The Alberta Fire Code requires that inventory control is done for underground and aboveground storage systems. Inspections carried out by the PTMAA show that many facilities are not performing inventory control in a way that is likely to find leaks or complies with provincial requirements. Hopefully, this fact sheet and accompanying forms and spreadsheets will help you perform this type of leak detection properly.

When is inventory control required?

If your tank system includes a metering system where the product is removed from storage tanks is measured, you must do inventory control. Inventory control is not carried out, for example, on used oil tanks or generator tanks. A reconciliation of inventory must be done each day the tank system operates. Aboveground double-walled tanks do not require inventory control if the interstitial space is monitored monthly and a log of findings is kept. The interstitial space is between the two walls of the tank.  To opt for monthly monitoring instead of daily inventory calculations any connected underground piping must be double-walled and continuously monitored with sensors in the transition sump and under-dispenser sumps.  

How does inventory control work?

Inventory control involves daily manual measurements of tank contents, recording fuel deliveries, metering of fuel pumped, and monthly math calculations that compare the stick inventory (which you have measured) to the book inventory (what your meters and delivery receipts indicate that you should have). If the difference between the two is too large, your tank may be leaking. For underground tanks, too large is greater than 1/2 of 1% of the amount that is pumped from a particular tank. For aboveground tanks too large is greater than 1% of the throughput from the tank.

For inventory control to be successful, three important elements must be present:

  1. Good stick measuring
  2. Good math
  3. Good record keeping

Do you have the right equipment?

Gauge Stick

The gauge stick used to measure the depth of liquid in a storage tank must be marked to the 1/2 cm (with zero at the bottom end). Check your stick to be sure that the end is not worn, broken, shortened, and that the stick is not warped. The stick should be made of a non-sparking material such as wood or fibreglass. Wooden sticks should be varnished to keep the fuel from soaking into the stick and causing false readings. It is important to make sure that the correct gauge chart from the manufacturer is used when converting tank volumes from centimeters to liters.

Pastes for Finding Water

Sudden changes in tank water level may indicate that water is entering the tank through a hole. For underground tanks you must check for water in the bottom of the tank each day by spearing a water-finding paste along the bottom ten centimeters or so of the gauge stick. The paste changes color when it comes in contact with water. Make sure your paste is compatible with ethanol gasoline. A column in the attached monthly inventory record is to be used for recording water checks.

Tank Chart for Converting Centimeters to Litres

You must have a centimeter to liter conversion chart for each tank. A tank chart is specific to a given tank model and capacity. If you do not have a conversion chart for your tank, contact the company that manufactured the tank or the contractor who installed it.

Drop Tube

Each tank must have a drop tube which extends to within one foot of the tank bottom. Stick measurements are made through the drop tube. The drop tube ensures that the stick is straight up and down when measuring and minimizes static buildup and the release of flammable vapors from splashing.

Calibrated Dispensing Meters

All meters must be calibrated according to federal standards. Industry Canada inspectors will periodically check dispensers to ensure that meters are calibrated properly. Tank contractors can also calibrate your meters.


The spreadsheets attached to this fact sheet can be copied and used to record data and perform the daily reconciliation. If you do not want to use a computer to manage your inventory records you can print the sheet at the end of this guide called "Daily Worksheet" and print one copy of the Monthly Inventory Record. Photocopy the Worksheet to use it for all the tanks for each day the tanks operate. You'll need one copy of the Monthly Inventory Record for each tank for each month of the year. If you want to use a computer to manage your inventory the Monthly Inventory Record is on the Excel spreadsheet called Tank 1, Tank 2, etc. Be sure to save the file but rename the file as soon as you start using it for the first month of records. The first month you start using the file, name it the month and year to keep a blank copy available. You must retain paper copies for an inspector to review.

If You Have Manifolded Tanks

Manifolded tanks must be considered a one-tank system because they share a common inventory of stored fuel and all the dispensers connected to the tanks are part of a single system. You will need to combine your measurements and calculations for all manifolded tanks into one system. So, if you have two 25,000 liter tanks connected by manifold, add their volumes together and look for gains and losses in comparison to all dispensers feeding from those two tanks.

What Are the Steps to Performing Proper Inventory Control?

Step 1: Measure the Tank Contents

 At the end of each operating day or at a set time each day, obtain the tank volume by sticking all tanks. Convert centimeters to liters using the tank chart and record both centimeters and liters in the rows labeled End Stick Centimeters and End Stick Liters on a new copy of the Daily Inventory Worksheet. Do not measure when fuel is being added to or removed from the tank. The stick should be read to the nearest 1/2 centimeter. To assist employees who measure tank inventory, copy and post the "Tips for Measuring Tanks" page found at the end of this fact sheet.

Step 2: Record the Amount Pumped

You have to know which dispensers are connected to each storage tank. The bottom of the worksheet has a place where you can record which tank numbers are connected to which pump numbers. This is useful for new personnel doing the reconciliation. At the end of each operating day, record the amount of fuel pumped from each tank. You will likely have to read the totalizor numbers from the dispenser itself but your cash register may give you liters pumped from each dispenser. Record the data in the Liters Pumped Today section of the Daily Inventory Worksheet. Read all the dispensers totalizers and record the readings in the appopriate column for each tank. Add the totalizer readings to determine Today's Sum of Totalizers for each tank. Subtract the Previous Day's Sum of Totalizers for each tank and record the results in the Liters Pumped Today section. Be sure to read the register or the totalizers at the same time as sticking the tanks and make sure no fuel was dispensed during this time.

Step 3: Record Fuel Deliveries

Fuel deliveries must be recorded when they are made. The tank must be gauged by stick, both before and after the delivery. Convert centimeters to liters using the tank chart and record both centimeters and liters in the Delivery Record section of the Daily Inventory Worksheet. Subtract the initial gauge from the end gauge to determine the Liters Delivered (Stick). Record the amount on the delivery receipt from the fuel supplier in the Gross Liters Delivered (Receipt). These numbers should roughly match.

Step 4: Calculate Daily Changes in Inventory

After the intial sticking day, you can start to calculate the daily changes to inventory on the Monthly Inventory Record. Using the numbers from the Daily Inventory Worksheet, first calculate the Book Inventory by adding the Start Stick Inventory (which is the previous day's End Stick Inventory) and the Liters Delivered for the day, if any, and then subtracting the Amount Pumped for the day. Next subtract the End Stick Inventory from the Book Inventory and record the difference in the Daily Over and Short (End Book) column. Record any water detected in centimeters.

Step 5: Calculate Monthly Changes in Inventory

At the end of each month, the overages and shortages must be calculated on the Monthly Inventory Record to determine if the shortages are too great. The following steps will explain how to determine if there could be a leak.

  1. Add all of the month's Liters Pumped numbers and write this total at the bottom of the column in the box labeled Total Liters Pumped. If using the spreadsheet on a computer, it will totalize for you.
  2. Add all the month's Daily Over or Short numbers: Pay careful attention to positive and negative numbers to get an accurate total. If doing this manually, enter an overage using (+) in front of the number. With a loss use (-) in front of the number.  Enter the total at the bottom of the column in the box labeled Total Liters Over or Short. Computer users - this will also total for you.
  3. Fill out the Leak Check line as follows: Take the Total Liters Pumped and multiply by 0.05. Enter the result of this calculation at the end of the Leak Check line. This number is the maximum change in inventory allowed by the Fire Code. (1/2 or 1% of the liters pumped from a particular tank). This will be automatically calculated for computer users.  Total the pluses and minuses from the Daily Over (+) and Short (-) column. Again, the computer will calculate this for you.
  4. At the bottom of the Monthly Inventory Record, check "Yes" or "No" depending whether your Net Liters Over or Short number is larger than the Maximum losses number.
  5. At the end of the month count the number of days you had consecutive losses.
  6. At the end of the month count the total numbers of days you had no losses.

If you indicated "yes" for any of:

  1. net losses greater than 1/2 of 1% (underground tanks),
  2. 3 consecutive losses greater than 200 litres/day, or
  3. greater than 50 mm of water in the tank.

you must call the Authority Having Jurisdiction. You must immediately investigate and resolve all suspected leaks.

What About Water in the Tank?

There is normally a small amount of water in any tank, which may slowly increase over time due to condensation. However, a sudden change in water level, either up or down, may indicate a leaking tank. If you have 5 centimeters or more of water there is a good chance it will get drawn to your dispenser. Arrange to have the water removed and check often for more of it coming into the tank - it could indicate a leak.


These records must be kept at the facility where the tanks are located and be available to an inspector in reasonable time. Records must be retained for at least two years.

If You Need Help

Call the PTMAA office at 1-866-222-8265 and we'll help you out