NFPA 110 Generator Fuel Testing

In September 2017, a Florida nursing home lost air conditioning after Hurricane Irma knocked out power. The backup generator failed—not because of mechanical problems, but because degraded fuel couldn't sustain operation. Twelve residents died in the sweltering heat that followed.

That tragedy wasn't an isolated incident. Survivors of Superstorm Sandy and Hurricane Katrina tell similar stories: generators that should have worked, fuel that should have been ready, systems that failed when they were needed most. The common thread running through these failures isn't equipment age or poor maintenance scheduling. It's fuel that sat in storage tanks slowly degrading until the moment it was called upon to perform.

NFPA 110 exists because the National Fire Protection Association recognized this reality. The standard establishes minimum requirements for emergency and standby power systems, and Section 8.3.7 specifically addresses fuel quality: A fuel quality test shall be performed at least annually using appropriate ASTM standards.

That sounds straightforward enough. But facility managers often discover the complexity hiding beneath that simple requirement when an inspector shows up or when their generator fails to start during an actual emergency.

What Does NFPA 110 Actually Require for Fuel Testing?

The standard itself doesn't prescribe a specific test package. Instead, it references ASTM D975—the specification for diesel fuel oils—and leaves some interpretation to the Authority Having Jurisdiction (AHJ). This flexibility can be helpful, but it also creates confusion about what "appropriate ASTM standards" really means for your facility.

The appendix sections of NFPA 110 provide additional guidance, recommending that fuel testing pay special attention to sampling the bottom of storage tanks to verify fuel is "as clean and dry as practicable" and free from water, sediment, or microbial contamination. This language matters because it establishes the intent: your fuel should be ready to perform when called upon, not just technically present in the tank.

For Level 1 systems—those where failure could result in death or serious injury, such as hospitals—the stakes are higher and the scrutiny more intense. Level 2 systems have somewhat more flexibility, but the fundamental requirement remains: annual fuel testing using recognized ASTM methods.

Which ASTM Tests Should You Run?

ASTM D975 contains twelve different test parameters, and running all of them every year would be expensive and largely unnecessary. The key is selecting tests that evaluate the properties most likely to cause problems in stored fuel used for emergency generation.

A practical approach focuses on two categories: tests that confirm combustion properties (will this fuel actually run your engine?) and tests that identify contamination (is something in this fuel likely to cause damage or failure?).

Tests That Confirm Combustion Properties

The D86 Distillation test measures the boiling point range of your fuel components. If the distillation curve is off-spec, the engine may run roughly, produce excessive smoke, or fail to start entirely.

D93 Flash Point determines the minimum temperature at which fuel vapors will ignite—a safety parameter, but also an indicator of contamination or degradation.

D976 Cetane Index evaluates ignition quality, which directly affects starting performance, particularly in cold weather.

Tests That Identify Contamination

D2709 Water & Sediment uses centrifugation to measure combined water and particulate contamination. Healthy diesel should contain less than 0.05% combined water and sediment.

D6304 Water by Karl Fischer provides a more precise measurement of dissolved water content, detecting down to parts per million.

D2622 Sulfur Content verifies your fuel meets the 15 ppm maximum for ultra-low sulfur diesel. This isn't "contamination" in the classic sense, but it does indicate an excess presence of something that is controlled by regulation—critical for protecting diesel particulate filters on newer generators.

Tests That Predict Future Problems

D130 Copper Strip Corrosion evaluates the fuel's potential to corrode metal components in your fuel system.

D2274 Oxidation Stability subjects fuel to accelerated aging conditions to predict how it will behave during extended storage.

The Mission Critical Test Slate Approach

Rather than piecing together individual tests, many facility managers find value in a comprehensive test package specifically designed for emergency generator applications. Bell Performance's Mission Critical test slate includes D86 Distillation, D93 Flash Point, D130 Copper Strip Corrosion, D287/D4052 API Gravity, D976 Cetane Index, D2709 Water & Sediment, D6304 Water by Karl Fischer, and D2622 Sulfur Content.

This combination addresses Joint Commission compliance requirements for healthcare facilities while providing the combustion and contamination data needed to genuinely assess fuel readiness. Running these tests individually at an accredited lab can cost upward of $2,000, though partnering with a fuel management specialist who has existing lab relationships can reduce that cost significantly.

NFPA 110 Testing Frequency Requirements at a Glance

What About Microbial Testing?

Here's where NFPA 110's language about fuel being "clean and dry" intersects with practical reality. The standard doesn't explicitly mandate microbial testing, but microbes are the single most common cause of stored fuel problems. They establish colonies at the fuel-water interface, produce acidic byproducts that accelerate corrosion, and generate biomass that clogs filters at the worst possible moments.

ATP-by-Filtration testing (ASTM D7687) provides quantitative measurement of microbial activity in fuel samples. Unlike older culture-based methods that take days or weeks, ATP testing delivers results within hours. For facilities storing fuel for extended periods—which describes virtually every emergency generator application—quarterly microbial monitoring fills a gap that annual ASTM specification testing doesn't address.

The logic is straightforward: annual testing tells you whether your fuel met specifications on the day you sampled it. Quarterly microbial monitoring tells you whether conditions are developing that will cause your fuel to fail before the next annual test.

Sampling Matters More Than You Think

Testing accuracy depends entirely on sample quality. Most fuel testing labs recommend pulling samples from three to six inches off the tank bottom—above where contamination typically settles, but low enough to detect problems before they reach your fuel pickup.

The proper tool for this job is a fuel sampler (industry professionals call it a "Bacon Bomb"), which allows you to collect samples from specific depths without disturbing sediment or cross-contaminating the sample. Pulling a sample from the top of the tank might give you clean-looking fuel that tells you nothing about what's happening where problems actually develop.

Poor sampling technique is responsible for a surprising number of both false positives (failing tests on fuel that's actually fine) and false negatives (passing tests on fuel with serious contamination sitting below the sample point). If your test results don't match what you're observing in your system's performance, sampling location is the first variable to examine.

What Happens When Your Fuel Fails?

Test results tell you what's wrong. Fixing the problem usually requires combining chemical treatment with mechanical intervention—what Bell Performance calls the "hybrid approach." Neither solution works as well in isolation as they do together.

Failed Water & Sediment or microbial tests typically call for both mechanical fuel polishing (filtration to physically remove contamination) and chemical treatment (biocide like Bellicide or ClearKill to eliminate active microbial growth, plus water controllers to prevent recontamination). The polishing removes what's already there; the chemistry prevents it from coming back. Skip the biocide treatment and you'll be polishing again in six months. Skip the polishing and biocide alone can't remove the biomass that's already clogging your filters.

Failed Stability tests indicate the fuel is oxidizing faster than normal—producing gums, varnishes, and sludge that settle throughout your system. Mechanical polishing removes existing degradation products, while stabilizer treatment with a product like Dee-Zol Life slows future breakdown. The fuel may still be usable, but storage life will be limited without ongoing chemical protection.

Failed Distillation or Cetane tests suggest the fuel may not support proper combustion. Depending on severity, dilution with fresh fuel may be possible. These are situations where chemistry can't help—you're dealing with fundamental fuel composition issues that require mechanical solutions (fuel replacement or blending).

Failed Sulfur Content tests present the most difficult situation. There's no practical chemical or mechanical solution for removing sulfur from diesel fuel. Dilution might work if you're only slightly over the 15 ppm limit, but significant sulfur contamination usually means disposal and replacement.

The cost calculation always favors testing over assuming. A full Mission Critical test slate costs a few hundred dollars through a fuel management partner with established lab relationships. Disposing of 500 gallons of fuel you assumed was bad costs $2,500 to $10,000 depending on your location. Having your generator fail during an actual emergency? That cost is measured in ways that go far beyond money—as those Florida families learned in the worst possible way.

Documentation for Inspectors and Auditors

Beyond the testing itself, NFPA 110 compliance requires maintaining detailed records of test results, treatment applications, and system maintenance. Inspectors expect to see a paper trail demonstrating ongoing attention to fuel quality—not just a single passing test from last year.

Effective documentation includes test results with dates and sample locations, treatment logs showing what products were applied and when, trending data that shows fuel condition over time, and corrective action records when problems were identified. For healthcare facilities subject to Joint Commission review, this documentation isn't optional. Inspectors specifically look for evidence that fuel quality is being actively managed rather than passively ignored until problems develop.

A Practical Compliance Approach

For most facility managers, the path to NFPA 110 compliance involves establishing a testing program that meets the minimum annual requirement while providing enough visibility to catch problems between tests. A workable framework looks like this:

Conduct annual Mission Critical ASTM testing to document overall fuel condition and maintain compliance records. Add quarterly ATP microbial testing to monitor the most common failure mode for stored fuel. Perform monthly visual inspections during your regular generator load tests—you're already there, so checking fuel appearance and water detection devices adds minimal time. Maintain treatment logs and test result history for inspector review and trending analysis.

The goal isn't to test constantly—it's to test strategically so you know what's in your tanks and can address problems before they cause failures.

Ready to simplify your NFPA 110 fuel compliance? The Fuel Secure subscription program from Bell Performance includes annual Mission Critical ASTM testing, ATP microbial monitoring at your chosen frequency, sampling equipment, and expert treatment recommendations when needed. With more than 115 years of fuel chemistry expertise behind every recommendation, you're not just getting test results—you're getting a partner who understands what those results mean and what to do about them. Contact Bell Performance at 407-831-5021 to discuss your facility's specific requirements.

Downloadable: NFPA 110 Fuel Testing Compliance Checklist

Weekly

• Visual inspection of fuel system components
• Check water detection devices (if installed)
• Note any unusual odors near fuel storage

Monthly

• Conduct 30-minute load test at minimum 30% of nameplate rating
• Document load achieved and runtime
• Visual check of fuel sample for clarity and color

Quarterly (Recommended)

• ATP microbial testing of fuel sample
• Sample from 3-6 inches off tank bottom
• Compare results to previous quarter for trending

Annually

• ASTM D975 specification testing (Mission Critical slate or equivalent)
• Sample from 3-6 inches off tank bottom
• Document all test results for compliance records
• Apply corrective treatments if any tests fail specification
• Update treatment log with any applications

Every 36 Months (Level 1 Systems)

• Full system extended run test
• Load at actual building load or 30% of nameplate (whichever is greater)

Documentation to Maintain

• All test results with dates and sample locations
• Treatment application log
• Corrective action records
• Fuel delivery receipts
• Generator maintenance records