What Is a Bump Test and Why It Matters

If you use a portable gas detector on the job, you’ve probably heard the term bump test more times than you can count. But many safety managers still underestimate its importance.

A bump test (sometimes called a function check) is the process of exposing your gas detector to a known concentration of calibration gas to make sure each sensor and alarm responds properly. It’s the fastest and most reliable way to confirm that your monitor will actually warn you before an atmosphere turns dangerous.

The Occupational Safety and Health Administration (OSHA) considers this a critical step in any confined-space, hazmat, or industrial safety program. Their 2024 Safety and Health Information Bulletin makes it clear: workers must verify detector accuracy before each day’s use. A device that powers on but fails to detect gas is just as dangerous as not having one at all.

OSHA and ISEA: What the Standards Say

Both OSHA and the International Safety Equipment Association (ISEA) have released guidance that defines how often and how thoroughly you should test your monitors:

• Bump Test / Function Check: Verify operation before each day’s use.
• Calibration Check: Compare readings against a known, traceable gas concentration.
• Full Calibration: Adjust the sensor output to match the calibration gas value when a bump test fails or after environmental exposure.

According to ISEA, any gas detector that fails a bump test must be recalibrated before further use. The logic is simple: gas sensors drift. Electrochemical cells age, catalytic beads get poisoned, and dust or humidity can throw readings off.

At Ideal Calibrations, we see this daily. Monitors that haven’t been tested often drift from true values, enough to trigger false alarms or, worse, miss real hazards.

Calibration Drift: The Silent Failure

Calibration drift occurs when a sensor’s baseline shifts over time. Even high-end detectors from BW Technologies, MSA, RKI, and Industrial Scientific experience it. Drift can be caused by:

• Long-term exposure to target gases
• Extreme temperatures or humidity
• Silicone, solvent, or phosphate contamination
• Sensor aging or electronic drift

When that happens, your monitor may still “work,” but its readings become unreliable. A detector that reads 20.3% O₂ in clean air might actually be seeing 20.9%. An LEL sensor that shows 0% LEL may fail to read Methane when exposed in a confined space.That difference can determine whether a confined-space entry is safe or fatal.

The only solution is routine bump testing and calibration with NIST-traceable gas.

How to Perform a Proper Bump Test

Performing a bump test takes less than a minute, but only if you have the right tools. Here’s how to do it correctly.

1. Check Cylinder Information

Before you start, look at your calibration gas label. Confirm:

• Cylinder composition matches your monitor (e.g., 25 ppm H₂S, 100 ppm CO, 50% LEL CH₄, 18% O₂ for BW detectors).
• Cylinder has not expired (typically 48 months for non-reactive gases, 24 months for reactive gases like H₂S, 6-12 months for highly reactive gases like Cl₂).
• Cylinder is stored at room temperature (gases with low vapor pressures can drop out when stored cold)

If the gas is expired or stored in a truck, replace it as expired gas creates false confidence. (Read more in our blog Why Does Calibration Gas Expire?)

2. Attach a Fixed-Flow Regulator

Use a fixed-flow regulator for diffusion monitors or a demand-flow regulator for pumped monitors. This ensures gas enters the sensor at the correct pressure and flow rate. Over-pressurizing can lead to elevated readings; too low of a flow rate can lead to insufficient gas for calibration and future false positives.

3. Apply Gas and Observe

Connect the calibration cup to the detector and apply gas for about 30 seconds. You should see each sensor respond and the alarms activate. If a sensor fails to respond or reads significantly off, perform a full calibration.

4. Record Results

Always log the bump test date, time, gas lot number, and technician’s initials. Use Ideal’s free Gas Detector Bump and Calibration Log to stay compliant and organized.

Bump Test vs. Full Calibration

Test Type	Purpose	Frequency	What You Need
Bump Test (Function Check)	Confirms gas reaches sensors & alarms work	Daily or before each use	Calibration gas + regulator + cal cup
Calibration Check	Compares reading to known gas value	When bump test seems off	Calibration gas + regulator + cal cup
Full Calibration	Adjusts sensor response to match gas value	Monthly or after failed bump test	Calibration gas + regulator + cal cup

The rule of thumb: bump daily, calibrate monthly.

When to Calibrate Immediately

Certain conditions require a full calibration right away, even if the detector passed yesterday’s bump test:

• After exposure to high gas concentrations (over-range readings)
• After battery replacement or sensor change
• After impact or immersion in liquid
• After storage in extreme heat or cold

If your monitor fails to zero, shows slow response, or won’t hold calibration, send it in for professional service. Ideal Calibrations offers full diagnostic and repair service for most brands, including MSA Altair, BW Technologies, Industrial Scientific, RKI, and Honeywell. You can download our service form here.

Common Mistakes During Bump Testing

1. Using Expired Gas: Reactive components like H₂S fade quickly in steel cylinders. Use aluminum for non-reactive mixes and stainless steel for reactive ones. (See our article Why Calibration Gas Expires/Fades.)
2. Leaving Regulators Attached: Always remove the regulator after use to prevent seal contamination.
3. Incorrect Flow Rate: Using a 3 LPM regulator on a diffusion monitor can trigger false alarms and waste gas.
4. Skipping Logs: If it’s not recorded, it didn’t happen — and OSHA auditors know it.
5. Calibrating in Poor Air: Always perform fresh-air zero away from running equipment or vehicle exhaust.

The OSHA Bottom Line: Safety Through Verification

OSHA’s message is simple; verify before you work. Gas detectors save lives only when their sensors are accurate. Skipping a 30-second bump test can turn a life-saving tool into a false sense of security. As OSHA puts it, “Instrument inaccuracy due to improper or irregular maintenance and calibration can lead to exposure to hazardous levels of toxic gases or to oxygen-deficient or flammable atmospheres. This exposure can cause workers to suffer serious injuries or illness, and even death. Flammable gas explosions are often catastrophic, resulting in worker injuries and death, or destruction of property.” That’s not a risk worth taking.

Ideal Calibrations: Your Partner in Accuracy

At Ideal Calibrations, we don’t just sell gas we build confidence in your equipment. Our Ideal Gases calibration cylinders are:

• NIST-traceable for metrological accuracy
• Compatible with all major brands (BW, MSA, RKI, ISC, Honeywell, etc)
• Available in custom mixes and sizes to fit your fleet
• Backed by real technicians, not automated support from foreign countries

We also offer calibration and repair services from our facilities with turnaround times as fast as 3 days.

Ready to Stay Compliant?

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Whether you’re prepping for OSHA audits or keeping your crew safe, Ideal Calibrations has the gas, gear, and guidance you need.-