Entering a Tank: Proceed With Caution

Get the right equipment and follow these procedures to safely inspect the inside of your truck’s vacuum tank.
Entering a Tank: Proceed With Caution
Ronnie and Jennifer Tamez are owners of First Call Septic Services in Battle Ground, Washington. Send your Truck Corner questions to editor@pumper.com.

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From time to time we need to enter a truck’s vacuum tank (or a septic tank) to clean and inspect it. That means we must understand working in “confined space” and necessary critical safety precautions before entering an unknown atmosphere. We’ve all heard the stories online and during safety meetings of workers going into tanks, passing out, and then others going in behind them and passing out too, eventually leading to multiple deaths. The danger is real.    

Many workplaces include areas considered as “confined spaces.” They are not necessarily designed for entry by workers, but entry is necessary sometimes for inspection, maintenance and repairs. A confined space also has limited or restricted means for entry or exit and is not designed for continuous occupancy. Confined spaces include, but are not limited to, tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, tunnels, equipment housings, ductwork, pipelines, etc. For the pumper, septic tanks and truck tanks should be approached as confined spaces with a great potential for danger.

The Occupational Safety and Health Administration, or OSHA, uses the term “permit-required confined space” (permit space) to describe a confined space that has one or more of the following characteristics:

  • Contains or has the potential to contain a hazardous atmosphere
  • Contains material that has the potential to engulf an entrant
  • Has walls that converge inward or floors that slope downward and taper into a smaller area, which could trap or asphyxiate an entrant
  • Contains any other recognized safety or health hazard, such as unguarded machinery, exposed live wires or heat stress


I am guilty of entering septic tanks without taking the appropriate measures. However, I am not a hypocrite. These instances were before my training at WOSSA (Washington On-Site Sewage Association). I had been working under the misconception that ventilating the tank for 15 minutes would “remove” the confined space criteria. Now, I don’t know where I got that in my mind. Maybe I read it somewhere, and over time I believed this was the rule.

One of the keys to confined space safety is knowing what type of air is in the environment. Is it safe to breathe and enter? You need to pick up an air monitor to answer these questions. My air monitor was purchased at an Airgas welding supply store. They can be rented for about $35 and cost about $1,500 to buy. My monitor is the BW Gas Quattro. It tests for oxygen content, carbon monoxide, hydrogen sulfide, and lower explosive level gases. It is not required but recommended to get an Escape Breathing Apparatus or EBA. Depending on the model it can provide you with five or 10 minutes of air. The EBA is required if you can’t ventilate the tank to safe levels.

Following this web address will take you to a video of me demonstrating air quality sampling inside a septic tank: youtu.be/SlLTCSkTt9Y. I have sampled the air from 1,000 septic tanks before entering. And 999 times the sample came back good, and no worries. Seldom is a problem encountered. But there is the one time, and the video proves that dangerous levels of gas are found inside a tank. I looked in this tank, like I do every time, and I didn’t see anything wrong. But I ran my sample before entering, and it showed 2,600 ppm of CO.

Carbon monoxide is harmful when breathed because it displaces oxygen in the blood and deprives the heart, brain and other vital organs of oxygen. Large amounts of CO can overcome you in minutes without warning — causing you to lose consciousness and suffocate. Besides tightness across the chest, initial symptoms of CO poisoning may include headache, fatigue, dizziness, drowsiness or nausea. Sudden chest pain may occur in people with angina. During prolonged or high exposures, symptoms may worsen and include vomiting, confusion and collapse in addition to loss of consciousness and muscle weakness.


Symptoms vary widely from person to person, according to OSHA. CO poisoning may occur sooner in those most susceptible: young children, elderly people, people with lung or heart disease, people at high altitudes, or those who already have elevated CO blood levels, such as smokers. Also, CO poisoning poses a special risk to fetuses. CO poisoning can be reversed if caught in time. But even if you recover, acute poisoning may result in permanent damage to the parts of your body that require a lot of oxygen such as the heart and brain. Significant reproductive risk is also linked to CO.

Threshold limit value is the maximum concentration of a chemical allowable for repeated exposure without producing adverse health effects.

In the tank test mentioned above, my air monitor tested the CO concentration inside this tank at 2,600 ppm. It looked completely safe. If it wasn’t for my air monitor, I would have gone inside. An Iowa State University report shows just how dangerous the conditions were inside that tank:

  • More than 2 ppm raises questions about why CO is elevated; source should be identified and might be normal, such as traffic or kitchen range
  • 9 ppm is the threshold limit value for an eight-hour period in any year
  • 50 ppm is when most fire departments require self-contained breathing apparatus
  • 800 ppm causes dizziness, nausea and convulsions within 45 minutes, unconsciousness within two hours and death within two to three hours
  • 1,600 ppm causes headache, dizziness and nausea within 20 minutes, death within an hour
  • 6,400 ppm causes headache, dizziness and nausea within one to two minutes, death within 10-15 minutes
  • 12,800 ppm causes death in one to three minutes

So with my air monitor registering CO at 2,600 ppm, if I were to go in I would begin having symptoms in 10-15 minutes. If I didn’t get out and be administered pure oxygen by a paramedic, death would result in about an hour or less. Maybe 45 minutes.


Properly ventilate your tank with an OSHA-approved ventilation fan and ductwork. The fan and ductwork we purchased for about $150 delivers 1,590 cubic feet of fresh air per minute. Most vacuum truck units pull air in at 260-500 cubic feet per minute. Also remember that OSHA requires air to be forced into the confined space and not vacuumed out. Whatever you do, do not blow air in from your truck, as the oil in the air will be atomized and can coat your lungs, causing shortness of breath and could lead to death.

So let’s do some math. A 1,000-gallon septic tank has approximately 140 cubic feet of volume. At 1,590 cubic feet of air transfer per minute, that air will be completely changed out in 8.8 seconds. It’s pretty standard to let the ventilation system work for 15 minutes. How many times will that air have been changed out in 15 minutes? The air would have been changed out 102.3 times with 23,850 cubic feet of air that has been blown in.

When we enter a vacuum tank or a septic tank, we are using a tripod, harness, air monitors, air blowers, winches and rescue cables. There is an entrant, attendee and supervisor on site. My attendee has his hand on the winch and watches the gas monitor. The supervisor is there to bring tools or run errands while I’m in the tank.

Tripods are used in our septic tank entry. On vacuum tank entry we wear the harness and it’s secured to a rope out of the 36-inch manway on the back of the truck. In case of an emergency, the attendee and supervisor will pull out the entrant.

You have to pay attention to how you’d get a worker out of a vacuum tank. Some trucks don’t have a rear manway, only one on top of the tank. In that case, there needs to be a rescue system in place to be able to pull the entrant out from above.


Always use a gas monitor and remember that continuous monitoring is required during work. Confined spaces are to be taken very seriously and all employees helping/assisting on site must be certified. Remember that this is just one example of the criteria and what can go wrong when entering a confined space. Get trained, get certified, and be safe.

Next month, we will explore the steps for a thorough vacuum tank inspection and how knowing these confined space entry rules plays an important role in the process.


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