You see them and drive past them all the time. Every community has one. Chances are that a close neighbor, one of your best friends, or even a member of your family may work in one. When low pressure sets in, and the wind blows in the right direction, the stench is horrific. But the smell is only a hint to the abundant hazards that you might encounter when working at a wastewater treatment plant.

gas hazards at wastewater treatment plnts

Employees and contractors at wastewater plants need to take extra caution when working around open pits.

The potential for slips, trips, and falls exists in wastewater treatment plants and those basic hazards become more acute when dangerous gases in the air throughout such a facility precipitate them. The possibility of severe trauma or even drowning from falling into a confined space, such as a wet well, recirculation pit, or a clarifier tank, means the risk associated with working in a wastewater treatment plant may by higher than we recognize or care to admit.

The main gases of concern in wastewater treatment plants are methane, hydrogen sulfide, and oxygen (or the lack thereof). Hydrogen sulfide and methane are the byproducts of the decomposition of organic materials that exist in the waste flows feeding the plant. The buildup of these gases may lead to the lack of oxygen, or in some cases, explosion, when coupled with a source of ignition.

But the number of gas hazards present may be too numerous to name. Beyond the big three gas hazards are the dangers that exist from purifying chemicals such as ammonia, chlorine, chlorine dioxide or ozone that are used in the decontamination of the waste and effluent water. Potential for an unlimited number of toxic or explosive gases exists from the chemicals that may be spilled or dumped into the waste system from the industrial base in the community.

Elimination of these gas hazards is virtually impossible, so permanent workers and contractors must depend on reliable gas detection equipment to protect them. Although there is not one “silver bullet” gas monitor that will protect every worker in every situation, a basic multi-gas monitor is a good place to start. A standard four-gas monitor equipped with the proper sensors provides protection from the primary methane, hydrogen sulfide, and oxygen hazards. The fourth gas sensor, usually carbon monoxide, can often be replaced with an ammonia or chlorine sensor to add protection against one of the more prevalent chemical hazards. Upgrading from a four-gas to a five, or even six-gas monitor, may allow you to advance the level of detection and protect yourself from even more of the potential chemical hazards.

Unfortunately, protecting workers from the dangers of gas hazards is not as easy as simply handing them a gas detector and sending them out the door. If workers do not use their monitors properly, do not understand how their monitors work, or do not know how to react to the readings, gas detection devices will not be very effective.

First, the monitor must be turned on. Workers must know how to turn the monitor on and verify that the instrument they are carrying is capable of detecting all of the hazards that they may encounter. Next, if workers want to ensure they are protected, they must ensure that the monitor will actually detect the gases it is supposed to detect. This is accomplished by performing a bump test of the monitor by exposing it to a concentration of each gas it is designed to detect and verifying that the sensor responds and the instrument alarms properly. The simple truth is that the only way to be certain that a gas detector will actually detect the gases that it is supposed to detect is to test it with gas. It may sound like a complicated procedure, but it is as simple as placing the monitor on a test stand or docking station equipped with the appropriate gases and having the test run automatically. This should be done each and every time the monitor is used.

The more hazards that a monitor is intended to protect against, the more understanding there must be of how the sensors in the monitor interact. For instance, a user with a monitor having both hydrogen sulfide and chlorine sensors installed must understand that the presence of H2S in the atmosphere may negatively affect the reading from the chlorine sensor and mask the presence of a dangerous level of chlorine gas in the atmosphere. Users should refer to the instrument manufacturers for information on the cross interference levels and interactions between sensors.

Gas detector alarm action messages

Alarm action messages provide helpful instructions to the user based on the gas level.

As much as understanding the sensors themselves, the worker has to understand what the proper response is when the monitor does detect gas and go into alarm. Often, when a gas detector alarms, an untrained user may panic and do something that creates a further danger, or they may simply ignore the situation because they do not know what to do next. Some new monitors today provide alarm action messages that display text instructions guiding workers toward the appropriate actions when the monitor alarms. Telling workers to “WEAR A RESPIRATOR” or “EVACUATE” when their instruments alarms will reinforce the hazard training he had previously.

Realistically speaking, there may be instances when the monitor is simply not capable of providing the necessary protection quickly enough and a worker may be overcome by a gas hazard or incapacitated in some other way. It is important that the monitor a worker carries has the means to let others know that the worker is in danger. Instruments may be equipped with a panic button that lets the worker signal others when he is in need of help or a motion detecting or “man down” alarm that sounds when a worker is motionless. More advanced instruments may have the capability of triggering alarms on other workers’ instruments when one worker’s instrument goes into alarm. These features may all be key to finding and rescuing a victim of exposure before it’s too late.

Gas hazards are an unseen and unavoidable fact in the operations of a wastewater treatment plant. If you are contracted to work at or very near to one of these facilities, having the right gas detection equipment and using it properly is the best way to ensure that you return home safely at the end of the workday, even when the wind blows in the right direction.


area monitor for confined space




This article was featured in the June 2016 edition of Construction Business Owner Magazine.