Gas Monitors

With the recent manure gas incident in Wisconsin, there has been increased interest in safety around manure handling equipment.  Below is an informational article on gas monitors.

Provided by UW Extension Farm Safety Specialist Cheryl Skjolaas

Investing in a gas monitor – Which one should I buy?

Recent incidents with loss of life – human and cattle –demonstrated known and unknown factors of manure gases. Especially, dangers and deadliness of hydrogen sulfide were proven. Given unknown factors of where gases will be released, concentration of the gases and how gas plume will disperse; the only means to know what’s in the air that’s sustaining life is to monitor for gases.

There are several types of air sampling instruments available. For ease of use and the conditions that you will be working in, a gas monitor (meter) would be a good investment.  There are two main categories of gas monitors – single gas and multi-gas. Here are a few questions to get you started on determining what type of gas monitor would work into your safety programs.

  1. Where will the gas monitor be used? Write down all the potential places you could use a gas monitor if you had one. Open air, non enclosed manure storage, transportation vehicles (truck or tractor operators—in the cab and when walking around equipment), confined space manure storage, cleaning out a tanker, manure handling system, repair work to trucks, tankers or machinery in a shop, grain or feed storage bins, upright or horizontal silos during high risk times of silo gasses
  2. What atmospheric conditions (gases or dusts) are you concerned about in each of the situation that you identified in question 1.
  3. Which of question 1 situations, require a confined space entry? Or is it a space that you need to test the atmosphere before entering. In these situations you want an internal or external pump, tubing and probe.  It’s probably more cost effective to invest in a gas monitor with an internal pump and accessories at time of purchase. If budget doesn’t allow that accessory at initial purchase, see if an external pump and accessories are available for the monitor.  Yes, you can drop a monitor down into a space on a rope, but it’s difficult to read the display and reading will change as you draw the monitor up.
  4. Will the person using the monitor be working alone? For example, agitation pump operator goes out to start agitation before rest of crew arrives or spends most of the work day in agitation zone.  In this situation, a motion alarm would be a feature to consider.

Single gas monitors – These may also be referred to as personal monitors or disposable monitors. For open air, non-enclosed manure storage and transportation of manure, hydrogen sulfide (H2S) is going to be the gas of concern.  In these situations, a single gas H2S monitor can be used. Most detect up to 100 ppm and then alarm that gas is over limit (OL) for the device. Remember 100 ppm is Immediately Dangerous to Life and Health (IDLH), you need to be getting out of that area right now or be on a supplied air respirator.  Single gas monitors are considered “personal monitors” as they should be worn by the person in their breathable space. In other words, worn on a shirt collar and not on the back pants pocket. A disposable single gas monitor has a limited life battery and sensor – typically 2 years.

Multi-gas monitors – Let’s start with a standard multi-gas monitor configuration. A standard multi-gas monitor has sensors for oxygen level (O2), LEL % or flammable gas (in case of manure this is methane), carbon monoxide (CO) and hydrogen sulfide (H2S).  Since CO2 will displace O2, high CO2 would factor into a low O2 level. The alarm rates will be preset to industry standards for alarms- these are good alarm limits. You may get a feature that lets you set alarms but standard levels are okay.

Sensors for non-standard gases are referred to as “exotic sensors.”  In agriculture, examples are nitrogen dioxide (NO2) with silo gas or ammonia (NH3). The company that makes a monitor capable of measuring 5 or 6 gases is MSA and the model is Altair 5X. If you’re needing a monitor for silo gas situations or ammonia levels in barns; this would be a monitor to consider.

How long will it take for the sensors to read a gas? If up to 2 minutes, that’s a long time if the monitor is on you versus you’re using a sampling probe and haven’t entered the space.

If you have a situation that potential may have explosive dusts, such as grain bins or drying manure solids; discuss this factor. Is this monitor certified for dust environments or any cross-sensitivities to be concerned about.

Replacement costs of sensors vary so ask about these costs. What is the life expectancy of each of the sensors? Will warranty cover sensor replacement?   You may find that a lower cost base model has higher cost when you get to maintenance costs.

What accessories are needed? As discussed in question 3, a sampling pump, tubing and probe is recommended for any confined spaces or entry situations.  There are basic confined space kits available from safety supply companies packaged with accessories, test gas canisters, regulator and all packaged in a case ready to go.

Test gas canisters and regulators are used for calibrating the monitor.  Basically, a known gas is passed over the sensors to check that monitor is working correctly.  One option to explore is whether or not the safety supplier offers calibration services.

Datalogging features are beneficial if you need to review exposure levels or for worker safety plans.  This feature is common on monitors. How you access data and system requirements are what differs.

Power source maybe batteries or a charging unit.  Investigate how long a full charge is expected to last.  This is a key consideration if you’re going to be out for an 8-12 hour workday and depending on the monitor for the whole time.

Where to Purchase? The best recommendations is to find a local safety supplier. Even better if they can provide service or technical support.  If a sensor goes out and you need a replacement ASAP, what do they have in stock? You’re having problems with a bump test or calibration test, can you stop in for assistance? Discuss warranties and how they are handled. Good service and technical support is very beneficial.