Solving Two Fire Risks on One Machine: Hybrid Scissor Lifts

Hybrid scissor lifts that combine a lithium-ion battery with a diesel engine are becoming more common on tunnel and underground construction sites, where operators want the flexibility to run electric power indoors or in sensitive areas and switch to diesel power where that makes more sense for the job. From a fire protection standpoint, this hybrid design creates a genuinely harder problem than either power source presents on its own. A hybrid machine does not have one fire risk to protect against. It has two, sitting in different compartments on the same piece of equipment, each with its own failure mode and its own suppression requirements.

Why Hybrid Equipment Is a Different Kind of Challenge

A standard diesel scissor lift has the engine compartment fire risk common to most combustion equipment: hot surfaces, fuel and hydraulic lines, and electrical wiring in a confined space. A standard lithium-ion powered lift has battery compartment risk instead, centered on thermal runaway and the gas that a stressed or failing lithium battery can release before a visible fire even starts.

A hybrid machine has both, and they are not interchangeable problems. The diesel side calls for the kind of heat activated suppression that protects any combustion engine compartment. The battery side calls for something more specific: a way to detect the earliest signs of a battery fault, ideally before it progresses to the point of open flame, since lithium battery events can escalate very quickly once they start.

What BlazeCut Is Building for This Application

BlazeCut is currently developing a combined suppression approach for exactly this hybrid scenario, built around protecting both compartments on the same machine rather than treating it as two unrelated problems. The diesel side uses the same T Series heat sensitive tube technology already proven across engine compartments in other equipment categories. The battery side adds an off-gas detector, designed to pick up on the gas a lithium battery releases as it begins to fail, ahead of the point where a standard heat sensor would first respond.

Pairing these two elements on one machine means the suppression strategy matches the actual risk in each compartment rather than applying a single generic approach to both. The diesel engine bay gets heat based detection suited to a combustion fire. The battery compartment gets earlier stage detection suited to how a lithium fault typically develops, which matters given how much faster a battery event can move once it is underway.

Where This Stands Today

It is worth being direct about where this application currently sits. This combined system is in the process of gaining site approval, and that process is a real one. Most tunnel sites currently maintain a cautious, often outright restrictive posture toward lithium-ion battery equipment of any kind, given the difficulty of controlling a battery fire underground and the limited egress that makes any underground fire more serious than the same event on the surface. Getting a hybrid machine with a lithium component approved for underground use requires demonstrating that the fire risk has been addressed seriously, not just adequately.

That is the case being built with this combined T Series and off-gas detection approach: rather than asking a site to accept a lithium battery on faith, the goal is to show a specific, engineered response to the specific failure mode a hybrid machine presents. This is genuinely new ground for the tunneling industry, and the approval process reflects how seriously sites are treating lithium risk underground, which is exactly the right posture for them to take.

Why This Matters for Equipment Owners and Site Safety Teams

For an equipment owner considering hybrid lift equipment on future underground projects, or a site safety officer being asked to evaluate one, this combined approach is a preview of where fire protection for hybrid and battery electric equipment is headed. As more equipment categories move toward electrification, even in combination with existing combustion power, suppression strategies will need to address both power sources at once rather than treating electrification as a simple substitution. Being early to that conversation, with a concrete engineering approach already in development, is useful information for anyone planning a future fleet decision around hybrid equipment.

Frequently Asked Questions

Why does a hybrid diesel and lithium-ion machine need a different approach than either power source alone? Because it has two separate fire risks in two separate compartments, a combustion engine fire risk and a battery fault risk, each of which develops differently and calls for a different kind of detection and response.

What does the off-gas detector add that heat detection alone does not? A lithium battery releases gas as it begins to fail, often before enough heat has built up to trigger a standard heat sensor. Off-gas detection is intended to catch that earlier stage, which matters because lithium battery events can escalate quickly once underway.

Is this system currently approved and in use on tunnel sites? It is in the process of gaining site approval. Most tunnel sites currently take a cautious approach toward lithium-ion equipment given the added risk of a battery fire underground, and this combined approach is being evaluated as part of that process.

Can this same combined approach apply to other hybrid equipment beyond scissor lifts? The underlying principle, pairing heat based detection for a combustion compartment with off-gas detection for a battery compartment, applies to other hybrid equipment configurations facing the same dual fire risk.

Should equipment owners consider this now if they are not currently running hybrid equipment on underground projects? It is worth understanding as fleet electrification continues, since more equipment categories are likely to introduce battery components in some form, and planning for that fire risk early is easier than retrofitting a response after equipment is already in service.

If you are evaluating hybrid or battery electric equipment for underground or civil construction use, email Dalton at dalton@blazecutusa.com to discuss where this technology stands and what it could mean for your fleet.

Note: Names and identifying details referenced in this article have been changed to protect the privacy of the companies involved.