of the helmet. (while wearing it...). Also we had one pilot wearing a Combat Edge helmet. Only the bladder had been taken out and the port was still in place. He got it that way after training in the States. Further nice feature was the use of the NVG mounts. The small metal brackets are now manufactured at the local airbase metalshop.
> hose exiting the mask assembly on the right side of the facepiece (with the
> exhaust valve on the left).
This is very easy to do, as these parts are changeable.
> This appears to be congruent to the changes you
> stated pilots are advocating to the existing HA/LP mask set-up. Interesting.
The changes are under evaluation and the guy i met ("Devil") will have his mask changed next week.....Bye Ron

Message 1299:
Fascinating information about the HA/LP modifications (and HGU-55/P mods). Not sure whether you were aware of that Combat Edge assembly that Chad LeBeau was selling on eBay a few weeks ago? It was supposedly a special early CE variant assembly intended specifically for F-16 pilots and had the hose exiting the mask assembly on the right side of the facepiece (with the exhaust valve on the left). This appears to be congruent to the changes you stated pilots are advocating to the existing HA/LP mask set-up. Interesting. Cheers, DocBoink

Message 1284:
Hi All, As for oxygen mask fitting to the hose, the metal clamps are forbidden for a long time now (tearing up the hose). After that Ty Rips were used. They are still in use, only the colour has changed. (white to black if I remember correctly). This also having something to do with strenght.
As for the HA/LP (MBU-20/P). Pilots prefer a different setup of the hose/valve assembly. While checking six, the distance between CRU-94/P and helmet, turned out to be not enough to fully turn your head. Talks are going on to replace the hose and valves position, that way the hose will be on the right side of the mask. Closer to the CRU-94/P. Bye Ron

Message 903:
Hi Bluelight14, Thanks for the interesting shot of the Danish F16 jock wearing an MS22001 with Hardman kit suspension. Actually, the MS22001 mask is deemed relatively comfortable by many former users, although the cross piece that is situated at about upper lip level seemed to present some discomfort for those who had moustaches (RAF types, I guess). The MBU-12/P (and its USN variants) was developed specifically to provide greater wearer comfort, improved downward peripheral fields of vision, and substantially enhanced face-seal for high pressure/high-G situations. Imagine the chagrin of the USAF's Aircrew Systems Lab when it performed a study comparing face-sealing efficacy between the original MS22001, the MBU-5/P, and the MBU-12/P, some time ago and found that the vaunted "improved design" MBU-12/P was actually more prone to high-G face-seal leaks at high pressure rates that either the MS22001 or the older MBU-5/P. It is ironic that while the MBU-12/P and its variants are more 'desirable' to collectors (as newer gear), the old MBU-5/P mask actually sealed more completely in many comparative tests. Check out the relatively high value of HGU-55/P and MBU-12/P sets that appear on eBay: they just seem to have a 'sexier' cachet or collector appeal for many people than the old reliable MBU-5/P (that continues to soldier on) attached to an HGU-33/P or HGU-26/P. This was a further incentive to pursue development of the MBU-20/P and HA/LP type masks--a need that conveniently coincided with the initial Air Force TLSS studies carried out in the early 80s. The resulting TLSS system mask-component intended for 'regular flight mode' essentially became the MBU-20/P component of the USAF Combat Edge system (& the HA/LP, which was simply a non-occipital bladder variant intended originally to replace the MBU-12/P in non-ACM applications), after it was decided that the TLSS system was just too costly to field as a complete omnienvironmental protective system for USAF fighter ops. Even further and more recent researches, partial results of which were revealed at one of the Armstrong Lab symposiums, found that the occipital bladder pressure system (which Russia actually pioneered and we adopted) was itself actually not as effective as a proposed developmental mask that had a pneumatic face-seal system built into it; the problem with this last proposal was that it was unnecessarily complicated, the face-seal bladder was found difficult to maintain (similar to the problems encountered with the British S-6 NBC respirator, which was otherwise a superior NBC respirator), and it posed some unforeseen downward vision deficits as well. Of further interest is that the wide variation on facial oro-nasal profiles found among American aviators (due to a diverse blend of racial identities, ethnicities, backgrounds, etc) offered up further difficulties in making the face-seal bladder system effective; it was found to work somewhat better, however, than the occiput pressure system that forced a semi-soft face-cup into the face firmly, in order to achieve adequate sealing in high-G (and at high pressure rates in 'demand' mode). The old MS22001 is not entirely old fashioned and ready for the life support trash heap, as a consequence, and still finds many today who favor it. Again, however, facial conformation characteristics of each pilot dictate which is the best mask for the pilot in question and the mask that is the 'best' one is the one that most effectively fits the unique contours of your face. The British (is that a faint cheer I hear in the background?) actually contributed substantially to the latest American design (MBU-20/P generation) with their P & Q series masks and the RAF studies that produced them; these late 50s and 60s masks cover only the immediate oronasal area, achieving substantial sealing through use of a smaller face-cup with which it is easier to distribute pressure around the edges (especially with a reversed seal contact area), thereby better controlling the leak possibilities. (No American life support researcher would ever admit this, I would venture to opine.) The MBU-20/P mask mimics this approach, even down to its reinforced polymer exoskeleton. At any rate, there is no such thing as a 'perfect 02 breathing mask' for aviators; R&D specialists who are constantly trying to achieve a better face-seal in whole-face NBC masks are another group who are well aware of the difficulties implicit in achieving this goal. (Interestingly, the Finns are spared some of the facial physiognomy problems other nations must devote extra attention to, due to their having a fairly uniform facial contour--lucky Finns!). Cheers, DocBoink

Message 645:
Hi all, Came accros this NAVAIR publication. Gives us in insight on the MBU-5/P replacement with the MBU-23/P. Also take a look at the prices qouted.........(Okay they include UPS shipment.....) Bye Ron

MBU-23/P Procurement AuthorizationADMINISTRATIVE MESSAGE

ROUTINE

R 031125Z MAR 00 ZYB

FM COMNAVAIRWARCENACDIV PATUXENT RIVER MD//4.6.1.2//

TO COMNAVAIRSYSCOM PATUXENT RIVER MD//5.OD43//
CNATRA CORPUS CHRISTI TX//N42//
COMNAVAIRPAC SAN DIEGO CA// N4/N42/N421/N421I//
COMNAVAIRLANT NORFOLK VA//N4/N42/N421/N421A3//
COMNAVAIRESFOR NEW ORLEANS LA//N4215//

INFO CG FOURTH MAW//FAILSAFE//
NATTC PENSACOLA FL//107//
COMNAVSAFECEN NORFOLK VA//122//
NAVOPMEDINST PENSACOLA FL//06//
DSCP PHILADELPHIA PA//JJJ//
DSCR RICHMOND VA//JJJ//
NAVCLOTEXTRSCHFAC NATICK MA//JJJ//
NAVICP PHILADELPHIA PA//JJJ//
NAVOPMEDINST DET EAST NORFOLK VA//JJJ//
NAVOPMEDINST DET WEST SAN DIEGO CA//JJJ//

UNCLAS file://N13523//

MSGID/GENADMIN/NAWCAD PAX RIVER//

SUBJ/MBU-23/P OXYGEN MASK PROCUREMENT//

REF/A/DOC/NAVAIR/15APR99//
NARR/ REF A IS NAVAIR CHANGE CONTROL BOARD NUMBER 991-0172 OF 15 APRIL 1999//
POC/ROBERT FELKAMP/CIV/NAWCAD 3.1.4.3/LOC:PAX RIVER/TEL:301-342-9239 /TEL:DSN 342-9239//

RMKS/1. RESPONSIBLE CODE: NAWCAD PAX 3.1.4.2, EMAIL:
FELKAMPRB@N...

2. REF (A) AUTHORIZES THE REPLACEMENT THROUGH ATTRITION THE MBU-5/P OXYGEN MASK WITH THE MBU-23/P SERIES OXYGEN MASK AND AUTHORIZES USE OF THE MBU-23/P AS OPTIONAL EQUIPMENT IN PLACE OF THE MBU-12/P AND ITS VARIANTS.

3. EFFECTIVE IMMEDIATELY, THE MBU-23/P IS AVAILABLE FOR PROCUREMENT TO ALL USERS OF THE MBU-5/P AND MBU-12/P AND ITS VARIANTS.
NOTE: THE MBU-23/P IS NOT AUTHORIZED FOR USE WITH THE CRU-82P OXYGEN REGULATOR.

4. IN A COST REDUCTION EFFORT, THE NAVAL AIR WARFARE CENTER AIRCRAFT DIVISION PATUXENT RIVER ALONG WITH GENTEX CORPORATION HAVE ESTABLISHED A DIRECT VENDOR-TO-FLEET PROCUREMENT METHOD FOR THE MBU-23/P OXYGEN MASK VIA THE GENERAL SERVICES ADMINISTRATION (GSA) SCHEDULE.

5. NOTE THE FOLLOWING SPECIAL CONSIDERATIONS PRIOR TO ORDERING:
A. THE MBU-23/P MASK COMES WITHOUT COMMUNICATIONS HARDWARE. COMMUNICATIONS HARDWARE MUST BE PROCURED SEPARATELY THROUGH NAVY SUPPLY CHANNELS.
B. USE OF THE MBU-23/P REQUIRES HELMET VISORS COMPATIBLE WITH THE MBU-23/P PROFILE IN ORDER TO MAINTAIN PROPER HELMET/MASK INTERFACE. TRACK AND BUNGEE-MOUNTED VISORS FOR USE WITH THE MBU-23/P OXYGEN MASK ARE AVAILABLE THROUGH OPEN PURCHASE FROM GENTEX.

6. SPARE AND REPAIR PARTS FOR THE MBU-23/P ARE AVAILABLE THROUGH NAVY SUPPLY CHANNELS WITH THE EXCEPTION OF THE OXYGEN DELIVERY HOSE, PART NUMBER G010-1025-01, AND THE GUIDE CABLE MASK PART NUMBER G012-1035-02. AS A PROCUREMENT OPTION GENTEX IS MAKING AVAILABLE TO THE FLEET VIA OPEN PURCHASE ALL MBU-23/P REPAIR PARTS IDENTIFIED IN THE NAVAIR 13-1-6.7-3. ORDERING INSTRUCTIONS AND A PRICE LIST WILL BE INCLUDED WITH ALL SHIPMENTS OF THE MBU-23/P MASK.

7. THE FOLLOWING PROVIDES ORDERING INFORMATION FOR THE MBU-23/P OXYGEN MASK.
A. GSA SCHEDULE NUMBER: GS-07F-0175K
B. GENTEX ORDERING INFORMATION:
GENTEX CORP HOURS: 7:00 A.M. TO 4:00 P.M. PST, MONDAY THRU FRIDAY.
PHONE: (909) 481-7667 (ASK FOR THE MBU-23/P ORDER DESK.)
FAX: (909) 481-7759
ON FAX SUBJECT LINE WRITE: "ATTENTION: MBU-23/P ORDER DESK."
EMAIL: SALESDEPT@G...
ON EMAIL SUBJECT LINE WRITE: "ATTENTION: MBU-23/P ORDER DESK."
C. INDICATE QUANTITY REQUESTED, PART NUMBERS AND PRICE:
G010-1314-21 MBU-23/P MASK, SMALL NARROW $424.48*
G010-1314-22 MBU-23/P MASK, MEDIUM NARROW $424.48*
G010-1314-23 MBU-23/P MASK, MEDIUM WIDE $424.48*
G010-1314-24 MBU-23/P MASK, LARGE WIDE $424.48*
GW9352-01 TRAC VISOR, CLEAR $48.00*
GW9352-02 TRAC VISOR, NEUTRAL GRAY $48.00*
GW9142-01 BUNGEE VISOR, CLEAR $62.00*
GW9142-02 BUNGEE VISOR, NEUTRAL GRAY $62.00*
*PRICE INCLUDES STANDARD SHIPPING COST (UPS GROUND).
D. INDICATE METHOD OF PAYMENT:
1. CREDIT CARD: VISA OR MASTERCARD. PROVIDE CREDIT CARD NUMBER, NAME ON CARD, EXPIRATION DATE, PHONE NUMBER
2. PURCHASE ORDER: P.O. NUMBER, BUYER'S NAME, AND PHONE NUMBER
E. INDICATE METHOD OF SHIPMENT:
1. STANDARD: UPS GROUND IS INCLUDED IN ITEM PRICE.
2. EXPEDITED SHIPPING: $50.00 EXTRA PER ORDER.
F. INDICATE SHIPPING ADDRESS:
FOR INTERNATIONAL SHIPMENTS, LIST APO/FPO ADDRESS.
STANDARD DELIVERY TIME: 5-7 DAYS AFTER RECEIPT OF ORDER.
EXPEDITED DELIVERY TIME: 2 DAYS AFTER RECEIPT OF ORDER

8. IN THE EVENT DAMAGED OR DEFECTIVE ITEMS ARE RECEIVED, CONTACT GENTEX CORP: PHONE (909)-481-7667, FAX (909) 481-7759, E-MAIL
SALESDEPT@G...

9. ANTICIPATE THAT PROCUREMENT OF OXYGEN MASKS, VISORS, AND ASSOCIATED PARTS WILL SOON BE AVAILABLE THROUGH THE GENTEX WEB SITE (E- COMMERCE). WEB SITE ADDRESS: WWW.GENTEXCORP.COM.

10. POINT OF CONTACT FOR THIS MATTER IS MR. ROBERT FELKAMP, NAWCAD 3.1.4.3. DSN 342-9239, COM 301-342-9239, EMAIL FELKAMPRB@N...

11. TYCOMS PLEASE PROVIDE WIDEST DISSEMINATION OF THIS MESSAGE TO ALCON. //

BT

Message 269:
No info at this end on the MBU-21/P, unfortunately. Looks as if the HA/LP concept caught on with the Euro community for its obvious advantages in field of vision, low COG/low weight loading factor, etc., while the CE was a USAF-pushed 'compromise' prompted principally by funding concerns. It is significant, I think, that the HA/LP is surfacing in substantial numbers in Europe, as the HA/LP mask constitutes a relative scarcity on the collector market here in the USofA. The 'biochemical' allusion (mentioned by Steve) may stem from a vague awareness on the part of some that both the TLSS and HGU-51/P systems shared many similarities in program objectives, and that they incorporated NBC protection into those objectives as an important part of the whole concept. One of the findings of the TLSS program, of course, was that a 'one system does it all' concept was by nature not fully satisfactory in every intended parameter. This idea evokes memories of former Viet era Defense Secretary McNamara's near-disastrous TFX aircraft proposal of the 60s (that ironically ultimately produced the EF-111 and FB-111, two of the finest dedicated aircraft systems in the air until recently, and still largely unmatched by any equivalent system in the air today). On the other hand, none of the NBC aviation systems either tested or in actual use today are completely satisfactory and have a relatively short service life due to the wear and tear factors that degrade materials used. In particular, face visor to hood seals problems and weakness, proofed material wear factors, and flex dynamics of these materials dictate a short 'safe service life'. This accounts for the number of MBU-19/P and TAER assemblies that are starting to show up in the US as well as the British AR-5 assemblies (UK equivalent, albeit somewhat different), and undoubtedly for the Russian KM-35i variant Type T NBC mask assemblies, also (examples of which have just started to appear on the collector circuit). The original problem of how to adequately achieve high levels of physiological protection against effects of altitude, G- forces, and chemical/biological threats remains essentially as perplexing today as it was originally, when first seriously addressed by TLSS studies in the 80s. This is not, however, a fact that any aerospace life support defense R&D analyst would likely be inclined to admit, I would be willing to wager. The only happy coincidence at present is that the threat of NBC weapons used by a major international military 'player' is presently very minimal, hence making this unhappy fact somewhat less urgent than it would be if Russia was still a formidable and well-prepared 'cold war' antagonist. As a side note: The cooperative USAF/US Army HGU-15/P NBC clam-shell study of the 60s was, of course, a very, very early attempt to protect aviators merely against altitude effects and NBC threats; there was no incorporation of anti-G protection in the system and the helmet was a stand-alone component of no overall greater system. The TLSS and HGU-51/P systems were truly that--systems. I too would be interested in hearing from anyone who has information on the MBU-21/P, as I have none here on it. That is a great illustration, by the way, provided by Sven, of the HGU-86/P and MBU-22/P combination proposed for use with the unique molecular-sieve oxygen generation system engineered for use in the F-22 program. Steve: although I have no documentation to back it up, I would tend to agree with the theory that the USAF was offered the HA/LP and declined to standardise, opting instead for the MBU-20/P CE mask as being more compatible with both USAF life support aims and existing HGU-55/P system equipment (budget constraints, again). I also agree that the foreign view is perhaps that the HA/LP system was used far more extensively here than it actually was. The presumed reality seems to suggest that HA/LP was used on a limited trial basis only in the US and that it was never used extensively at any time by US air forces (still...starting bids of $399 for one on eBay DO seem a bit steep, wouldn't you say....notwithstanding the relative rarity of the mask over here?). Cheers, all...... Chris

Message 268:
To all: Armstrong Aerospace Symposium of 12/95 proceedings contains a wealth of information on the evolution of these various current helmet and mask developments. All basically stem from the early TLSS program, much of which drew heavily from British counterpressure vest/jerkin concepts of the 60s (Taylor, M.L. Aviation, et al). Budgetary constraints just being felt by US military forces in the 90s resulted in the TLSS's progeny, the ATLSS being rejected by USAF (as too costly), with the CE assembly being established as a reasonable compromise (and far less costly). The ATLSS was then produced in limited quantities for several European Air Forces, while the US went with the CE system (in its many permutations). The 12/95 Armstrong proceedings contains an incredible amount of information on the important TLSS program developments and also dwell extensively on the F-22 Raptor program life support requirements (the main purpose of the 12/95 symposium). The MBU-22/P mask was designated as the target F-22 assembly, mated with the HGU-86/P helmet. The MBU-22/P incorporates a radical new face sealing bladder that is integrated into the faced seal design, as contrasted to the conventional occipital sealing bladder design used in the CE; outwardly, the MBU-22/P bears a striking resemblance to the HA/LP and MBU-20/P masks, for obvious reasons. One bit of intuitive awareness that soon surfaces in the mind of anyone who seriously follows design and development evolution at the present time, is that a complete TLSS assembly (helmet, suit, PLSS, mask, PLZT, etc.) is an important part of the story. There were reportedly less than 55 of the TLSS prototypes manufactured, making them among the rarest of the rare, pivotal bellwether assemblies from whence most of the current developments sprang. As such, the TLSS is far rarer by several orders of magnitude than the already rare and currently coveted HGU-51/P assembly. A promotional illustration of the TLSS (note similarities to complete HGU-51/P system) is attached, for the benefit of those interested in this critically important program of the mid-80s. Anyone interested in definitive information on the TLSS and its spawn would be well advised to try to obtain a copy of the referenced Armstrong Symposium proceedings of 12/95. This invaluable work also has other irreplaceable data on pressure suit and high altitude life support developments. Christopher T. Carey

Message 267:
Love the stuff on the MBU-22/P. Anyone know what an MBU-21/P is? The person I talked to about the MBU-22/P said he "thought the mask was a bio-chemical mask" but wasn't sure. Chris, I had no reference to the HA/LP connection to the CE, I was reading between the lines ie the CE is similiar to the HA/LP and I'll run through the TLSS stuff again. My main point on the HA/LP was that I don't think the US military really used the HA/LP and Gentex had it around for a awhile trying to sell the idea. I am interested in what "Current issue" masks the US Air Force is flying. I think the international community may have adopted the HA/LP possibly in tandem with the Gentex supplied HGU-55/P helmet and many may have assumed the mask was used in the States. Also for Chris: Awhile back, I sent you a picture from a book on the F-22 by Sweetman. The caption on the picture states the helmet is an HGU-86/P (Part of a Boeing developed life support system). Is the mask in this picture the MBU-22/P? Cheers all, SteveN

Message 266:
Hello Steve and all, I think this HA/LP has been tested by the Royal Netherlands Airforce as a replacement for the MBU-12. But it differs a bit with the normal HA/LP and MBU-20/P. The microphone assembly and the straps are different. So maybe this mask is an early version of the HA/LP MBU-20/P line masks or it's a prototype? About the MBU-22/P: This is what I have found about it in a brochure of the ALPHA helmet from Helmet Integrated Systems LTD. The brochure tells me that this mask is a MBU-22/P which is designed for the F-22 aircraft. I have contacted Gentex about it but they told me the MBU-22/P is not manufactured by Gentex and they think it's not an Mil. Spec. Oxygenmask. Here you can see a picture of it. It has the same microphone connector as the HA/LP from my question but this mask has a kind of chinstrap. The mask is shown at the ALPHA HGU-86/P helmet assy. Cheerio, Sven

Message 265:
Sven,
I have some information from Gentex dated 1986 on the HA/LP-PPB (High Altitude/Low Profile Positive Pressure Breathing Oxygen Mask. At the time (1986), the HA/LP-PPB mask was being marketed as a replacement for the MBU-5/P, the MBU-12-/P and the MBU-14/P through MBU-17/P oxygen masks. It was compatible with the HGU-26/P, HGU-33-34/P, and the HGU-55/P flight helmets, but the visors would have to be trimmed to match the HA/LP-PPB mask profile.
HA/LP-PPB features.
1- Separate inhalation and compensated exhalation valves for ease of breathing
2- Comfortable low profile silicone rubber faceseal.
3- Separate hardshell and faceseal.
4- Side entry hose to bring the mask center of gravity (CG) close to the face.
5- Small mask faceseal area which seals on the supramentale (between the
lower lip and chin rather than under the chin).
6- Improved downward vision.
7- Useful up to 60,000 ft.
8- Appears to be a Gentex Design

Note that the mask did not offer an occipital bladder valve or connection.
Here's where I'll get in trouble with all the collectors who have purchased the HA/LP masks on the internet and all those folks who say "Never say never".
The Combat Edge (HGU-55/P CE ) program used the HA/LP as a starting point and ended up with the MBU-20/P complete with the occipital bladder. The Navy has two versions (MBU-23/P without the occipital bladder and the MBU-24/P which is nearly identical to the MBU-20/P). The MBU-23/P is a replacement for the MBU-14-/P through MBU-17/P masks in non-high G environments while the MBU-24/P is for use in high G environments.
Given that the MBU-18/P and the MBU-19/P are known bio-chemical masks and the MBU-20/P is the CE mask, it would be safe to say that the US military did not fly the HA/LP mask as such (other than in testing). In order to procure the HA/LP mask, there would have to be an MBU type designation assigned and there aren't any available. My information indicates that the MBU-21 and MBU-22 are not oxygen masks, but I can't confirm this at the present time. My guess is that the USAF would use the MBU-20 both with and without the occipital bladder and still call it an MBU-20/P. The US Navy has a tendency to assign a new type designation for minor modifications.
The HA/LP mask doesn't fit into the chronology of US flight equipment as an operational mask. It is possible that exceptions were made but the HGU-55/P CE program seems to have addressed all the things the HA/LP was supposed to do. I'd love to see any documentation to the contrary as I am most anxious to learn. I should point out that the HA/LP mask could have been accepted and standardized by other nations and used. I notice that a lot of HA/LP masks seem to be surfacing in Europe.
As stated earlier, this is my best guess based on what I know about US military procurement policies. I am waiting for information from my contacts in USAF life support on the operational aspects of the MBU-20/P and HA/LP. So maybe this will all change. Cheers, Steve N

Message 264:
I have a question to you experts: Can someone tell me more about this HA/LP version? The mic connector differs a lot with the 'normal' HA/LPs I have seen. Also the way the straps for the Bayonet receivers are connected to the hardshell differs. It this HA/LP an earlier version or maybe a prototype? Label on this mask says: MASK, OXYGEN HA/LP-PPB SIZE: LARGE PN G010-1030-03 U.S. PAT NO. 4,677,977 Hope someone can help me out. Best regards, Sven Scheffers