Allegro 9533-25 Confined Space Blower (831 CFM + 25 ft Duct) Review

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Allegro's 9533-25 is the standard-issue confined space ventilation package: an 831 CFM axial blower with 25 feet of duct in the box, sized for the manholes and vaults that make up most permit entries.

Editorial rating: 4.5/5. The sensible default. And the non-negotiable footnote: ventilate, then verify with a gas monitor — airflow never clears a space by itself.

Key specs

Listed at $319.95 on Amazon when we captured pricing (2026-07-11) — the button shows the live price.

Who it's for

Any crew doing pre-entry purges and continuous ventilation on typical municipal/industrial entries — this is the default first blower.

Skip it if

Large vaults and long duct runs; when volume is big or the duct path is ugly, step up to a 3,000 CFM class unit.

How it fits a permit-required entry system

Ventilation runs before and during every entry, but the entry decision belongs to the gas monitor. Purge, ventilate continuously, test, and only then enter. New to the category? Start with the confined space equipment collection overview, which walks the winch-vs-SRL decision and ventilation sizing.

How it compares

vs MOUNTO 3,000 CFM: volume for big spaces, duct sold separately. (Our take: full MOUNTO 3,000 CFM review.)

vs TRSMIMA kit: if the same budget must also cover retrieval. (Our take: full TRSMIMA kit review.)

Pros and cons

Pros

• Duct included — works day one
• 831 CFM suits standard manholes
• Allegro is the known name in entry ventilation

Cons

• Undersized for large vaults
• 1/3 hp motor caps duct-run length
• Duct storage adds bulk to the truck

Build out the rest of the entry program

Retrieval hardware is one leg of a permit program. Test atmospheres with a 4-gas monitor (see the H2S monitor guide and industrial CO monitors), fit every entrant with a full-body harness from the harness collection, isolate energy with lockout/tagout, and stage a trauma kit at the opening. Where atmospheres can't be cleared, step up to supplied-air respirators or a PAPR system. Rules and rationale: when fall protection is required, OSHA ladder requirements, and assigned protection factors. Browse everything in the confined space equipment collection or the wider fall protection range, including self-retracting lifelines and fall protection kits.

Related confined space reviews

Start with the ranked best confined space tripod kits guide for the full 12-system comparison.

• TRSMIMA Confined Space Tripod Kit (1200 lb) review
• VEVOR Confined Space Tripod Kit (1800 lb) review
• VEVOR Confined Space Tripod Kit (2600 lb) review
• MSA 10102002 Workman Tripod (8 ft) review
• 3M DBI-SALA 8000140 Confined Space Aluminum Tripod review
• 3M DBI-SALA 8000141 Confined Space Aluminum Tripod (Tall) review
• FallTech 7507 Confined Space Tripod Kit review

Confined space equipment FAQ

Do I need this equipment for every confined space entry?

Permit-required confined spaces under OSHA 29 CFR 1910.146 need a retrieval system unless it would increase risk or wouldn't help rescue, and vertical entries deeper than 5 feet require a mechanical retrieval device. Non-permit spaces still deserve ventilation and testing — classification comes first.

What's the difference between a winch and a 3-way retrieval SRL?

A winch raises and lowers under control but doesn't arrest falls. A 3-way SRL arrests a fall instantly and then cranks over into retrieval mode. Rescue-ready systems typically run both: the entrant on the SRL, the winch as the working line.

Are import-brand kits (VEVOR, TRSMIMA) OK for permit entries?

OSHA sets performance requirements rather than certifying products. Certified brands publish ANSI Z359-family test documentation; import listings state capacities but documentation varies. Verify what your written program requires before standardizing on them.

What else does a compliant entry need besides retrieval hardware?

Atmospheric testing with a calibrated 4-gas monitor, continuous ventilation, an attendant, communication, a written rescue plan, lockout/tagout on connected energy, and trained entrants. Hardware supports the program — it doesn't replace it.

Does ventilation make a space safe to enter?

No. Ventilation reduces contaminant levels; the entry decision rests on gas-monitor readings taken after ventilating. If readings stay outside limits, the answer is supplied-air respiratory protection and a revised plan, not more airflow.

How do I size cable length for my entries?

Match line length to your deepest entry with margin, and check winch cable and SRL working length separately when a kit includes both — they're rarely identical.

Can the personnel winch lift tools and materials?

Keep a dedicated material line. The man-rated winch stays rigged for the entrant; hauling gear on it risks dropped objects and takes your rescue line out of service.

How often does this equipment need inspection?

Before each use by the user, plus formal periodic inspection per the manufacturer's schedule (commonly at least annually by a competent person). SRLs additionally follow the maker's recertification requirements.

What harness works with these systems?

A full-body harness with a dorsal D-ring for SRL fall arrest; many programs also spec shoulder D-rings for vertical winch retrieval. Fit matters more than brand — see our harness buyer's guide for sizing.

Who is allowed to perform confined space rescue?

Your written plan decides: non-entry retrieval by the attendant using this hardware is the first answer. Entry rescue requires a trained, equipped rescue team — never an improvised grab by coworkers, which is how multiple-fatality incidents happen.

Do these products come with affiliate pricing markup?

No — the Amazon buttons link to the same public listing anyone sees. WC Safety earns a commission from Amazon at no extra cost to you, which funds this testing-free, spec-honest review format.

Where do gas monitors fit into the budget?

Before everything else. If the budget forces sequencing, a calibrated 4-gas monitor precedes retrieval hardware, because testing determines whether entry is permissible at all.

How many air changes does a pre-entry purge need?

A common practice is 7+ air changes before entry, then continuous ventilation during occupancy — but your program's numbers govern. Calculate from space volume ÷ blower CFM, derated for duct losses.

Does duct length change performance?

Substantially — every foot and every bend costs airflow. Keep runs short and straight, and size up the blower when the path is ugly.

Should the blower run during the whole entry?

Yes, continuous ventilation during occupancy is standard practice, with the gas monitor logging throughout — ventilation and monitoring work together, never as substitutes.

How we review

WC Safety reviews are spec-honest: we work from the manufacturer's published data and the live Amazon listing, flag any claim that exists only in listing copy ("per the listing"), and never invent certifications or test results. Where certified-brand documentation (ANSI Z359 family) exists we say so; where it doesn't, we say that too.

Sources

OSHA 29 CFR 1910.146 (permit-required confined spaces); manufacturer product pages and the Amazon listing linked above; ANSI/ASSP Z359 fall-protection standard family (referenced, not reproduced).

Reviewed by Steven Eaton, WC Safety — workplace PPE retailer and Amazon Associate. Pricing captured 2026-07-11; click through for current pricing.