Recently, it was discovered (see photo 1)
that a perchloric acid fume hood was heavily contaminated with potentially explosive
perchloric acid salts (see photo 2). Due to a malfunction in
the was-down system only the interior of the hood was subjected to a water spray. The duct
from the top of the hood to the stack on the roof had not been washed down for an
undetermined length of time while perchloric acid continued to be heated in the hood (see photo 3). As a result, perchloric acid salts formed on many
locations along the length of the duct, particularly where the stainless steel welds were
made (see photo 4). Although only visible on the outside, it
is presumed contamination is worse on the interior of the stainless duct (see photo 5). Of particular concern is the wood floor in the
attic (see photo 6). Wood (and other organic materials) that
have been contaminated with perchloric acid can become flammable and/ or explosive with
heat or friction. As a result of the non-functional wash-down system (see photo 7) the fan located on the roof was completely
destroyed by the acid (see photo 8). To prevent this type of
situation, follow these steps when working with perchloric acid:
1. Always wear goggles and rubber gloves when pouring or handling perchloric acid.
2. Working with solutions of 70% or more requires a face shield, apron and special
handling procedures identified in the CRC excerpt below.
3. Clean up spills immediately.
4. A preventive maintenance program must be in effect for perchloric acid hoods and
other hoods where hazardous materials are used.
5. Never heat perchloric acid in a chemical hood unless the hood has been designed for
use with perchloric acid and has a functioning wash-down system.
6. Flush the system for at least 20-30 minutes at the end of each work session.
7. Always store acids separately from organic solvents.
8. Consider performing testing to determine if perchloric acid or perchlorates
are building up on surfaces:
Perchloric Acid Sampling and
Analysis Procedure, Brookhaven National Laboratory, Safety and Health Services
Division. This document describes a field procedure for taking and analyzing
wipe samples from surfaces potentially contaminated with perchlorates and perchloric acid.
The following excerpts contain additional safety precautions that should be followed
and describe actual perchloric acid accidents that have occurred.
Excerpt from
CRC Handbook of Laboratory Safety. 4th Edition, 1995 by CRC Press LLC,
Excerpt from NFPA 45,
Standard on Fire Protection for Laboratories using Chemicals.
