What Your Meter Isn’t Telling You – And Why That Matters

I sat down again with Bobby Salvesen and Mike Monaco, the voices behind The Haz Mat Guys, and what started as a joke about tongue-twisting episode titles quickly turned into one of the most practical conversations we’ve had yet. Episode 71 was all about meter readings, sensor responses, and how misunderstood a little blinking screen can be if you’re not careful.

Turns out, your meter might be telling you everything you need to know – or absolutely nothing at all – and the difference is usually in how you interpret it.

Reading Numbers Is Easy. Making Them Make Sense? That’s the Job.

We kicked things off with a reminder that every meter is speaking a language, and it’s on us to become fluent – and to translate that language for the rest of the team. Bobby said it best when he joked, “I can understand it, but making others understand it? That’s a whole other game.”

For example, “2 parts per million” (PPM) sounds technical, but without context, it’s meaningless. If the danger threshold is 1 PPM, then 2 PPM should light a fire under everyone on scene. If not, it’s just noise.

This disconnect is especially dangerous when explaining risks to decision-makers like chiefs or commanders who may not be trained in hazmat operations. If they don’t understand what you’re saying, they’ll either do nothing – or worse, do something totally wrong.

LEL, PPM, and the Art of Talking Like a Human

The conversation really got interesting when we dug into how readings like the Lower Explosive Limit (LEL) and percent by volume are often miscommunicated.

Here’s a real-world issue: power companies in New York read gas levels as “percent by volume,” while hazmat teams read them in percentage of the LEL. So a reading of “2.5%” on one meter could mean “50% LEL” on another, but unless both sides know what the other means, it’s a dangerous game of telephone.

Mike compared this confusion to telling someone they have “280,000 parts per million of oxygen.” Technically correct. Practically useless.

So what’s the fix? Pick one unit system and stick to it. Standardize your language across agencies and teams, and when that’s not possible, explain the conversion in simple terms.

Qualitative Meters: The Hot and Cold Game

Not all meters spit out numbers. Some just buzz louder the closer you get to a leak. These qualitative sensors, like metal oxide detectors, work like a game of “hot and cold” – they’re incredibly useful for locating sources but useless for quantifying risk.

Knowing when to use which type of meter is crucial. If you’re looking for a leak, you want a high-resolution, qualitative meter. If you’re trying to understand exposure risk, you need hard data from quantitative sensors.

Know Your Meter’s Limits – Literally

A big chunk of our talk circled around the concept of response range and resolution. In plain terms:

• Response range is how much your meter can “see.”

• Resolution is how small of a change it can detect.

For instance, a CO meter that tops out at 500 PPM won’t tell you if you’re at 501 or 5,000 – it just says, “I’m done.” That’s a problem, especially in volunteer departments where basic, single-gas meters are the norm due to budget constraints.

As Bobby warned, “If you’re seeing oxygen displacement, you’re probably already on your back.”

Some sensors also rely on oxygen to function. Catalytic bead sensors, for instance, won’t work in oxygen-deficient environments. Others like infrared sensors will still operate. If you don’t know what kind of sensor you have – or how it behaves under stress – you’re playing roulette.

Latching vs. Locking Alarms: Know the Difference or Get Burned

Here’s a term I didn’t fully appreciate before this episode: locking alarm. While most meters have low and high alarms, some have a third layer that essentially says, “I’ve seen too much. I’m not talking until I reboot.”

Locking alarms happen when the sensor is overwhelmed – usually to protect it from damage. Unlike a latching alarm, which resets when you leave the danger zone, a locking alarm requires a full meter restart.

Not knowing the difference can lead you to think the air is “safe” just because the meter went quiet. It’s not. It’s just done trying.

Mike had a perfect analogy: “It’s like my kid latching to my chest before realizing I’m not my wife.” Once the meter latches (or locks), it’s reacting to the environment – and it won’t let go until it’s safe.

Radiation Meters: Bigger Isn’t Always Better, But It Usually Is

When it comes to gamma and neutron detectors, size actually does matter. Bigger detectors have better resolution and can detect smaller changes in background radiation. But once things heat up, you may need to switch to a different meter entirely. If you max out a 25 millirem/hour device, you won’t know if you’re at 30 or 300 – either way, you’re blind.

Radiation alarms are always latching. That means once you leave the hot zone, the alarm will reset – unless you’ve received a dose, not just a dose rate. Big difference.

Training Isn’t Optional. It’s the Job.

Bobby and Mike both hammered home one key takeaway: knowing how your meter works isn’t a luxury – it’s the baseline.

That includes:

• Knowing which gases read in PPM and which in percent

• Understanding that “normal” readings vary by environment

• Recognizing when a meter is maxed out and no longer reliable

• Identifying when environmental factors like heat or humidity can mess with your gear

Hazmat techs aren’t just meter operators. They’re interpreters, translating complicated signals into plain language that can guide life-and-death decisions.

Final Thoughts: Don’t Just Read the Numbers – Understand Them

This episode reminded me how often we take our tools for granted. A meter doesn’t save lives. The operator using it properly does. And proper use means knowing what your meter is telling you and what it’s not.

Whether you’re walking into a house with a CO call or running a large-scale industrial incident, your readings are only useful if you understand their context, limits, and implications. That’s the true skill of hazmat response.

Let’s hear from you: What’s your go-to analogy for explaining meter readings to a chief or new team member? Ever had a meter go silent when you needed it most? Drop a comment below or shoot us a note – we’d love to include your stories in a future episode.