DTH Drilling at High Altitude: Compressor Derating, Airflow, and Hammer Setup

Quick answer: high altitude changes a DTH drilling system mainly through the air supply. As elevation rises, ambient pressure and air density fall. A portable compressor therefore may deliver less usable mass flow, its engine or motor may have less available power, and its cooling margin can change. If the compressor can no longer supply the hammer’s required pressure and airflow at the actual site conditions, penetration and cuttings evacuation can suffer even though the hammer and bit themselves are unchanged.

The correct response is not to apply one universal altitude correction to every DTH hammer. Confirm the job-site elevation and temperature, obtain the compressor manufacturer’s altitude-rated pressure-flow data, compare that corrected output with the exact hammer requirement, and include hose losses, leakage, drilling depth and flushing demand. This guide explains what changes at altitude, what does not, and what a quarry, mine, contractor or buyer should verify before mobilizing or ordering a DTH drilling system.

Why altitude changes DTH drilling performance

A DTH hammer converts compressed-air energy into repeated piston impacts directly behind the bit. The same air then helps carry cuttings up the annulus. That makes the compressor part of the drilling system, not just a separate utility.

At higher elevation, the compressor starts with lower-density inlet air. Atlas Copco’s current high-altitude guidance explains that portable compressors take in less air mass as density falls, while compressor, engine and cooling performance can all be affected. Its 2025 field example notes that a machine rated at 1,000 CFM at sea level may deliver about 850 CFM at 2,000 m under the example conditions. That 15% example is not a universal correction factor; actual derating depends on compressor design, power source, ambient temperature and the manufacturer’s rating method.

1. Separate compressor nameplate flow from site-available flow

A common planning error is to compare a hammer’s air requirement with the compressor’s sea-level catalog number and assume the match is complete. The relevant question is: what pressure and airflow can this compressor deliver at the site elevation, temperature and duty point?

Atlas Copco’s compressor-dimensioning guidance identifies altitude, ambient pressure, temperature, humidity, compressor type and power source as inputs that can change maximum working pressure, capacity, power consumption and cooling requirement. For a DTH application, the compressor supplier should therefore provide corrected data for the intended elevation rather than asking the drilling crew to derive one generic percentage from an internet table.

When reviewing a compressor sheet, also confirm how flow is stated. Terms such as FAD, CFM and m³/min can be referenced to different conditions. Do not compare two numbers until the reference basis is understood. The DTH hammer manufacturer’s air-consumption table and the compressor supplier’s corrected delivery data need to be interpreted on compatible conditions.

2. Pressure and airflow solve different problems

Pressure and airflow are related but they are not interchangeable.

• Pressure is required for the hammer’s pneumatic cycle and determines the energy available to drive the piston within the hammer’s design range.
• Airflow must be sufficient both to operate the hammer and to transport cuttings through the return annulus.

A compressor can be capable of reaching a target pressure while still having insufficient delivered flow for a particular hole diameter, depth or flushing condition. Conversely, a large nominal flow number does not prove that the required pressure can be maintained at the drill.

Epiroc’s COP M-series guidance explicitly notes that DTH hammers can be adjusted for different compressor air pressures and air volumes, and identifies mines operating at different altitudes as one use case. The practical lesson is not that operators should improvise internal hammer settings. It is that altitude can change the air-supply match enough that the exact hammer configuration and compressor operating point should be checked together.

3. Do not confuse gauge pressure with absolute pressure

Altitude also makes pressure terminology more important. A site gauge normally reads pressure relative to the local atmosphere. Compressor pressure ratio, however, depends on absolute inlet and discharge pressures. Because ambient absolute pressure falls with elevation, maintaining the same gauge working pressure can require a higher compression ratio.

This is one reason the same compressor package may not behave identically at sea level and at a mountain mine. Buyers should not attempt to compensate by simply increasing the gauge setting. Confirm the compressor’s allowable working envelope and the hammer’s approved operating range from the relevant manufacturers.

4. Check the full air path, not only the compressor

Altitude derating can expose losses that were tolerable at lower elevation. A system with little capacity margin may become unstable when hoses, couplings, filters, valves or drill-pipe passages add pressure drop or leakage.

Before blaming the hammer, inspect the full path:

1. Compressor corrected flow and pressure at actual elevation and ambient temperature.
2. Receiver, hose and manifold restrictions.
3. Quick couplings, valves and hose joints for leakage.
4. Drill-pipe internal diameter and connection condition.
5. Hammer inlet, check valve and internal passages according to the service manual.
6. Bit flushing holes for obstruction.
7. Cuttings return at the collar during steady drilling.

Long hose runs and small-bore restrictions are especially important because the pressure seen at the compressor outlet is not necessarily the pressure available at the hammer. If possible, measure the relevant operating pressure at a point that represents the drill inlet rather than relying only on the compressor panel.

5. Hole diameter, depth and cuttings load still determine flushing demand

Altitude does not replace the normal DTH sizing rules. Hole diameter, bit diameter, drill-pipe OD, annular clearance, depth, water, cuttings size and penetration rate still influence the air required to clean the hole.

That means a compressor that works acceptably with one hammer and bit at altitude may be inadequate after the operation moves to a larger hole or deeper drilling program. The higher-elevation site has less margin, but the root requirement still comes from the drilling system and the material that must be transported out of the hole.

For current PerfoMax DTH-bit selection, the safe starting point remains the exact hammer shank, target hole diameter, rock condition, face/button configuration and flushing requirement. See the current DTH Drill Bit Selection page and DTH Tools collection. Compressor sizing must then be verified against the chosen hammer and site conditions; PerfoMax does not replace the compressor manufacturer’s altitude-rating data.

6. A field workflow for high-altitude DTH setup

1. Record the real site condition. Elevation, typical daytime temperature, extreme temperature, humidity where relevant and whether the rig works continuously or intermittently.
2. Lock the drilling configuration. Hammer make/model, shank, bit diameter, hole diameter, pipe OD/ID, planned depth and expected rock/water condition.
3. Obtain the hammer requirement. Use the manufacturer’s pressure-air-consumption data for the exact hammer, not an inch-class estimate.
4. Obtain the compressor altitude curve. Ask for corrected capacity and maximum working pressure at the intended elevation and temperature.
5. Add system losses and margin. Consider hoses, manifolds, leakage, drill-string restrictions and the flushing demand of the hole.
6. Establish a baseline after mobilization. Record pressure, penetration rate, RPM, cuttings return, compressor load and any temperature or shutdown warning.
7. Diagnose before changing settings. If performance falls, distinguish compressor limitation from leakage, bit wear, blocked flushing, ground change or drill-string problems.
8. Change only within approved limits. Do not exceed compressor or hammer ratings to recover sea-level performance.

Typical symptoms when the air system is marginal at altitude

Common planning mistakes

• Buying from nominal CFM alone. The same catalog flow is not automatically available at every elevation and working pressure.
• Using a universal altitude percentage. Derating depends on compressor design, engine/motor, temperature and operating point.
• Ignoring the hammer’s exact air table. A nominal 4-inch or 5-inch class is not enough to establish demand.
• Assuming pressure proves flow. A gauge may show target pressure while cuttings transport is still inadequate.
• Forgetting distribution losses. Hoses, couplings and leakage consume valuable margin.
• Compensating by exceeding ratings. Raising pressure above approved limits can create equipment risk without solving the underlying mismatch.
• Changing bit/hole diameter without recalculating air demand. Flushing requirement changes with the drilling geometry.

What to send in an RFQ for a high-altitude DTH project

To reduce configuration risk, provide both drilling and site data:

• Job-site elevation above sea level
• Expected ambient-temperature range
• Rig make/model and rotary-head connection where relevant
• Exact DTH hammer make/model and bit-shank drawing
• Target hole diameter, depth and inclination
• Drill-pipe OD, ID/air passage and connection
• Rock type, hardness/abrasivity and fracture condition
• Water condition and expected flushing challenge
• Compressor model, rated working pressure and catalog flow
• Manufacturer’s altitude-corrected compressor performance at the project elevation
• Hose length/diameter and any manifolds or auxiliary air users
• Current penetration rate and any high-altitude performance problem if replacing an existing system

PerfoMax can use the drilling-interface and rock information to help confirm the DTH tool configuration. For a technical review, request a quote and include the altitude and compressor data with the hammer/shank information.

Frequently asked questions

How much compressor capacity is lost at high altitude?

There is no universal percentage. Atlas Copco gives a current example in which a 1,000 CFM machine at sea level may provide about 850 CFM at 2,000 m, but the manufacturer explicitly treats altitude performance as equipment-specific. Use the correction curve or rated data for the exact compressor, power source, temperature and working pressure.

Should I increase DTH hammer pressure at altitude?

Not automatically. The hammer must remain within its approved operating range, and the compressor must be able to supply the required flow at that pressure. If output is poor, first verify corrected compressor capacity and pressure loss through the air path.

Does a DTH hammer itself need a different size at high altitude?

Altitude alone does not determine hammer size. Hole diameter, drilling objective, rock and available pressure-flow capacity still drive the selection. However, a hammer that is feasible at sea level may be poorly matched to the same compressor at a much higher site if corrected air capacity is insufficient.

Why can cuttings return get worse even when the pressure gauge looks acceptable?

Because pressure and flow are different requirements. The system may reach pressure but lack enough airflow for the hammer plus annular cuttings transport, or pressure may be lost downstream of the gauge through restrictions and leakage.

What is the single most important number to ask the compressor supplier for?

Ask for the available flow at the required working pressure under the actual project elevation and temperature, together with any maximum-pressure or duty restrictions. A sea-level free-air-delivery number by itself is not sufficient for a high-altitude DTH decision.

Technical references

1. Atlas Copco — How high altitude affects air compressor performance, July 2025.
2. Atlas Copco — Dimensioning Compressor Installations at High Altitude.
3. Epiroc — COP M-series DTH hammers.
4. TerraRoc — QL Series DTH Hammers Technical Manual.