Mistake recovery pages.
Every mistake has a shareable recovery page with related mistakes, apprentice questions, Field Rescue links, and Ask Foreman wording.
All mistakes
#001 · Not wearing safety glasses during cutting, grinding, or drilling1st Year · Safety#002 · Wearing loose clothing or jewelry around rotating machinery or sharp edges1st Year · Safety#003 · Failing to de-energize equipment before working near it (not following lockout/tagout)1st Year · Safety#004 · Walking on sheet metal without checking if it can support your weight1st Year · Safety#005 · Not using gloves when handling freshly cut sheet metal edges1st Year · Safety#006 · Misreading a tape measure - confusing 1/16" marks with 1/8" marks1st Year · Measuring & Layout#007 · Forgetting to account for material thickness when laying out bends1st Year · Measuring & Layout#008 · Measuring from the wrong reference point on the tape (the hook gap error)1st Year · Measuring & Layout#009 · Not squaring the layout line before scribing, resulting in parallelogram cuts1st Year · Measuring & Layout#010 · Mixing up inside and outside dimensions when reading blueprints1st Year · Measuring & Layout#011 · Cutting too fast on a plasma or snips, creating jagged, uneven edges1st Year · Fabrication#012 · Not deburring sheet metal edges before assembling connections1st Year · Fabrication#013 · Mis-setting brake press stop causing repeated wrong-angle bends1st Year · Fabrication#014 · Using worn or incorrect snips for the direction of cut (left vs right vs straight)1st Year · Fabrication#015 · Cutting on the wrong side of a scribe line and losing dimension1st Year · Fabrication#016 · Not checking that tools are in good working condition before use1st Year · Tools & Equipment#017 · Using a dull blade or bit and applying excessive force to compensate1st Year · Tools & Equipment#018 · Leaving tools on top of ladders or elevated surfaces where they can fall1st Year · Tools & Equipment#019 · Not returning borrowed tools to the tool crib or journeyman1st Year · Tools & Equipment#020 · Using the wrong drill bit material for the substrate (e.g., wood bit on metal)1st Year · Tools & Equipment#021 · Running the seam in the wrong direction, trapping water or allowing leakage1st Year · Sheet Metal Work#022 · Hammering a pittsburg seam without properly supporting the duct body1st Year · Sheet Metal Work#023 · Not aligning the drive cleats correctly before crimping, creating gaps1st Year · Sheet Metal Work#024 · Applying mastic sealant unevenly or missing interior joints entirely1st Year · Sheet Metal Work#025 · Forgetting to add allowance for the slip and drive connection when cutting duct1st Year · Sheet Metal Work#026 · Installing duct hangers too far apart, causing sagging between supports1st Year · Installation#027 · Not checking that duct is level before securing it permanently1st Year · Installation#028 · Over-tightening sheet metal screws and stripping them in 26-gauge material1st Year · Installation#029 · Failing to seal all duct joints with mastic or foil tape per code1st Year · Installation#030 · Installing a flex duct connection that is kinked at the elbow1st Year · Installation#031 · Installing supply and return ducts that are reversed at the air handler1st Year · Duct Systems#032 · Not protecting open duct ends from debris during construction1st Year · Duct Systems#033 · Forgetting to install turning vanes in a square duct elbow1st Year · Duct Systems#034 · Undersizing a branch takeoff because airflow CFM was not calculated1st Year · Duct Systems#035 · Not understanding the difference between a wye fitting and a tee fitting application1st Year · Duct Systems#036 · Showing up late repeatedly without communicating with the foreman1st Year · Coordination & Professionalism#037 · Not asking questions when unsure - guessing and installing something wrong1st Year · Coordination & Professionalism#038 · Failing to clean up your work area at the end of each shift1st Year · Coordination & Professionalism#039 · Leaving cut sheet metal scraps on the floor creating a slip and puncture hazard1st Year · Coordination & Professionalism#040 · Not reading the shop drawing before beginning fabrication1st Year · Coordination & Professionalism#041 · Not knowing the difference between supply air, return air, and outside air1st Year · Systems & Controls#042 · Confusing a VAV box with a fan coil unit on drawings1st Year · Systems & Controls#043 · Not understanding why static pressure matters in a duct system1st Year · Systems & Controls#044 · Installing a thermostat sensing element in direct sunlight or a draft1st Year · Systems & Controls#045 · Calling a diffuser a register and a register a grille (wrong terminology with the GC)1st Year · Systems & Controls#046 · Skipping a harness inspection before climbing a lift or scaffold2nd Year · Safety#047 · Not attending a required safety toolbox talk because it seems repetitive2nd Year · Safety#048 · Ignoring pinch-point hazards on mechanical equipment during installation2nd Year · Safety#049 · Not using hearing protection around running equipment during testing2nd Year · Safety#050 · Failing to call a line locator before cutting a ceiling that may have live conduit2nd Year · Safety#051 · Not verifying field dimensions before pre-fabricating a large duct run2nd Year · Measuring & Layout#052 · Laying out a duct transition using incorrect center-line math2nd Year · Measuring & Layout#053 · Forgetting to allow for duct insulation thickness when calculating clearances2nd Year · Measuring & Layout#054 · Not accounting for structure deflection when hanging duct near a beam2nd Year · Measuring & Layout#055 · Mis-transferring measurements from a tape to a shop drawing (transposing digits)2nd Year · Measuring & Layout#056 · Making a 45-degree offset without correctly calculating the setback distance2nd Year · Fabrication#057 · Fabricating a round-to-rectangular transition that is too abrupt, causing turbulence2nd Year · Fabrication#058 · Notching corners of a box incorrectly, leaving a gap that requires excessive caulking2nd Year · Fabrication#059 · Setting the pittsburg folder too deep and crushing the pocket2nd Year · Fabrication#060 · Building a fitting for the wrong gauge of metal (ordered 24 gauge, built for 26)2nd Year · Fabrication#061 · Not calibrating a digital angle finder before use on a critical layout2nd Year · Tools & Equipment#062 · Running a plasma cutter without checking consumables, ruining a large sheet2nd Year · Tools & Equipment#063 · Letting the bead roller drift off-line because feed pressure was uneven2nd Year · Tools & Equipment#064 · Using a grinder disc that is past its rated RPM for the grinder being used2nd Year · Tools & Equipment#065 · Not knowing how to set up a pipe threader for the correct die size2nd Year · Tools & Equipment#066 · Not properly forming a female end on duct so the joint won't pull apart2nd Year · Sheet Metal Work#067 · Cutting a round collar too large so it spins freely instead of gripping2nd Year · Sheet Metal Work#068 · Mis-rolling a spiral elbow segment so the seam is in the wrong position2nd Year · Sheet Metal Work#069 · Failing to double-hem raw edges on kitchen exhaust hoods for rigidity2nd Year · Sheet Metal Work#070 · Not pressing TDC (transverse duct connector) flanges down flush before assembly2nd Year · Sheet Metal Work#071 · Hanging duct from rebar or conduit not designed to carry the load2nd Year · Installation#072 · Installing a flexible connection without enough slack, transmitting vibration2nd Year · Installation#073 · Not coordinating with the plumber before installing duct that blocks a drain cleanout2nd Year · Installation#074 · Forgetting to install a fire damper in a rated wall penetration2nd Year · Installation#075 · Setting an air handler on isolator pads the wrong way, reducing isolation2nd Year · Installation#076 · Installing a straight run of duct without expansion joints in a long plenum2nd Year · Duct Systems#077 · Not lining duct that passes through an unconditioned space, losing thermal efficiency2nd Year · Duct Systems#078 · Connecting two different metal types (galvanized to stainless) without dielectric separation2nd Year · Duct Systems#079 · Forgetting that a spiral round duct system needs a proper end cap at dead ends2nd Year · Duct Systems#080 · Not sizing a flex duct collar to match the rigid duct diameter, causing flow restriction2nd Year · Duct Systems#081 · Failing to mark up as-built changes on the job drawings2nd Year · Coordination & Professionalism#082 · Not communicating a discovered conflict to the foreman before working around it2nd Year · Coordination & Professionalism#083 · Borrowing materials from another trade's stock without permission2nd Year · Coordination & Professionalism#084 · Signing off on work that you did not personally inspect2nd Year · Coordination & Professionalism#085 · Not attending pre-installation coordination meetings between trades2nd Year · Coordination & Professionalism#086 · Mixing up heating and cooling sequences when pre-wiring a unit2nd Year · Systems & Controls#087 · Not understanding the purpose of a bypass damper in a VAV system2nd Year · Systems & Controls#088 · Wiring a low-voltage thermostat at line voltage, destroying the thermostat2nd Year · Systems & Controls#089 · Not understanding the difference between 2-pipe and 4-pipe fan coil systems2nd Year · Systems & Controls#090 · Installing an economizer without verifying the damper opens in the correct direction2nd Year · Systems & Controls#091 · Not performing a proper pre-task hazard analysis before a non-routine task3rd Year · Safety#092 · Failing to barricade below an aerial lift work zone - no hard hat zone not enforced3rd Year · Safety#093 · Working in a confined space without a competent person sign-off and air monitor3rd Year · Safety#094 · Not reporting a near-miss incident because it seems minor3rd Year · Safety#095 · Skipping fall protection anchoring because the task feels quick3rd Year · Safety#096 · Not converting properly between fractions and decimals when using a precision rule3rd Year · Measuring & Layout#097 · Laying out a large duct bank without establishing a baseline control point first3rd Year · Measuring & Layout#098 · Using a laser level that is out of calibration and not verifying with a bubble level3rd Year · Measuring & Layout#099 · Not adjusting layout for building out-of-square conditions3rd Year · Measuring & Layout#100 · Incorrectly reading isometric drawings and building fittings that are handed wrong3rd Year · Measuring & Layout#101 · Not calculating metal stretch when laying out a tight-radius elbow3rd Year · Fabrication#102 · Building a double-wall duct liner panel that shifts during assembly3rd Year · Fabrication#103 · Welding galvanized steel without proper ventilation, releasing zinc fumes3rd Year · Fabrication#104 · Fabricating a duct section that exceeds the maximum unsupported length per SMACNA3rd Year · Fabrication#105 · Setting up a press brake for a complex profile without a test bend on scrap first3rd Year · Fabrication#106 · Not setting the correct air pressure for a pneumatic clincher before production runs3rd Year · Tools & Equipment#107 · Using a plasma table program that hasn't been proofed, wasting a full sheet3rd Year · Tools & Equipment#108 · Not cleaning the rolls on a slip roll machine, causing marks on finished duct3rd Year · Tools & Equipment#109 · Selecting the wrong interpolation on a CNC plasma for inside vs outside cuts3rd Year · Tools & Equipment#110 · Not verifying the square footage yield before nesting parts on a sheet3rd Year · Tools & Equipment#111 · Not installing a turning vane in the correct orientation relative to airflow direction3rd Year · Sheet Metal Work#112 · Crimping a collar on spiral duct before confirming the duct gauge is compatible3rd Year · Sheet Metal Work#113 · Applying insulation board to duct without staggering the seams3rd Year · Sheet Metal Work#114 · Fabricating kitchen exhaust grease duct without slope toward the grease trap3rd Year · Sheet Metal Work#115 · Installing a stainless grease duct without proper welded and tested seams3rd Year · Sheet Metal Work#116 · Not pre-planning the rigging sequence for a large air handler before the crane arrives3rd Year · Installation#117 · Installing vibration isolators upside down on a fan that has asymmetric loading3rd Year · Installation#118 · Hanging a coil section without checking drain pan tilt toward the drain connection3rd Year · Installation#119 · Not sealing kitchen exhaust duct penetrations through rated assemblies with intumescent3rd Year · Installation#120 · Routing duct through a structural bay without engineering approval for the opening3rd Year · Installation#121 · Overlooking the effects of duct leakage on system static pressure and fan selection3rd Year · Duct Systems#122 · Not completing a duct leakage test before concealing work in a ceiling3rd Year · Duct Systems#123 · Installing a sound attenuator (silencer) oriented backward relative to airflow3rd Year · Duct Systems#124 · Neglecting to balance takeoffs by adjusting splitter dampers during rough-in3rd Year · Duct Systems#125 · Not accounting for system effect losses at fan inlet when sizing ductwork3rd Year · Duct Systems#126 · Not coordinating with the fire protection contractor before installing duct near sprinklers3rd Year · Coordination & Professionalism#127 · Failing to flag a design error in the drawings - installing it wrong anyway3rd Year · Coordination & Professionalism#128 · Not issuing an RFI when a field condition contradicts the contract documents3rd Year · Coordination & Professionalism#129 · Failing to track materials used and report daily to the foreman for cost coding3rd Year · Coordination & Professionalism#130 · Not mentoring 1st and 2nd year apprentices working alongside you3rd Year · Coordination & Professionalism#131 · Misidentifying a chilled water coil valve as a heating valve and piping it wrong3rd Year · Systems & Controls#132 · Not understanding the sequence of operations for a heat recovery wheel3rd Year · Systems & Controls#133 · Confusing sensible heat and latent heat in a dehumidification application3rd Year · Systems & Controls#134 · Not verifying a VAV box actuator strokes fully open and closed before startup3rd Year · Systems & Controls#135 · Installing a mixed air plenum without leaving access for the mixing damper actuators3rd Year · Systems & Controls#136 · Accepting a jobsite condition that is unsafe rather than stopping work and escalating4th Year · Safety#137 · Not enforcing safety standards with apprentices under your supervision4th Year · Safety#138 · Becoming complacent about PPE because of years without an incident4th Year · Safety#139 · Underestimating the weight of a large duct assembly before rigging it overhead4th Year · Safety#140 · Not reviewing the MSDS/SDS sheet for a new sealant or flux being used on the job4th Year · Safety#141 · Failing to verify that shop drawings match the approved submittal before fabricating a full run4th Year · Measuring & Layout#142 · Not cross-checking duct elevations against the structural and plumbing BIM model4th Year · Measuring & Layout#143 · Laying out a complex mechanical room without a coordinated drawing set signed off by all trades4th Year · Measuring & Layout#144 · Cutting an entire prefab duct run to the wrong length because field dimensions were never verified4th Year · Measuring & Layout#145 · Not adjusting for seismic bracing clearances in a high seismic zone per SMACNA guidelines4th Year · Measuring & Layout#146 · Fabricating a replacement duct section without matching the original gauge and construction class4th Year · Fabrication#147 · Not verifying that shop-built fittings match the engineered pressure class for the system4th Year · Fabrication#148 · Producing flat oval duct that doesn't hold dimension after forming due to incorrect gauge selection4th Year · Fabrication#149 · Building a custom air handling cabinet without consulting the manufacturer's structural requirements4th Year · Fabrication#150 · Not pressure-testing a custom grease duct assembly before installation per NFPA 964th Year · Fabrication#151 · Not maintaining the shop's plasma table cutting head consumables on a defined schedule4th Year · Tools & Equipment#152 · Allowing apprentices to use equipment without verifying they have been trained and authorized4th Year · Tools & Equipment#153 · Not calibrating measuring tools (squares, protractors) at the start of a precision project4th Year · Tools & Equipment#154 · Failing to report a malfunctioning brake press rather than working around it4th Year · Tools & Equipment#155 · Using rigging equipment that has not been inspected within the required time period4th Year · Tools & Equipment#156 · Approving a duct joint for concealment that has visible gaps or missing sealant4th Year · Sheet Metal Work#157 · Not specifying the correct duct construction class to the shop when ordering prefab sections4th Year · Sheet Metal Work#158 · Installing exposed architectural ductwork without protecting finished surfaces during rigging4th Year · Sheet Metal Work#159 · Not field-verifying that pre-punched TDC duct flanges align before ordering an entire duct package4th Year · Sheet Metal Work#160 · Signing off on insulated duct that has vapor barrier damage allowing condensation into the liner4th Year · Sheet Metal Work#161 · Not establishing a proper rigging plan reviewed by a foreman before setting a large RTU4th Year · Installation#162 · Forgetting to install access doors at every fire damper, control valve, and coil in the system4th Year · Installation#163 · Not confirming that duct seismic bracing is installed per the structural engineer's stamped details4th Year · Installation#164 · Allowing duct to be installed that will block code-required clearances for electrical panels4th Year · Installation#165 · Not verifying that a rooftop unit curb is level and flashed before setting the unit4th Year · Installation#166 · Overlooking external static pressure when selecting a replacement fan for a retrofit4th Year · Duct Systems#167 · Not accounting for diversity factor when sizing a multi-zone VAV supply duct main4th Year · Duct Systems#168 · Designing a duct path that creates excessive system effect at the fan discharge4th Year · Duct Systems#169 · Ignoring duct leakage class requirements on a high-pressure system above 3 inches WG4th Year · Duct Systems#170 · Not coordinating supply air outlet placement to avoid short-circuiting with return air intakes4th Year · Duct Systems#171 · Failing to submit project closeout documents - O&M; manuals, warranties, as-builts - on time4th Year · Coordination & Professionalism#172 · Not preparing a written punch list walk with the GC before final inspection4th Year · Coordination & Professionalism#173 · Letting scope creep happen without notifying the PM for a potential change order4th Year · Coordination & Professionalism#174 · Not documenting verbal owner requests in writing before performing extra work4th Year · Coordination & Professionalism#175 · Failing to communicate a schedule slippage to the GC before it impacts other trades4th Year · Coordination & Professionalism#176 · Not performing a full air balance before the owner's TAB contractor arrives, wasting their time4th Year · Systems & Controls#177 · Signing off on controls work that has not been commissioned through a full sequence test4th Year · Systems & Controls#178 · Not verifying that BAS points are mapped correctly before owner training4th Year · Systems & Controls#179 · Failing to confirm refrigerant charge is correct before accepting a startup on a new split system4th Year · Systems & Controls#180 · Not providing the owner with filter change schedules and maintenance access instructions at turnover4th Year · Systems & Controls