Nitrox workshop dings - Divers Alert Network

Rubicon Foundation Archive (http://rubicon-foundation.org)Lang (ed.): DANNUrox Workshop, Divers Alert Network, November 2000C. Recommendations and Conclusions.It is recommended to always use a conservative approach when applying these data.For example, the high contaminant levels found in the four scuba assemblies should, at aminimum, cause users of this equipment to be alert to potential ignition mechanisms.Also, because these contaminants are flammable in most nitrox environments, users shouldtake special precautions to initially clean their equipment and protect their equipment fromcontaminants. It was recommended to the NBL that they disassemble and clean scubaequipment during annual maintenance and maintain component cleanliness as best aspractical during use.Finally, to better evaluate the safety margin or ignition risk in these systems, it isrecommended that testing be conducted to determine if ignition mechanisms other thanadiabatic compression will ignite the contaminants found in scuba assemblies. Alsoneeded is a test to determine how much contaminant is required before ignition occurs byadiabatic compression or another mechanism.Contaminant Ignition Threshold TestsThe results of the tests conducted in both 100 percent oxygen and 50 percent nitrox aresummarized in Table 2.A. 100 Percent Oxygen.For the 100 percent oxygen condition, tests were conducted at pressures of 6.9MPa (1000 psi) and lower, except in the checkout tests with no contaminants, tosimulate one environment found in the NBL breathing-gas delivery system. Reactionswere observed at pressures as low as 5.2 MPa (750 psi) and contaminant levels as lowas 110 mg/m 2 (10 mg/ft 2 ). No contaminant ignitions were observed at 3.4 MPa (500psi), even at contaminant levels as high as 1080 mg/m 2 (100 mg/ft 2 ). Generally, theignition frequency increased with increasing pressure and contaminant concentration.Figure 1 shows a typical data trace for a no-ignition test run at 6.9 MPa (1000psi). Pressure traces of three different impacts and the corresponding photocell outputrepresent only the "fast" data collected at a 1 ms sampling rate for the first second ofeach impact. After the first second of each impact, the data were then recorded on aseparate channel at a 50 ms rate. The photocell baseline, when sensing no light, wasabout 1700 mV. Figure 1 shows that no light emissions were detected by thephotocell for any of the three impacts. During an ignition event, the photocell dataparalleled that of the pressure transducer, though with a slight delay, and peaked atlevels of between 3500 and 5000 mV. The photocell read 5000 mV maximum whencompletely saturated with light.All tests for which the photocell peaked between 3500 and 5000 mV wereconsidered "reactions," or evidence of contaminant combustion. The photocell wasthe only method of detecting a reaction in these tests because posttest analysis showedno physical evidence of combustion, such as charring, discoloration, odor, or residuein the stainless tubing, even in heavily contaminated samples. Other attempts to164