page_title: Chainsaw safety features
section_title: Chain brake
hierarchical_section_title: Chainsaw safety features / Chain brake
context_page_description: Chainsaws incorporate numerous safety features common to many engine-driven power tools. Manufacturers have invented numerous design features to improve safety. Some features have become de facto standards, and others are legal requirements in particular jurisdictions. Best practice dictates that an operator should inspect the saw before starting work and only operate the saw if all the safety features are properly functional.
  Additional safety features are a significant commercial advantage to chainsaw producers. Companies continue to develop new features over time. Most chainsaw safety features are focused on the kickback problem, and seek to either avoid it, or to reduce the risk of injury should it occur.
  In addition to the safety features built into the chainsaw, operators should also wear specific chainsaw safety clothing. Most older saws have few or none of these features, and extra care should be taken in their use.
context_section_description: Chain brakes prevent movement of the saw's cutting chain by applying a steel brake band around the driven clutch drum. Clamping force for the brake band is provided by a powerful spring. The chain brake has two purposes. First, it can be used to secure the chain when changing position, moving between cuts or starting a cold saw, which requires a partly open throttle. This would otherwise lead to uncontrolled chain movement, a major hazard in older saws. Secondly, the chainbrake can activate under kickback conditions to prevent the operator from being struck by a running chain. Being struck by even a static chain may cause serious injury, but anything that can be done to mitigate the usually dreadful injuries caused by contact with a moving chain is of considerable benefit to operators. Kickback injuries usually occur to the head, face, neck and shoulders; when a running chain is involved, such injuries are usually very serious, often disfiguring and sometimes fatal.
  The chain brake is principally operated by the top-hand guard being pushed forward to engage the brake, and pulled back to disengage. The spring-loaded action allows powerful braking under emergency conditions and can halt a chain under full power in a fraction of a second. Correspondingly, it may require considerable force to reset.
  The chain brake may be activated deliberately by the operator, or automatically by the force of a kickback event. In the former, the operator usually rotates his left wrist and knocks the top hand guard forward with the back of his hand, re-setting it by reaching forward with his fingers to pull the top hand guard backwards. In the case of a kickback event the operator's left hand may be violently dislodged from the handle and the top hand guard will be thrown onto his hand, forcing activation of the chainbrake. Husqvarna models also incorporate a link between the top handle and the chain brake trigger, applying the brake if the saw's bar is forced suddenly upwards. This is known as an "inertia" chainbrake and will allow activation of the chainbrake even if the operator's left hand is not removed from the handle.
  The chain brake may also be of use when sharpening a chain on a bar, as it allows robust filing to take place without the chain slipping about. 
  "Wrap-around" top-hand guards restrict movement and make no allowance for the fact that when the handle is gripped on the lower section of the handle (left side of the saw from the operator's viewpoint) it is usually for making lateral, right-to-left cuts. In this situation the operator's head, neck and shoulders are out of the cutting plane of the saw and will generally not be struck even if a kickback does occur.
caption: Front handguard, and combined chain brake lever
exif: {"Image Make": "FUJIFILM", "Image Model": "FinePixS2Pro", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS Windows", "Image DateTime": "2005:06:22 10:27:43", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "", "Image ExifOffset": "236", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "934", "Thumbnail JPEGInterchangeFormatLength": "4852", "EXIF ExposureTime": "1/20", "EXIF FNumber": "8", "EXIF ExposureProgram": "Aperture Priority", "EXIF ISOSpeedRatings": "200", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2005:06:22 10:05:11", "EXIF DateTimeDigitized": "2005:06:22 10:05:11", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "2", "EXIF ShutterSpeedValue": "9/2", "EXIF ApertureValue": "6", "EXIF BrightnessValue": "9/2", "EXIF ExposureBiasValue": "0", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Shade", "EXIF Flash": "Flash did not fire", "EXIF FocalLength": "105", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1440", "EXIF ExifImageLength": "960", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "808", "EXIF FocalPlaneXResolution": "630", "EXIF FocalPlaneYResolution": "630", "EXIF FocalPlaneResolutionUnit": "3", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Manual", "EXIF FocalLengthIn35mmFilm": "157", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Hard", "EXIF Saturation": "Normal", "EXIF Sharpness": "Soft", "EXIF SubjectDistanceRange": "0"}