Metering for the First Responder: Those using the meter the most know the least (Why NFPA 1010 Matters)

You Don't Know What You Don't Know

Introduction

When it comes to metering in the fire service there is a culture of “I’m no Hazmat Technician - meters are for Hazmat geeks.”  Basic metering is a skill first responders must be competent with.  As Technology progresses, engineers continually find innovative ways to use chemicals.  With these technologies threats to first responders increase tenfold.  This article will review the four-gas meter essentials that will help keep first responders safe.

Neither CFR 1910.120, nor NFPA 470 emphasize meter training programs for those who use the meters the most, the first responder.  Now enters NFPA 1010 which now requires basic monitoring training for Firefighters.

This has been a goal so close to my heart and to see it finally get some traction has made it all worth it, this was the driving force behind starting The Meter Guys!

Many Hazmat Operations programs do not provide hands on meter training.  So, let’s review four-gas meter configuration and how the sensors work.  This way you may gain a better understanding of those dreaded meters in your fire apparatus.

The most common four-gas meter configuration is Oxygen (02), Lower Explosive Limit (LEL), Carbon Monoxide (CO) and Hydrogen Sulfide (H2S) sensors.

The most important sensor is the one between your ears doing the interpretation. 

Understanding what the readings mean is essential to your safety and health, vs the culture of waiting for alarms to go off.  This article will focus on the Oxygen and LEL sensors; we will leave the CO and H2S sensors for another day to do them proper justice.

Oxygen Sensor

Oxygen Sensors are one of the most important sensors if not the most important for first responders.  Most meters sensor’s readings are based on normal Oxygen levels in air, including your brain!  If the Oxygen sensor is faulty, all other sensor readings can become suspect.  On start up the meter begins a series of self-checks as it warms up and checks the sensors, alarms, and its calibration status.  Once warm, the Oxygen sensor should read 20.9% for most manufacturers, some are at 20.8% (sensors may drift a little bit 0.1% to 0.2% either way).

After self-checks, a fresh air calibration is needed to establish a baseline atmosphere.

(This is The Meter Guys stance; some manufacturers say the fresh air calibration is not needed if the meter is maintained properly).

This tells the sensors “What you sense now is clean air.” Therefore, it must be done outside, in clean air.  The cab of your apparatus may be contaminated by exhaust fumes, or dirty gear.

(It’s okay to turn your meter on enroute to the call but don’t fresh air it in the cab, cabs are filthy contaminated boxes! Fresh air upon arrival outside away from the exhaust and the flow path of the doorway.)

If your meter displays negative numbers, you likely fresh air calibrated in a dirty atmosphere, or you turned it off with contaminants still in it on your last call.  In other words, the meter had stuff in its sensors when you turned it off, when you turned it on the stuff was gone and the meter then reads negative. Move to clean air and fresh air calibrate again.

The Oxygen sensor has two alarms, low (19.5%) and high (23.5%).  These alarm levels are considered IDLH atmospheres by OSHA.  At 19.5% you should be utilizing your SCBA due to possible toxicity, flammability, or hypoxic hazards. At 23.5% there is an increased fire risk.  Bottom line is if your meter alarms, you need to take action!  Your department’s SOP’s should (I hope) dictate your actions.

The Meter Guys stance is that these numbers should be changed for the Fire Service. Our goal is to get you to mask up as soon as you see your O2 sensor deflect on a call! Read below to understand our reasoning behind this statement.

Let’s look at the reading of 19.5% Oxygen.  Air is 1/5^th Oxygen (approximately).  1% Air = 10,000 ppm (parts per million), x 1/5^th = 2000 ppm of Oxygen, and the other 8000 ppm mostly Nitrogen.

Yes, there are a few other things in the air, but we need to be firefighter focused not lab rat focused!

If the Oxygen level drops 1% this means 10,000 ppm of Oxygen, and 40,000 ppm of Nitrogen have been displaced meaning 50,000 ppm of something else is dancing with you in the room.  Therefore, when your Oxygen sensor alarms at 19.5%, there’s approximately 75,000 ppm of something else in the air you are metering and breathing without your mask on. Once again this could be a toxic, flammable, or hypoxic atmosphere that you have willingly invited into you’re body. As one of our instructors Ben Bosley says “how many chemicals do you want in your body that you didn’t want there”.

Many times, I have heard responders say,

“My Oxygen dropped but the other sensors showed nothing.  The Oxygen sensor must be bad.”

The other sensors don’t see everything.  Thus, your Oxygen sensor can tell you that something else is in the air, and that you should take action to protect yourself. The results of these situations are that you were lucky that day it wasn’t a toxic, flammable, or hypoxic atmosphere.

Or you were not lucky and your body will tell you this a few years later when it rears its head as cancer or some other major medical issue etc.!

An Oxygen reading of 23.5% means the air is Oxygen enriched.  This means increased flammability risk in this environment.  Thus, protective action should be taken immediately, especially TOG and SCBA.

The average lifespan of an Oxygen sensor is approximately 2 years (some say 3-5 now a days) from the time it’s opened and exposed to air.  The chemical reaction that measures the Oxygen continues 24/7.  Thus, even if the meter is seldom used the Oxygen sensor will degrade over time and fail. The O2 sensor is literally a non-rechargeable battery, and degrades over time.

LEL Sensor

The Lower Explosive Limit (LEL) sensor is another sensor commonly misunderstood.  News reports of gas explosions and injuries to first responders are all too common.  Properly used, the LEL sensor will reduce the risk to you and your crew from flammable atmospheres.  Most First Responders LEL sensors are a catalytic bead technology which we will focus on in this article.

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There are now numerous LEL sensors on the market that function differently and have limitations for the Fire Service.  Its critical you know which sensor you have and its limitations to you on a response. In other words, is the LEL sensor you have right for the mission you’re performing.

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The catalytic bead is heated to a set temperature; exposure to traces of flammable gas will cause the bead to react (oxidize), which is measured and interpreted into the LEL reading.  For this article, we will focus on the flammable gas Methane (Natural Gas) and a meter calibrated to Methane.

Methane has a flammable range of 5% - 15% in normal air.  This equates to a flammable range of 50,000 ppm for LEL and 150,000 ppm for the Upper Explosive Limit (UEL).  Our focus is the LEL, the minimum concentration at which explosions can occur.  If we detect the UEL in an area, that means we already passed through the LEL and flammable range, we never want to be in this situation!  We seek to detect the gas long before we get to the LEL and mitigate the incident in the safest atmosphere possible.

The LEL sensor reads from 0% to 100%, in 1% increments.  It is reading a percentage of the LEL.  5% Methane = 50,000 ppm.  So a LEL reading of 1% on your meter means it is reading 500 ppm at that spot.  LEL sensors on most meters are set for a Low Alarm of 10% of the LEL (5,000 ppm). Realize that your meter is only sampling approximately a fist full size of air at any given time.

You are reading %LEL not %Volume, these are two distinct differences that many firefighters do not understand! Many gas companies meter in % volume, we meter in % LEL.

OSHA designates 10% of the LEL as an IDLH atmosphere

(Not 10% volume, but 10% LEL)

You should be in full PPE at this point.  The High Alarm is usually set at 20% of the LEL (10,000 ppm).  Alarm settings may vary per local SOPs.  As you move into greater levels of gas the reading will climb.  As it approaches 100% of the LEL, the sensor will shut itself off, to prevent it from becoming an ignition source even though they say they are intrinsically safe.  The meter will usually display “OR” for overrange for some models.

100% LEL display reading will vary between manufacturers.

Do you know what you meter reads when it reaches 100% LEL? 99% of the fire service does not know the answer to this question. That is just unacceptable in my opinion! Another reason why The Meter Guys exists!

Once it reads “OR” and shuts down, it will NOT start up again until you follow the manufacturers procedures. Never restart your meter in a flammable atmosphere!

“I can smell gas, but I have no readings.” 

From 1 to 499 ppm, your meter will read 0% LEL even though Methane is present. The additive Mercaptan is what you are smelling not the Methane.  It can be detected as low as 1-2 parts per billion by your nose. Your LEL sensor will not register 1% till 500 ppm are present.

How do we track down a small leak from an appliance below 1% LEL?  Many departments utilize a metal oxide combustible gas detector (MOX), commonly referred to as a gas sniffer in the fire service.  It detects natural gas down to approx. 20 ppm, and is intrinsically safe, or is it? You better read your manual on this one! The MOX usually comes with a flexible probe to get into small tight spaces.  It only detects gas, it does not measure LEL accurately over certain levels, think of it as a Geiger counter to find gas leaks.

FYI did you know some shipments of Propane are non-odorized! Never trust your nose

Metering Pitfalls

Methane is lighter than air.  It will rise inside a building and can be trapped above drop ceilings and in other enclosed spaces.   Propane is heavier than air, and in a structure will gather at floor level or work its way down stairwells and vents to lower elevations, especially sumps and sewers.  When entering a structure, you should meter from the floor to ceiling.  If the air is still, you can have dangerous levels of gas above or below, while getting no readings at face level.

Some meters read slower than others, and even slower when cold.  It can take up to 30 seconds to get a reading (this does not mean it’s an accurate reading it just saw something and is responding) in certain conditions. Metering is a slow deliberate process, something we are not geared toward.  Take your time!  If you walk thru the door too aggressively, the meter could be in alarm for where you were 20 seconds ago.  Consider that if you read 1% of the LEL at the door frame, it is likely there are higher concentrations inside.  There is a thing called T90 it is the time it takes to get a 90% accurate reading.  What does this mean for you well LEL T90 times can range from 90-120 seconds and greater on some other sensors!

So, here is the reason we must meter slowly and methodically not like a coyote trying to get back to bed in the middle of the night. You all know what I mean!

Here is a simple way to help with this issue and change the way we do business.  Upon entry give the meter 30 seconds to respond, if it doesn’t proceed farther in and repeat this process. If it does respond give it another minute to get a more accurate reading.  Then there is the person that says, “how do I know when 30 seconds is up”.  Well, there is this thing called a PASS device that begins to alarm at 30 seconds. Yup another reason to wear your SCBA on a call.

Underground leaks can pose a different hazard.  Mercaptan can be scrubbed from the gas as it seeps through the ground.  I had a responder tell me they had this happen on a call with snowpack filtering the Mercaptan as well. Do not be led astray because you can’t smell the mercaptan it could cost you and your crew dearly!

If your meter says there is something there believe it! To trust your nose over the meter is a recipe for disaster. I have read many LODD’s and Near Misses that state this exact thing happening!

Complacency is an insidious risk to firefighters especially at a gas leak and can have catastrophic consequences.  There is more to cover with metering skills.  This article is just a taste.  Become proficient with your meter.  The 4-Gas meter should be part of your response just as your Irons and TIC. Train yourself, train your crews, to be as safe as possible.

The Meter Guys exist to overcome the short comings in the Fire Services metering culture. So many people think metering is a Hazmat Tech skill only, I will disagree with the statement to my grave! The First Responder is the first in and should be prepared to use their meter proficiently, this is what The Meter Guys bring to the table.  The Meter Guys have been on this issue way before NFPA 1010 even addressed it. You want to get your personnel the best meter class they will ever take reach out to The Meter Guys you won’t be disappointed! This is what we do.

Words of wisdom! If you’re ever on a call and someone says I can tell how much gas is in here by the smell. Do me a favor get the hell out that person has no idea what they are talking about!

Finally,

"Don’t live to build your kids a treehouse

Live to build your Grandkids a treehouse!"

Scott Russell

Owner of The Meter Guys