Most fire extinguishers today are stored pressure dry chemical extinguishers, meaning the dry chemical extinguishing agent is stored in the same cylinder as the expellant gas. This type of extinguisher is designed so that almost anyone can discharge the contents by pulling the pin and squeezing the lever. Although straight forward in design, the extinguisher cylinder requires special attention during annual maintenance to ensure it’s ready to operate.
Trained extinguisher technicians perform planned preventative maintenance on a regular schedule to enhance the safety and reliability of cylinders. The external and internal maintenance examinations are intended to give maximum assurance that the extinguisher will operate safely and to determine if physical damage or other conditions exists that would affect safety.
Any extinguisher that has obvious damage (including dents or corrosion) that is significant enough to cause weakness to the cylinder, must be hydrostatically tested.
If the damage is significant, the cylinder is condemned, under any of the following conditions:
- The cylinder has been used for a purpose other than as a fire extinguisher
- Repairs are observed, including soldering, welding, brazing, or patching compounds
- Threads are corroded, crossthreaded, broken, or nicked
- Internal cylinder walls show signs of corrosive pitting
- There is corrosive pitting under the nameplate
- The cylinder has been exposed to a fire or similar excessive heat
- If not on a weld, a dent that exceeds 1 ⁄10 of the greatest dimension of the dent
- A dent that exceeds 1 ⁄4” (6 mm) if a dent includes a weld
- Any corrosion, cuts, gouges, or dings where 10% of the minimum wall thickness is removed.
It is extremely important to perform periodic external and internal cylinder examinations to identify physical damage before it becomes a safety issue. Knowing examination frequencies, what to look for, and having the special tools needed to do the job right will provide maximum assurance that dry chemical extinguishers are safe and ready to use in the event of a fire emergency.