Hydrogen Sensor: A Safety Hydrogen Detection Instrument

Hydrogen sensor is a vital industrial gas that might also play a significant role as a clean, carbon-free fuel. However, hydrogen has one problem. It is highly flammable. And since the gas is odorless, tasteless, and colorless, you can only rely on detectors to check the presence of hydrogen. Hydrogen sensors are the primary components in these detectors, and we will analyze them in detail to explain how they function. Take a look!

What Is a Hydrogen Gas Detector?

A hydrogen gas detector is an instrument used to measure hydrogen concentrations in air. Also known as a hydrogen sniffer, monitor, analyzer, or tester, the device contains the following:

• A long-lasting battery
• Hydrogen gas sensor
• Display to show the detected hydrogen gas concentration
• LED
• Buzzer and vibration alarms
• Belt clip for hooking to clothing

The display shows the concentration of hydrogen in parts per million (ppm), and most units can detect low levels of between 0-1000 ppm. But others measure higher concentration levels in %LEL (Lower Explosive Limit).

How a Hydrogen Gas Detector Works

A hydrogen sensor is the core component of the device, and it works with the inbuilt electronics to convert the detected hydrogen into an electronic signal. An onboard microprocessor analyzes this signal, then provides the output on the built-in display. If the hydrogen levels exceed the preset value, the device will activate the alarm to warn the user.

Types of Hydrogen Sensors

There are three primary hydrogen gas sensor types.

Pellistor Sensors

Also known as catalytic-bead sensors, pellistor sensors use catalysts to cause flammable gas inside to ignite at lower-than-usual temperatures. This oxidation changes the element's conductivity, which alters its resistance. The change in resistance is proportional to the hydrogen gas concentration.

This device then derives the quantity of hydrogen from this measurement and expresses it as %LEL. Since 4% hydrogen gas concentration is explosive, it corresponds accurately to 100% LEL. So these detectors are some of the most reliable, robust, and cost-effective types.

An LEL gas detector

But there's one problem. These sensors detect all flammable gasses, making them catch-all technologies for combustible gas detection.

Pros

• Affordable
• Simple and reliable
• Ideal for %LEL range
• Five to ten-year lifespan

Cons

• Requires power for heating
• Needs startup time for heating (slows sensor response)
• Non-selective (detects any flammable gas)

Electrochemical Sensors

This sensor reacts hydrogen with an electrolyte or electrode to trigger an electrochemical reaction. The current generated from this reaction is proportional to the amount of hydrogen in the air.

This design creates a more sensitive hydrogen gas level detection than the Pellistor type. And these sensors offer varying sensitivity ranges that can go from 1-1000 ppm to 0-40,000 ppm.

But there is a downside. This extreme sensitivity makes the sensors susceptible to damage when exposed to high gas levels that exceed their measurement range. So these sensors are suitable for hydrogen detection where low levels are critical.

Pros

• Tiny
• Cheap
• Quick response time
• Zero startup time (turns on immediately)
• Easy to integrate with electronics

Cons

• A short lifespan (2-3 years)
• Carbon monoxide sensitive

Semiconductor Metal Oxide Sensors

These film sensors contain a metal-oxide material sensing film that interacts with hydrogen molecules to create a redox reaction. A power-law relationship then occurs between the sensor conductivity and gas concentration.

But the sensors can react and respond to other vapors and gases, meaning there is a high likelihood of false alarms.

Pros

• Over 5-year lifespan
• Ideal for the ppm range
• Low cost
• Robust

Cons

• Requires a warm-up time (about 5 minutes)
• Non-selective
• Influenced by humidity and temperature

Types of Hydrogen Gas Detectors

There are three primary hydrogen gas detector types.

Detector for Personal Protection

Most hydrogen gas detectors are portable, battery-powered units that you can clip to your clothes. These devices provide continuous personal protection using buzzers, LEDs, and vibration alarms. They usually come in the following varieties.

A portable gas detector

• 0-1000 ppm (Low level): These devices can sniff low gas levels and serve as early warning systems to protect you from exposure to hydrogen. Most of them use electrochemical sensors.
• 0-100%LEL (EX LEL): As the name suggests, these detectors display results in the LEL range. So they feature combustible pellistors or catalytic bead sensors.

Hydrogen Leak Detector

Gas leak detectors are combustible analyzers that use semiconductor sensors to sense tiny hydrogen concentrations in the ppm range.

But some have the combustible pellistor (catalytic bead) sensor because the EX 0-100% LEL is ideal for detecting 100% gas leaks. The other sensor types can get damaged when pinpointing the location of hydrogen gas leaks because the concentration might exceed their ppm measurement range.

A gas detector to check explosive, flammable, and toxic gasses

So the EX LEL analyzer is the best for such applications, usually in industrial processes.

Hydrogen Gas Monitor for Fixed Wall

These fixed-wall units provide continuous hydrogen protection, a vital sensor response safety feature indoors, such as in power generation or battery rooms. The units sound alarms and can trigger vent systems to turn on once the hydrogen levels rise above the preset threshold.

What Are the Safe Hydrogen Gas Levels

Hydrogen is non-toxic to human beings. The safety hazards concerned with exposure to hydrogen are due to its flammability as a gas, not its toxicity. So there are no recommendations on safe hydrogen gas levels provided by governmental bodies like NIOSH, ACGIH, and OSHA.

But the EPA recommends personnel evacuation if the hydrogen gas levels reach 10% of LEL. The explosive limit for hydrogen is 4.1% (4,100 ppm), so 10% of this value is 410 ppm.

Applications of a Hydrogen Gas Detector

Hydrogen sensors have several uses, such as the following.

Ammonia Synthesis

The majority of the hydrogen produced globally goes into ammonia production. The process involves reacting atmospheric nitrogen with hydrogen to make the compound. Ammonia is a primary component in nitrogen-based fertilizers, and the ammonia synthesis process requires hydrogen detectors to measure the gas levels.

A petrochemical plant for ammonia synthesis

Oil Refineries

The hydrogen economy is growing and will play a primary role in global energy supply decarbonization. But hydrogen still plays a critical role in refining fossil fuels, specifically in the hydrocracking process. Hydrocracking involves reducing heavy gas oils to constituents with a lower molecular weight.

A mega installation for hydrocracking in an oil refinery

The equipment used for this process is complex, meaning there are higher chances of leaks in confined spaces. These hydrogen leaks can cause accumulation to dangerous levels and asphyxiation. So, such applications require handheld and wall-mounted hydrogen detectors for warning purposes.

Battery Rooms

Energy storage in batteries is becoming more typical in homes and industries, especially with the rise in renewable energy. Lead-acid batteries are some of the most used storage options because they have a high energy density. But they produce hydrogen when recharging, which can accumulate to high levels in poorly ventilated rooms. So continuous monitoring is essential to minimize fire hazards and ensure personnel safety.

A battery room

What Is a Bump Test?

Bump testing involves exposing the detector to a tiny amount of the target gas (hydrogen) to ensure it operates and activates alarms as required. We recommend doing bump tests to sensors when new, then repeating the tests weekly. But if using them in life-threatening areas, do the tests daily.

Do Hydrogen Gas Detectors Require Calibration?

These sensors can degrade and drift over time. So we recommend calibrating them every 6-12 months to ensure they maintain accuracy. The calibration process requires specific equipment, such as gas regulators, calibration gas bottles, calibration cap fitting, and tubing.

A technician calibrating a gas detector

You should confirm the calibration gas mixture and concentration from the manufacturer. But we recommend calibration at 100 ppm for forensic hydrogen gas detectors.

Wrap Up

In conclusion, hydrogen sensors play a vital safety role in industrial applications and will be critical in the hydrogen economy. But they are available in multiple types with varying sensing responses that suit different applications. So you need to understand how each type works to pick the best one for your project. We hope this article clarifies these details for you. But don't hesitate to contact us if you need further assistance.