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Nitrogen

• Be on the Lookout for an Insidious

Killer!

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Is Nitrogen Toxic?

No

Yes

Maybe?

The MSDS lists Nitrogen as a simple asphyxiant. But is

it really so simple?

It makes up 79% of the air we breathe.

The body and brain do show symptoms when exposed

to nitrogen at increased pressures and concentrations.

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Are there any Divers in the group?

Nitrogen Narcosis - Rapture of the Deep

Produced by the effects of nitrogen under pressure.

It becomes common among divers descending to

depths greater than 200 feet.

The causes of nitrogen narcosis are not completely

known.

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Nitrogen Narcosis - Symptoms

Depending on depth, symptoms range from

• mild impairment of physical skills,

• impaired reasoning and euphoria

• laughter and giddiness

• severe impairment of reasoning and ability to

respond to stimuli such as hazards

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So why should we care about nitrogen narcosis?

We’re not going to be SCUBA diving in the plant!

The effects of reduced oxygen content due to nitrogen replacement are similar to

nitrogen narcosis caused by breathing air at increased pressures while diving.

Your ability to recognize and respond to hazards will be impaired if the air you breath

has too much nitrogen in it and not enough oxygen!

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Why do you breathe?

More specifically, your desire to inhale air is a

physiological response to what?

You do not breathe in response to a lack of

oxygen in your blood!

You breathe in response to a sensor in your brain

detecting high levels of Carbon Dioxide in the

blood.

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So What! Low oxygen, high CO2, what’s

the difference? I’ll still breathe.

Not necessarily.

If you breathe a mixture of air and nitrogen

that is low in oxygen, your breathing rate

will not necessarily increase enough to keep

your brain oxygenated.

And since nitrogen is colorless and odorless, you

can’t tell when you’re at risk!

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Even more frightening, if you take a breath of

straight nitrogen, it could be your last!

Taking a breath of nitrogen isn’t like holding your

breath. When you hold your breath, the CO2 level

builds until you cannot resist the urge to breathe again.

If you breathe nitrogen, you exhale your CO2 and

your body has no response mechanism to stimulate the

urge to take the next breath.

You could suffocate in the fresh air after one

breath of nitrogen!

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So now that your respect for nitrogen is

appropriately high, let’s put it into perspective.

In the open air, natural air circulation dilutes even

large nitrogen flows to an acceptable level in just a

few feet.

Let’s look at some examples:

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This plot represents a 24” manway with nitrogen blowing out vertically at 18

ft/sec. Our normal purge rate is 1 ft/sec. The blue represents the outer bounds

of slight impairment. Green represents a range where loss of consciousness

becomes certain.

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This plot represents a nitrogen hose blowing at a high rate.

Blue represents impairment and green represents certain loss of

consciousness.

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Buildings or cabinets where air circulation

can be restricted are also a concern.

Take an 8’ x 10’ x 10’ room, it has a volume of 800

cubic feet.

Typical construction practices (without ventilation)

result in 2 air changeovers per hour. 1600 cubic feet

per hour or ~ 27 CFM.

How much nitrogen must flow into the room to impair

a person’s reasoning?

How much to cause loss of consciousness?

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27 CFM Air @ 21% O2 + X CFM @ 0% O2 =

(27 + X) CFM @ 19.5 % O2

X = 2.1 CFM for impairment

27 CFM @ 21% + X CFM @ 0% = (27 + X) CFM @ 10%

X = 30 CFM for unconsciousness

OK, so you can do algebra. What does this mean in real terms?

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2.1 CFM is the rate that would be released

from an open 1/4” tubing line 5’ long

connected to a 1 PSIG nitrogen supply.

This rate could impair your judgement!

30 CFM is the rate that would be released from

an open 3/8” tubing line 5’ long connected to a

17 PSIG nitrogen supply.

You could die if you entered a room with

this leak!

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The Point Is:

In the open air, you have little to worry about

from nitrogen so long as you keep your face

away from locations where it is being vented.

But in areas where ventilation is restricted, you

must be careful of even small leaks!