Dave Dalton was kind enough to post a Nasa/Johnson Space Center study on 
regulator contamination to his website. The original links are below.  
The test was done at White Sands and concluded that even dirty, non-02 
cleaned regs were safe to use with mixes up to 50% oxygen. Although this 
test was performed with 50% O2 and not 100%, I thought it worth posting 
to the list to put the issue of O2 cleaning in perspective.

>
>http://home.quixnet.net/~dmdalton/nasa.htm
>
>or if you want to see the version with the signatures you can see it at
>http://www.dnax.com/
>
>look under the link for Nitrox Research.

-----


Document no: TR-900-001

December 22, 1997 

Component Testing and Clean Verification of SCUBA Equipment for the NASA 
JSC

Neutral Buoyancy Laboratory

Lyndon B. Johnson Space Center

White Sands Test Facility

P.O. Box 20

Las Cruces, NM 88004

(505) 524-5011
     

Abstract

The NASA White Sands Test Facility was requested by NASA Johnson Space 
Center (JSC) to perform component testing and clean verification on the 
self-contained underwater breathing apparatus (SCUBA) diving equipment to 
be used in the JSC Neutral Buoyancy Laboratory (NBL).

The NBL facility requires divers to breathe a nitrogen/oxygen (NITROX) 
gas mixture with an oxygen concentration ranging between 2 I and 49 
percent. The increased oxygen concentration warrants testing of the 
apparatus in its worst-case use environment to evaluate potential 
ignition mechanisms. Three SCUBA equipment assemblies were tested, and 
included a first-stage regulator with flex hoses to two second-stage 
regulators, a submersible pressure gauge, and a buoyancy control device. 
Sixty pneumatic impact cycles were performed at 20.7 MPa (3000 psi) in a 
50-percent NITROX gas mixture on each of the three test articles. Each 
test article passed the impact test with no failures or evidence of 
ignition, The clean verification indicated that gross amounts of 
particulate and non-volatile residue were present in the oxygen-wetted 
portions of the assemblies.

1.0 Introduction

WSTF was requested by NASA Johnson Space Center (JSC) to perform 
component testing and clean verification on the self-contained underwater 
breathing apparatus (SCUBA) diving equipment to be used in the JSC 
Neutral Buoyancy Laboratory (NBL}. The component testing and clean 
verification were performed in response to recommendations made by an 
earlier oxygen hazards analysis of the JSC NBL SCUBA equipment (Forsyth 
1996).

2.0 Objective

The objective of the component tests was to determine the susceptibility 
of the NBL SCUBA equipment to ignition by pneumatic impact in a 
50-percent nitrogen/oxygen (NITROX) mixture at worst-case operating 
conditions. The objective of the clean verification was to determine the 
approximate clean level of the oxygen-wetted portions of the SCUBA 
assemblies.

3.0 Background

The JSC NBL facility will require divers to use a special NITROX gas 
mixture instead of conventional breathing air in their cylinders. 
Conventional breathing air has an oxygen concentration of approximately 
21 percent; it ranges between 21 and 49 percent for the NITROX gas 
mixture. Previously, WSTF had performed an oxygen hazards analysis on 
this SCUBA equipment to consider the materials flammability and potential 
ignition mechanisms with the new gas mixture (Forsyth 1996).

The SCUBA equipment analyzed in the oxygen hazards analysis included an 
oxygen cylinder, an oxygen cylinder valve, a first-stage regulator, a 
second-stage regulator, a submersible pressure gauge, and a buoyancy 
control device. The analysis recommended that component testing be 
performed on the first-stage regulator and downstream assembly, at 
worst-case use conditions, to evaluate the equipment's vulnerability to 
ignition by pneumatic impact with gaseous oxygen. The analysis also 
recommended that clean verification be performed annually on a sample 
population of the SCUBA equipment to evaluate the cleanliness level.

4.0 Approach

The approach for the component tests was to randomly select four SCUBA 
assemblies that had been in service for approximately one year from the 
JSC Weightless Environment Training Facility. These assemblies were 
delivered to WSTF for testing and evaluation.

The test articles were placed in a test fixture to secure them for impact 
and then allow for a remote venting of the test article. Each component 
assembly was tested individually in its use configuration by rapidly 
impacting the first-stage regulator for 60 cycles at the worst-case 
operating pressure. Three component assemblies were tested by pneumatic 
impact to assess the repeatability of the data.

Clean verification tests were performed on four SCUBA assemblies. The 
assemblies were functionally checked, disassembled, sampled for 
particulate and non-volatile residue (NVR), and re-assembled. The SCUBA 
assemblies were then returned to the customer.

5.0 Experimental

5.1 Test Articles

The SCUBA assemblies tested were the same as those analyzed in the 
hazards analysis, excluding the oxygen cylinder and oxygen cylinder 
valve. The assembly included a first-stage regulator, two second-stage 
regulators, a submersible pressure gauge, a buoyancy control device, and 
their connecting flexible hoses (Figure 1). A summary description of the 
test articles is shown in Table l.

Only three of the assemblies were tested by pneumatic impact (SCUBAs 2, 
3, and 4). The fourth assembly, SCUBA 1, was a demonstration unit but was 
included in the clean verification tests. The demonstration unit was the 
only assembly that was ultrasonically cleaned before shipping. In three 
of the assemblies, NITROX 0-ring kits were installed in the regulators 
before delivery to WSTF (SCUBAs I, 3, and 4). These kits had Viton® 
0-rings. In the other assembly (SCUBA 2), no pretest preparation was 
performed; the original 0-rings were left installed, and the assembly was 
not cleaned before shipping.

Table 1

Summary Description of SCUBA Test Articles

First Stage Second-Stage Second-Stage

Name Regulator Regulator 1 Regulator 2 0-Rings Clean

SCUBA Mares MR 12 III Mares MR 12 III Mares MR l2 III NITROX Ultrasonic

1 S/N 651378 S/n W29S/N W30 

07168648 08036509

SCUBA Mares MR 12 Mares MR 12 Mares MR 12 III Standard None

2 DFC S/N E70335 Navy S/N 06204829

S/N 513713

SCUBA US Divers US Divers US Divers NITROX None

3 Conshelf 21/22 Conshelf 14 Conshelf 14

S/N ALB0524 S/N B76K2310 S/N JY6K0735

SCUBA US Divers US Divers US Divers NITROX None

4 Conshelf 21/22 Conshelf 14 Conshelf 14

S/N ALB1100 S/N B76K119 S/N JY6K1S57

 

 

5.2 Test Method

The test method used to evaluate these SCUBA assemblies was pneumatic 
impact, or adiabatic compression. When a dead-ended test article filled 
with ambient pressure oxygen is rapidly pressurized, the pressure can 
increase too quickly for the heat of compression to be dissipated to the 
surroundings. Most of the thermal energy generated is contained in the 
compressed gas, resulting in a small slug of hot gas at an elevated 
pressure located at the dead end. In this test configuration, the gas is 
rapidly compressed against the first stage regulator seat, which is the 
"dead-end." In theory, the gas temperature generated by adiabatic 
compression should reach the autogenous ignition temperature of the 
polymer seat material in 100-percent oxygen. However, in this case, the 
first- stage regulator allows flow upon impact, so is not a true 
dead-end. Also, the gas is a 50-percent oxygen concentration, which 
decreases the severity of the test environment.

5.3 Test System

The tests were conducted using a WSTF pneumatic impact component test 
system that simulates a sudden pressurization event such as what could be 
caused by a fast-opening system valve. The fast opening system valve 
allows pressurization rates to the test article of approximately 20 ms 
with system pressures up to 69 MPa (10,000 psi). A VME computer system 
was used to control the pressurization of the test articles during the 
pneumatic impact cycles. The VME software was written to allow computer 
control of the fast-acting impact valve, the vent valve, and the upstream 
isolation valve. Otherwise, all valves were controlled by the test 
conductor. The VME system was also used for data acquisition. Standard 
video recordings were made of all tests. 

A test fixture was designed and implemented to remotely vent the gas 
through the second-stage regulator (Figure 3). A Bimba actuator provided 
a piston to push the vent button on the second-stage regulator, The test 
fixture also secured the SCUBA regulators and flexible hoses and provided 
a mount for the test article pressure gauge so it could be monitored by 
video.

5.4 Test Conditions

The test conditions were chosen to closely simulate the actual 
application. A 50-percent NITROX

gas mixture was used in all tests. The pretest temperature was ambient. 
The test pressure up to the

first-stage regulator was from ambient to maximum use pressure, 20.7 k 
0.7 MPa (3000 k 100 psi).

The pressurization time to the first-stage regulator was consistent at 
approximately 20 ms.

 

 

5.5 Procedures

5.5.1 Pneumatic Impact Tests

The test articles were treated as clean hardware while at WSTF. Latex 
gloves were used in handling the test articles at all times, and each 
component was double bagged to maintain clean whenever the test articles 
were not in the test system.

The test articles were inspected prior to installation in the test 
system, and any anomalies were noted. The test article was then mounted 
and secured in the test fixture. The first stage regulator was connected 
to the system's test article interface (Figure 3). An aluminum blast 
shield and cinder blocks were placed around the test article to protect 
the test system from damage.

After installation, the test article was leak checked with gaseous 
nitrogen (GN2). The vent on one second-stage regulator was then opened, 
and the test article assembly was purged with low pressure NITROX to 
adequately displace the GN2, The vent was then closed, and the system was 
pressurized up to the fast-acting isolation valve with NITROX at test 
pressure. The data acquisition and video equipment were then started. 
Upon command, the software opened the fast-acting valve, creating a rapid 
compression on the first-stage regulator, followed by a lower-pressure 
surge to the second-stage regulators, The pressure was held for 
approximately 18s to determine if leaks were present, indicating a 
possible ignition. Ignition was also determined by a flash on the video 
or by an audible report. If no reactions or failures were evident, the 
pressure was vented through the second-stage regulator vent and upstream 
of the first-stage regulator, and the test article was impacted again. A 
total of 60 pneumatic impacts were performed on SCUBAs 2, 3, and 4.

5.5.2 Clean Verifications

First, a functional check was performed on each SCUBA assembly by 
pressuring the assembly up to its maximum operating pressure with GNp and 
recording the pressure decay over 5 min. The SCUBA assemblies were then 
carefully disassembled to the piece-part level in a Class 100 flowbench 
to ensure cleanliness was maintained before flushing, Only the 
oxygen-wetted pieces of the assemblies were tested for cleanliness. The 
metal pieces were separated from the polymer pieces prior to flushing, 
and different procedures were used for the metal and polymer pieces. All 
metal pieces were flushed with CFC l13, and both particulate and NVR 
samples were evaluated. All polymer pieces were flushed separately with 
distilled water, and only a particulate sample was evaluated. No NVR 
levels were analyzed for polymer pieces because many polymers are 
composed of hydrocarbons that could be released into the sample and 
affect the results. For this reason, the flexible polymer hoses were 
flushed only with water and evaluated for particulate.

The metal pieces of the first-stage regulator that were individually 
flushed included the internal trim pieces, the internal regulator body, 
and the inlet filter. The first-stage regulator soft goods were flushed 
together as one sample. The metal pieces of the second-stage regulators 
that were individually flushed included internal trim pieces and the 
internal regulator body. The second-stage regulator soft goods were 
flushed together as one sample, and the flexible hoses were flushed 
individually.

6.0 Results and Discussion

6.1 Pneumatic Impact Tests

No indication of ignition or failure was observed in any piece of the 
three SCUBA assemblies tested. Even test article SCUBA 2, which did not 
have a NITROX-compatible soft good kit, did not sustain any ignitions. 
There were no flashes or audible reports in any tests, nor did any test 
article leak pressure during the pressure hold phase of the impact cycle. 
In each test, the pressurization rate to the test article was 
consistently 20 ms and the peak pressure was approximately 20.7 MPa (3000 
psi).

Figure 4 shows a pressure vs. time curve for test article SCUBA 1, cycle 
31. The pressure shown was read at the test article interface. This curve 
is typical of all pneumatic impact cycles performed on the three SCUBA 
assemblies. Data recording began before opening the fast-opening valve, 
when the test article pressure is ambient. Upon opening the fast-opening 
valve, the test article pressure reaches its peak pressure and is he1d 
for approximately l8 s before being vented back to ambient pressure. 
Because the first-stage regulator allows flow-through up to its set 
pressure, the upstream pressure bleeds through to the second-stage 
regulators, creating a slow pressure rise after the initial impact. This 
effect is more evident when only the impact phase of the cycle is plotted 
(Figure 5). The initial impact on the first-stage regulator, shown as the 
first pressure peak in Figure 5, consistently reached approximately 19.3 
MPa (2800 psi) during each test, After the initial impact, the pressure 
reached its maximum at 20.7 MPa (3000 psi) after approximately 0.8 s.

Posttest functional checks with GNp showed no anomalies in any of the 
four SCUBA assemblies.

Each assembly allowed minimal leakage over the 5 min hold at 20.7 MPa 
(3000 psi). Data sheets for each assembly recorded the pressure decay on 
two gauges, the test console gauge standard and the first-stage regulator 
gauge of the SCUBA assembly. The data sheets for SCUBAs 1 through 4 are 
included Appendices A through D, respectively.

6.2 Clean Verification Tests

After the functional checks were completed, the SCUBA assemblies were 
disassembled for the clean verification tests. The particulate level and 
NVR quantity data for the piece parts of the first and second-stage 
regulators and connecting hoses of each assembly were recorded in detail 
on the data sheets in the Appendices. Table 2 summarizes the respective 
particulate and NVR levels for each component of the four SCUBA 
assemblies. The NVR levels recorded in Table 2 are calculated values 
based on the quantity in milligrams (mg) of NVR weighed in the sample, 
divided by the approximate surface area, in square feet (ft2), of the 
component piece(s) flushed. The unit of measure, mg/ft2, was chosen to 
allow easy comparison with data from previously reported literature. The 
surface areas of the component pieces used for calculation are only rough 
approximations and, in most cases, represent larger-than-actual surface 
areas to give best-case, lowest contaminant levels.

The first-stage regulator of each of the test articles was found to be 
highly contaminated in each of the four assembly parts, both in 
particulate and NVR levels. In SCUBA 1, the first-stage regulator parts 
each failed a Level 1000 particulate analysis, meaning that particles 
larger than 1000 pm were discovered in each of these parts after flushing 
(Table 2). The internal metal pieces in SCUBAs 3 and 4 had particulate 
levels higher than what could be counted. The particles were described as 
possibly "Krytox, plastics, metals, glass, and grit" (Appendices C and 
D), In SCUBA 2, the internal metal pieces failed a Level 200 particle 
count, meaning that at least one particle larger than 200 pm was found. 
The analysis did not state if higher particle levels would have been 
passed. The internal soft goods of each test article were flushed 
together, and large particulate was also found. SCUBA 3 had a particulate 
level higher than what could be counted. The inlet filter of SCUBA 2 
passed a Level 300 particle level. No particles larger than 300 pm, and 
an allowable distribution of smaller particles, were found in the filter 
after back-flushing.

NVR levels in the first-stage regulators were also excessive. The 
internal metal pieces of SCUBA 4 showed the lowest NUR quantity of the 
four SCUBA assemblies analyzed, at 49.0 mg/ft2 (Table 2). The body cavity 
NVR data for SCUBA 1 were not listed in Table 2 because of an error 
discovered during the sampling process which invalidated the NVR 
quantity, and the body cavity NVR data for SCUBA 3 were not analyzed. 
However, the YVR quantities for this part in SCUBAs 3 and 4 were very 
similar, at 102.7 mg/ft2 and l 18.7 mg/A~, respectively. The inlet filter 
of SCUBA 1 was back flushed, and a large amount of NVR was discovered, 
equaling 122.2 mg/ft2 Higher contamination levels in the filter were 
expected to a certain extent, because the filter is exposed to the 
outside environment during connecting and disconnecting the SCUBA 
assembly to its gas source. For SCUBA 2, the NVR quantity was 
significantly lower, at 24.4 mg/ft2.

The second-stage regulators of each test article were also found to be 
highly contaminated in each of their assembly parts. Particulate levels 
found on the internal metal pieces of each second-stage regulator failed 
level 750 and above in each test article. The particles were described as 
"mostly metal and fiber" (Appendices). Particulate analysis of the soft 
goods of each second-stage regulator indicated that one sample failed 
Level 300 and one failed Level 500, but the rest failed Level 1000 or 
higher. Similar high levels of particulate were found in sampling the 
second-stage regulator bodies. The particulate in one second-stage 
regulator body was described as "mostly clear and metal chunks and some 
clear fibers" (Appendix C). Some particulate samples from the flexible 
hoses were less contaminated. One flexible hose sample passed Level 200, 
and one passed a level 500. Most other hose samples, though, contained 
large particles. The particulate was characterized as "mostly metal" 
(Appendix C).

NVR levels were taken only for the internal metal pieces of the 
second-stage regulators. These ranged from 150.7 mg/ft2 in Scuba 03 to 
469.2 mg/ft2 in Scuba K. NVR levels were not taken for the second-stage 
regulator bodies because it was difficult to separate the polymer pieces 
from the metals.

 

 

7.0 Conclusions

No ignitions were sustained by the three SCUBA assemblies tested by 
pneumatic impact in a 50 percent oxygen NITROX mixture at 20.7 MPa (3000 
psi). Even test article SCUBA 2, which did not have a NITROX-compatible 
soft good kit, did not sustain any ignitions. Functional tests performed 
after the completion of the pneumatic impact tests confirmed that each 
SCUBA assembly held pressure. The clean verification tests showed gross 
amounts of particulate and NVR in most component parts. Despite these 
high levels of contamination, the pneumatic impact tests demonstrated 
that the component design is robust enough to withstand ignition under 
worst-case NITROX operating conditions. It should be noted, however, that 
the results of this testing do not negate the need to pre-clean systems 
for oxygen service or the need to maintain these systems clean during 
use. Prudent knowledge and practice of oxygen system safety is 
recommended for all oxygen systems, even for those operating in 
50-percent NITROX environments.

 

8.0 Recommendations

It is recommended that each SCUBA assembly be initially cleaned and then 
maintained clean to an acceptable level during annual disassembly and 
cleaning and during intermediate maintenance procedures. The acceptable 
level will be approved by JSC QARSO and Materials Processing personnel.


Best regards --

Bill

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