Home Podcasts THMG016 – Metering Techniques and Reading the Numbers

THMG016 – Metering Techniques and Reading the Numbers


Toxicity testers like this one are used by Urban Search and Rescue teams' hazardous materials specialists to see if there are any dangerous chemicals in the area they’re about to enter

In this episode, Bob and Mike continue on the metering trail with installment #3. We cover how techs actually take a reading, when your meter will display a number, and what to do when you don’t have a number.

Complete Show Notes

3:00 How We Use Meters and What They Show Us

  • Meters don’t tell us everything, but they can tell us if some gasses are present – allow you to eliminate some hazards and threats
  • Interpretation is key to determining if an atmosphere is safe
  • Monitoring considerations
    • Scene assessment
    • Meter selections
    • Monitoring with different types of meters
    • Battery checks
    • Starting up and fresh air setup
    • Establish a background
    • Interpret data
    • Radio the results

8:30 Metering Priorities

  • If you understand the basic foundation of hazards, this order is common sense
  • 1. Radioactivity
  • 2. Flammability
  • 3. Oxygen
  • 4. Toxicity
  • 5. Corrosives
  • 6. Other chemicals

10:20 Metering Methods

HazSim Product

  • Entry team carries primary meters – they’re chosen based on initial entry and information
  • If people are sick, you’ll use a WMD, single gasses are used in commercial or industrial settings, and halocarbon meters for freon
  • You might also do a second sweep with a secondary meter – for example, you might use a FID if you don’t pick anything up on a PID
  • If you’re sampling a liquid, one person should handle the product and another should handle them once they’re in test jars – then, the sample is brought to a warm zone and tested

13:20 Metering with pH Paper

  • Toss and read method
    • Throw pH paper into liquid and read it without removing it
    • This is the least professional method
    • Identifying your strip can be difficult when a bunch of them build up
  • Pipette/dropper technique
    • Sample is removed and placed on a strip
    • Professional method that’s also clean
    • Allows you to run multiple tests while staying in control
    • However, it isn’t an efficient method for titrations and requires extra equipment and time
  • Dip method
    • While holding the strip, dip it into the product and pull it out
    • This looks professional, is fast, and requires no other equipment
    • However, it requires close contact with your fingers and might involve a lot of bending
  • Tape to a stick
    • Dip pH paper after attaching it to the end of a stick
    • Professional method that allows sampling without bending down
    • Great for awkward or hard to reach areas and keeps your fingers and body away from the product
    • Also gives you full control of strip and product, but the longer the stick, the less control you have
    • Keep in mind that the metal might react with whatever you’re dipping the paper with
    • Used for atmospheric monitoring
    • Good for initial entry
  • Tape to facepiece
    • Good for atmospheric monitoring – one wet and one dry
    • Wet paper picks up vapors faster – if both turn at the same time, you have a lot of that substance in the air
    • Allows you to continuously monitor the air because you can see it turn
    • Tape it to your arm or body – requires you or your partner to remember to look
    • No real cons other than taking up room on your facepiece

19:30 Thermal Imaging Camera

  • In hazmat, this is used to look for anything out of the ordinary from a thermal point of view
  • Chemical reactions produce a change in temperature – exothermic and endothermic reactions are possible
  • Don’t confuse these changes with physical changes in matter – we’re concerned with chemical changes
  • Camera must be used to monitor over a period of time, so it’s important to constantly watch to see if there are any changes
  • Reactions take time to heat up – when reactions speed up, we get more heat and more reaction
  • Remember that you’re only getting data, which is a piece of the bigger puzzle

23:05 Leak Detection

  • There are meters that allow us to rapidly reduce our search time for finding leaks
  • Most of them work off of sound – the higher the pitch/faster the tone, you know you’ve entered a greater concentration
  • Most require you to start in fresh air to reduce the tone to its lowest audible sound/pulse
  • Recalibrate the meter as you approach the source to make it less sensitive – this lowers the tone or pulse

25:45 Intrinsic Safety

  • This is a method of engineering electrical devices – prevents the device from being a source of ignition
  • Why meters ignite
    • Electrical – sparking, arcing of current
    • Thermal – heat from device, light bulbs in flash lights
    • Mechanical – heat, sparks, metal rubbing together
  • Reduces energy transfer by sealing off electrical circuits using vapor tight gaskets
  • Insulation or heat sinks may help keep high temperatures from coming in contact with material
  • Many intrinsically safe devices require tools to access the battery

28:45 Meter Ratings

  • Ratings are based upon the types of materials it can come into contact with
  • ANSI (American National Standards Institute), NFPA (National Fire Protection Agency), and NEC (National Electrical Code) all play a role in helping to define the various codes that flashlights fall under
  • Substances are divided up into classes
    • Class I – area where flammable vapors and gasses are found or may be present
    • Class II – deals with and protects against combustible dust
    • Class III – easily ignitable fibers and things larger than dust
  • Also divided into groups based upon the rating for specific flammable gasses
    • Group A – acetylene
    • Group B – hydrogen, butadiene, ethylene oxide, propylene oxide
    • Group C – ethylene, cyclopropane, ethyl ether
    • Group D – propane, acetone, ammonia, benzene, butane, ethanol, gasoline, methanol, natural gas
  • All of these gasses are grouped by similar flammability characteristics and fire behavior
  • T-Code – this is a temperature standard where each code represents the temperature a device will get to
  • T1 is the highest temperature of 450 degrees Celsius, while T6 is the lowest at 85 degrees Celsius
  • It’s important to remember that we’re not intrinsically safe, and our tools aren’t either
  • Don’t let intrinsic safety become a top priority unless you know you’re going into a flammable atmosphere

35:50 Limiting Hazards for Intrinsic Safety

  • Measure the LEL and change the atmosphere until you can use your meter safely
  • Decomposition and sewer gasses are two reasons why oxygen may not be present
  • Oxidation and rust are also relevant because oxygen is responsible for rusting
  • Combustion also consumes oxygen
  • Adsorption – concentration and depth
  • Generally, the deeper we go, the worse the oxygen – heavier than air gasses accumulate

38:30 Erroneous Readings

  • Meters can be negatively affected by temperature, humidity, smoke, corrosives, dirt, oxygen-deficient atmospheres, oxygen-rich atmospheres, and combustible airborne mists/dusts
  • The volatility of a substance is also important and refers to how readily a substance gives off vapors
  • A vacuum, increased temperature, or increased surface area can all increase volatility – high vapor pressure generally means high volatility
  • Low volatility may mean there are fewer vapors in the air and less of a chance that those vapors will reach flammable limits – the lower a substance vapor pressure, the more persistent it is

39:55 How Do We Read an Atmosphere?

  • Assume you’re dealing with an unknown substance, even if you’re told what the substance is – never trust the information you receive until your team verifies it
  • Check your meter in fresh air and use that as a baseline
  • Take your reading at the door and then go through the same procedures you would anywhere else
  • Sample at the ground (most vapors are heavier than air), waist high (this is the area where we are), and overhead (only a few gasses rise)
  • Remember that all other possibilities must be eliminated before you come to a conclusion
  • Read at each height before stepping forward and remember your hose time to read
  • Pumps on meters are around one second per foot (give or take) – we don’t move at one second per foot in our search
  • Confined space wands and hoses can take a few minutes to respond
  • Don’t immerse your probe in liquid
  • Remember that some chemicals may damage the sensors – saturated sensors can be put in fresh air and ran until they’re cleared

46:40 Metering and Decon