New hydrogen sensors available

20 August 2020
Hydrogen – the underestimated danger

Lead-based batteries are charged by means of a chemical process that emits hydrogen gas as a byproduct. Depending on the design of the battery, this hydrogen escapes from vent valves or is released directly into the environment. This is hardly the case with AGM batteries, but it occurs to a significant extent with "wet cells". Hydrogen is odorless, colorless and lighter than air - in smaller concentrations it is nothing unusual in nature and does not constitute any risk.

It is a different matter in battery rooms:

 If no safety measures or only insufficient safety measures have been taken, the hydrogen can no longer escape. The percentage of hydrogen that must be released into the environment inevitably increases with the number of batteries. Hydrogen is lighter than normal air, so it rises and collects in the form of "bubbles" in poorly ventilated locations that can be found everywhere within a room: 

  • In ceiling areas or in dropped ceilings

  • Storage areas such as shelves

  • Static air vortices in the ceiling area due to ventilation

As soon as a general air saturation of at least 4.1% hydrogen to 75% air is reached, a highly explosive gas mixture is formed. Even small sparks from switched or electrical discharges can be enough to ignite it. 

Hydrogen saturation in the air is colorless and odorless so special sensors are required in order to be able to counteract the formation of such a gas mixture. A battery monitoring system shows the battery parameters and would also detect loss of liquid due to gas formation, but only far too late. It is therefore recommended to use a hydrogen sensor as an additional safeguard for larger-scale systems in poorly ventilated areas.

 With the SM_H2, GENEREX has had a special-purpose gas sensor in its product range for precisely this problem since 2017.

This UL-certified sensor is available on the European as well as the American market and offers professional additional protection with up to 3 sensors that can be placed anywhere. The cable length of up to 7.5 m between the base station and the sensors also enables very wide-area monitoring.

Some highlights the SM_H2 includes:

An autonomous all-in-one solution in the event of an emergency

 If there is an emergency in which the entire IT infrastructure has collapsed, the SM_H2 can independently continue to monitor the environment as a standalone device and has its own acoustic and visual warning system for indicating hazards on site. The basis station also has the ability to connect to two different voltage sources, which allows for the use of an independent emergency power supply system.

Rapid limitation of risk in the event of a failure

Both the connected probes as well as the base station have LED signals on the cable connection ports so that the location can be quickly and easily identified in the case of wide-area monitoring.

Potential-free contacts

Potential-free contacts that can be used to connect to relay stations or higher-level management systems are available for both the warning as well as the alarm.

New for the European market starting 2020*:

 With the SM_H2_LC, GENEREX is introducing another high-performance hydrogen sensor on the European market that is not UL-certified but has an impressively lower price because of this.  The highlights of the inexpensive SMH2LC include:

Easy installation and centralized configuration

The sensor heads are pre-configured and calibrated –No additional configuration work on the sensor station is required. Like his “big brother”, the sensor provides a warning and an alarm level.

Power supply from the base station

As the central control unit, the BACS Webmanager with the GXRAUX module also handles the power supply. Up to 15-meter-long cables can lie between the Webmanager and the sensor for structured cabling.

Daisy chains and visual warning behavior

Up to 5 sensors can be coupled in a daisy chain. While the Webmanager is indicating an error, the cause of the warning or alarm can be identified through a simple on-site visual check.


In addition to hydrogen, the standard sensor also responds to other gas accumulations such as nitrogen. The internal sensor technology can be easily exchanged as needed and thereby adapted to the respective operating environment with its particular gas mixtures.


In general, all gas sensors on the market must be calibrated at regular intervals. A special feature of the SMH2LC is that this calibration is especially easy to carry out: The user unscrews the sensor and mails it in, then a new sensor is promptly sent back while the sensor that was sent in is calibrated and stands ready for the next exchange. The uncomplicated exchange of the sensor by the user also makes the calibration significantly less expensive than with other H2 sensors on the market.

The new SMH2LC will be available for order in the GENEREX portfolio starting April 2020.

 *) The sensor is not UL-certified and is therefore not permitted to be used on the American market