Safety
Mobile work strips away everything a shop gives you for free: a level concrete floor, a lift, controlled access, and coworkers who can call for help.
- Chocks on the downhill side prevent the vehicle from rolling further downhill if the jack fails. On an incline, you should NEVER trust the parking brake alone, and moving the vehicle isn't always practical.
- Two jack stands on manufacturer-rated jack points is the minimum for safe undercar work. The jack itself is NEVER a safety device — always use jack stands. Placement should always match the vehicle's structural jack points.
- Creating a visible work perimeter with cones prevents other vehicles and pedestrians from entering your workspace. This protects both you and them, and it's a professional standard that also serves as visual signage that you're working.
- Leaning jack stands are a fatal accident waiting to happen. There is no scenario in which continuing work is acceptable. Exit, correct, and re-verify placement before continuing.
- Children near working vehicles are a safety catastrophe. The professional immediately stops, involves the parent respectfully, and doesn't resume until the situation is safe. Never work around unsupervised children.
- The most common breaker bar injury is a slipped fastener causing the bar to swing through the operator's hand or face. Body position — never in the swing path — is the primary defense. Gloves help with grip but don't prevent this.
- Whenever you're inside the engine bay, physically remove the key/keyfob and keep it in your possession. Verbal instructions to customers get forgotten. This has prevented countless serious injuries.
- Disconnecting the battery prevents welding current from damaging vehicle electronics. Covering fuel components with a fire blanket prevents ignition. Both are non-negotiable before hot work on a vehicle.
Every driveway, parking lot, and highway shoulder is a new job site you have to make safe yourself, and the habits in this lesson are what keep a routine brake job from turning into a crushing injury or worse.
Lifting and Supporting Vehicles in the Field
Driveways are almost never level, and that changes your setup before you touch a jack. On any incline, chock the wheels that will remain on the ground, and place those chocks on the downhill side. The reasoning is simple: if the jack fails or the vehicle shifts, gravity pulls it downhill, and downhill chocks are what stop the roll. Never trust the parking brake alone on an incline — parking brakes fail, cables stretch, and rear brakes may be the very thing you are servicing. Asking the customer to move the car to level ground sounds nice but often is not practical, so build your setup around the slope you actually have.
The jack is a lifting tool, never a support device. Before any part of your body goes under a vehicle, it must be resting on jack stands — a minimum of two, placed on manufacturer-rated jack points, and matched to each other in height so the vehicle sits level and stable. Rated jack points are structural; pinch welds, floor pans, and suspension arms that are not designated lift points can crumple or let the stand slip. One stand is never enough for undercar work, and four are not required — two properly placed stands is the professional minimum.
Stay alert to your supports the whole job. If you notice a jack stand leaning, even slightly, there is exactly one correct response: get out from under the vehicle immediately, correct the placement, and re-verify everything before you go back under. The stands have not collapsed yet, and that is precisely the moment to fix it. Propping a leaning stand with scrap wood or having someone steady the car are not solutions — a leaning stand is a fatal accident waiting to happen, and no deadline justifies staying under it.
- Chock the grounded wheels on the downhill side before lifting on any incline
- Lift only at manufacturer-rated jack points
- Set a minimum of two jack stands, matched in height, on rated points
- Lower the vehicle onto the stands and shake-test before going under
- If a stand leans or shifts, exit immediately, correct, and re-verify
Controlling the Work Area
In a shop, walls and bay doors keep traffic out of your workspace. In an apartment complex lot, a strip-mall parking lot, or a customer's street, nothing does — unless you create it. Set up cones or a clearly visible perimeter around your work area before you start. The perimeter does two jobs at once: it physically warns drivers and pedestrians away from your jack stands, tools, and body, and it acts as visual signage that professional work is in progress. High-visibility clothing helps, but it protects only you; the perimeter protects the whole scene, and it is the mark of a professional operation.
Customers' homes bring a hazard shops never see: children. Kids are drawn to tools, jacks, and open hoods. The moment a child approaches your work area, stop working completely. Politely ask the parent to keep the child away, and do not resume until the area is clear and stays clear. Never let a child hold tools or watch from close range, and never just keep wrenching and hope they lose interest. A vehicle on stands, hot components, and power tools around an unsupervised child is a catastrophe you are one distraction away from.
Keeping the Vehicle from Biting You
Any time your hands are in the engine bay, the vehicle must be incapable of starting. The rule is physical, not verbal: remove the key or keyfob and keep it in your own pocket until you are clear of the engine bay. Telling the customer not to start the car is not a safety measure — verbal instructions get forgotten, a family member grabs the keys, or a remote start fires. An engine that cranks with your fingers near the belt drive or fan is a maiming injury, and physical possession of the key is the practice that has prevented countless of them.
Hand tool technique matters too, and the breaker bar is the classic teacher. When you are hauling on a stubborn lug nut or suspension bolt, the fastener will eventually give way suddenly — that is the whole point of the tool. Plan for that instant before you pull: never position any part of your body in the path the bar will travel if the fastener breaks free or the socket slips. The most common breaker bar injury is the bar swinging through the operator's knuckles or face when a fastener lets go. Gloves improve grip but do nothing to stop a swinging bar; body position is the primary defense.
Hot Work: Welding and Grinding on Vehicles
Occasionally mobile work involves grinding or welding on a vehicle — exhaust hangers, brackets, seized hardware. Two precautions are non-negotiable before any hot work. First, disconnect the negative battery cable. Welding current finds its own path through the vehicle, and without the battery isolated it can destroy control modules and sensors — an expensive lesson in electronics you now own. Second, shield the fuel system: cover fuel lines and the fuel tank so sparks cannot reach them, ideally with a fire blanket. Safety glasses and a fire extinguisher are baseline equipment, but they respond to a fire; disconnecting the battery and covering fuel components prevent one. Do both, every time, before the first spark.
| Item | Standard | Why it matters |
|---|---|---|
| Warning devices, surface street | About 100 ft behind the vehicle | Gives 30-40 mph traffic time to see and move over |
| Warning devices, highway | 200-300 ft behind, more on curves and hills | Highway closing speeds eat distance fast; the device must appear before the scene does |
| Jack stands | Minimum 2, matched height, on manufacturer-rated points | The jack lifts; only stands support a vehicle with a body under it |
| Wheel chocks | Grounded wheels, downhill side, set before lifting | Gravity pulls downhill if anything shifts — downhill chocks stop the roll |
| Key control | Key or fob in your own pocket during engine-bay work | Physical possession is the only start-prevention that survives a forgetful family member or remote start |
| Hot work prep | Negative battery cable disconnected, fuel lines and tank shielded | Prevents fried modules and sparked fuel instead of reacting to them |
Distances are common industry guidance, not law everywhere — some states set their own placement rules, and night or bad weather earns extra distance. Verify local requirements for your service area.
- Park your truck to shield the work area where the layout allows — angled between traffic and the vehicle. Your truck becomes a physical barrier before a single cone comes out.
- Read the slope before unloading anything. The grade you see decides where chocks go and whether the job is safe to do here at all.
- Chock the grounded wheels on the downhill side, then set your perimeter cones. If the chocks want to slide or the cones will not keep traffic off you, that is your answer about the location.
- Ask for the key or fob and put it in your pocket. The vehicle is now physically incapable of starting with your hands in the bay.
- Lift only at rated jack points, set two matched stands, lower onto the stands, and shake-test the vehicle hard. If it moves on the shake, you found the problem standing up instead of lying down.
- Recheck stand contact any time the vehicle takes a shock — breaker bar pulls, impact gun work, a wheel fighting you. Stands that started perfect can walk on asphalt or soft ground.
- Trusting the parking brake as your incline security. Cables stretch, the mechanism fails, and on a brake job the rear brakes may be the exact system you are disassembling — chocks on the downhill side are the real control.
- Sliding under a vehicle held only by the jack "for just a second." Hydraulic seals fail without warning, and a jack was never designed to hold a static load with a person under it. Stands first, every time.
- Telling the customer not to start the car instead of pocketing the key. Verbal instructions get forgotten, a family member grabs the keys, a remote start fires — and an engine cranking with your fingers near the belt drive is a maiming injury.
- Continuing to wrench while a child hovers near the work area. A vehicle on stands, hot parts, and power tools around an unsupervised kid is a catastrophe one distraction away — stop completely until the area is clear and stays clear.
The driveway slopes toward the street and you are replacing rear brake pads. Where do the chocks go, and why is the parking brake not enough?
Chock the front wheels — they stay on the ground — on the downhill (street) side, because gravity pulls the vehicle toward the street if anything shifts. The parking brake acts on the rear brakes, which are the very system you are about to disassemble, so it cannot be your security on this job.
Mid-job you glance over and one jack stand is leaning slightly. The vehicle has not moved. What is the correct response?
Get out from under the vehicle immediately, correct the stand placement, and re-verify the entire setup before going back under. The stand has not collapsed yet — that is exactly the moment to fix it. Propping it with scrap or having someone steady the car are not solutions.
You are about to grind a seized exhaust hanger bolt in a customer's driveway. Name the two non-negotiable steps before the first spark.
Disconnect the negative battery cable, because welding and grinding current can find paths through the vehicle and destroy modules and sensors. Then shield the fuel lines and tank — ideally with a fire blanket — so sparks cannot reach them. Extinguisher and glasses respond to a fire; these two steps prevent one.
The driveway slopes toward the street and you are replacing rear brake pads. Where do the chocks go, and why is the parking brake not enough?
Missed one? The reasoning above comes straight from the MOB exam bank, so this is the standard you will be held to.