SAC vs RMV, revisited

[scubadada]

SAC and RMV are both per atm, corrected to surface pressure

 

[stuartv]

I would like to see the breathing rate converted to a surface rate described as SACP or SACV, i.e. Surface Air Consumption Pressure or Surface Air Consumption Volume. RMV is not descriptive enough. It is based on per minute (the M) and volume (the V) but respiratory (R) is superfluous and there is nothing indicating it is a surface rate quantity.

That's because it's not.

It's up to the user to be knowledgeable enough to understand that if you breathe 0.5 cu-ft/min at 33', it's going to be double the number of molecules of gas as if you breathed 0.5 cu-ft/min at the surface. You're breathing 0.5 cu-ft/min either way (at 33' or at the surface).

Once you use the RMV to calculate a specific volume of gas, it's up to you to convert that from (for example) volume at 2ATA to what the volume would be at 1ATA.

I.e. Assume my RMV is 0.5cu-ft/min.

If I hang out at 100', for 10 minutes, I will have consumed 5 cu-ft of gas - AT 4 ATA.

If I hang out at the surface for 10 minutes, I will still have consumed 5 cu-ft of gas - at 1 ATA.

RMV is not a surface rate quantity. It is a rate of volume per minute. Period. The 'R' is not superfluous because it indicates that the rate is referring to rate of breathing - i.e. respiration.

 

[scubadada]

That's because it's not.

It's up to the user to be knowledgeable enough to understand that if you breathe 0.5 cu-ft/min at 33', it's going to be double the number of molecules of gas as if you breathed 0.5 cu-ft/min at the surface. You're breathing 0.5 cu-ft/min either way (at 33' or at the surface).

Once you use the RMV to calculate a specific volume of gas, it's up to you to convert that from (for example) volume at 2ATA to what the volume would be at 1ATA.

I.e. Assume my RMV is 0.5cu-ft/min.

If I hang out at 100', for 10 minutes, I will have consumed 5 cu-ft of gas - AT 4 ATA.

If I hang out at the surface for 10 minutes, I will still have consumed 5 cu-ft of gas - at 1 ATA.

RMV is not a surface rate quantity. It is a rate of volume per minute. Period. The 'R' is not superfluous because it indicates that the rate is referring to rate of breathing - i.e. respiration.

Hi Stuart,

Be clear to folks. At 100 ft you are breathing 2 cu ft/min of gas from your cylinder, not the 0.5 cu ft/min that is your SRMV

Sorry, but for reasons that are not perfectly clear to me, this seems to be a topic that many do not understand.

 

[stuartv]

Hi Stuart,

Be clear to folks. At 100 ft you are breathing 2 cu ft/min of gas from your cylinder, not the 0.5 cu ft/min that is your SRMV

Sorry, but for reasons that are not perfectly clear to me, this seems to be a topic that many do not understand.

I said 5 cu-ft AT 4 ATA. Yes, that is 20 cu-ft at 1 ATA.

As I said, it is up to the user to be knowledgeable enough to understand that. Anyone that had decent, basic OW training should get that.

 

[scubadada]

I said 5 cu-ft AT 4 ATA. Yes, that is 20 cu-ft at 1 ATA.

As I said, it is up to the user to be knowledgeable enough to understand that. Anyone that had decent, basic OW training should get that.

I don't think these concepts are well taught at all on the basic level. Thanks for trying

 

[EFX]

I'd like to see people use units, not confusing groups of letters or acronyms.
You are an engineer; you'd really prefer SACP instead of psi/minute or liters/minute?

SACP can be l/min or psi/min. SACP or SACV is used when describing the surface air consumption when an actual value is not needed. When showing an actual value then units must be given.

Damn near anything is better than saying "my air consumption is 20." At the very least, say whether you mean at the surface or at depth, and do you mean based on pressure or volume. And if you then say, "at the surface, based on pressure," then I still have to ask "what size cylinder?" and "are you working in imperial or metric?" Otherwise, your '20" in meaningless.

You just spent almost 3 sentences in the above quote describing something that could have been said with one acronym. Hah! Funny!

 

[EFX]

That's because it's not.

It's up to the user to be knowledgeable enough to understand that if you breathe 0.5 cu-ft/min at 33', it's going to be double the number of molecules of gas as if you breathed 0.5 cu-ft/min at the surface. You're breathing 0.5 cu-ft/min either way (at 33' or at the surface).

Once you use the RMV to calculate a specific volume of gas, it's up to you to convert that from (for example) volume at 2ATA to what the volume would be at 1ATA.

I.e. Assume my RMV is 0.5cu-ft/min.

If I hang out at 100', for 10 minutes, I will have consumed 5 cu-ft of gas - AT 4 ATA.

If I hang out at the surface for 10 minutes, I will still have consumed 5 cu-ft of gas - at 1 ATA.

RMV is not a surface rate quantity. It is a rate of volume per minute. Period. The 'R' is not superfluous because it indicates that the rate is referring to rate of breathing - i.e. respiration.

stuartv, I'm not as dumb as you think I am. I know how to calculate SAC and RMV and I know what those terms mean. The whole point of my post about using SACP and SACV is to avoid lengthy explanations of vague acronyms like what you're posting above. Of course RMV is not a surface quantity. Duh. That's the problem.

BTW, SAC by itself is vague. Does it mean surface air consumption or surface alcohol consumption?

 

[tursiops]

BTW, SAC by itself is vague. Does it mean surface air consumption or surface alcohol consumption?

Context is everything. Most acronyms and abbreviations are that way.

 

[tursiops]

SACP can be l/min or psi/min.

??

 

[Storker]

Be clear to folks. At 100 ft you are breathing 2 cu ft/min of gas from your cylinder, not the 0.5 cu ft/min that is your SRMV

No. No, no, no. He's breathing 0.5 cu.ft/min. And at 30m those 0.5 cu.ft is the same amount of gas as 2 cu.ft. at the surface.