2.4 IDLH atmospheres and the arrangements around them
IDLH is the point where respiratory protection stops being about filters and starts being about rescue. The standard gives you two acceptable devices, and then surrounds them with a set of arrangements — standby personnel, communication, retrieval equipment — that exist because the assumption is that something will go wrong and somebody will have to come and get you.
1 The definition, and the three ways in
Paragraph (b): immediately dangerous to life or health (IDLH) means an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere.
Three separate ways an atmosphere qualifies, and only the first matches most people's intuition. The second covers exposures whose damage is permanent even if the worker walks out. The third covers anything that makes self-rescue impossible — narcosis, disorientation, loss of coordination — regardless of how toxic the substance is over a shift.
Two further rules bring atmospheres into the category without any measurement at all. Paragraph (d)(1)(iii): where the employer cannot identify or reasonably estimate the employee exposure, the atmosphere shall be considered IDLH. Paragraph (d)(2)(iii): all oxygen-deficient atmospheres shall be considered IDLH, subject only to the narrow Table II altitude exception, which permits any atmosphere-supplying respirator — still not an air-purifying one.
2 The only two acceptable respirators
Paragraph (d)(2)(i) is a closed list. For employee use in IDLH atmospheres the employer shall provide:
- 1(A) A full facepiece pressure demand SCBA certified by NIOSH for a minimum service life of thirty minutes; or
- 2(B) A combination full facepiece pressure demand supplied-air respirator with auxiliary self-contained air supply.
Notice what both have in common: full facepiece, pressure demand, and an independent air supply that does not depend on the atmosphere. Notice also what the second one carries — an auxiliary self-contained supply, so that a severed or blocked airline does not leave the wearer with nothing.
Escape-only devices are handled separately at (d)(2)(ii): respirators provided only for escape from IDLH atmospheres shall be NIOSH-certified for escape from the atmosphere in which they will be used. And Note 5 to Table 1 confirms that the assigned protection factors in that table do not apply to respirators used solely for escape.
3 The arrangements around the entry
Paragraph (g)(3) sets out what must be in place for all IDLH atmospheres. It is a rescue architecture, and every item assumes the person inside will not be able to help themselves.
| ¶ | Requirement |
|---|---|
| (g)(3)(i) | One employee or, when needed, more than one employee is located outside the IDLH atmosphere |
| (g)(3)(ii) | Visual, voice or signal line communication is maintained between those inside and those outside |
| (g)(3)(iii) | The employees outside are trained and equipped to provide effective emergency rescue |
| (g)(3)(iv) | The employer or designee is notified before the outside employees enter to provide rescue |
| (g)(3)(v) | Once notified, the employer or designee provides necessary assistance appropriate to the situation |
| (g)(3)(vi)(A) | The outside employees are equipped with pressure demand or other positive pressure SCBA, or a pressure demand supplied-air respirator with auxiliary SCBA |
| (g)(3)(vi)(B)-(C) | And with appropriate retrieval equipment where it would contribute to rescue without increasing overall risk, or equivalent means for rescue where retrieval equipment is not required |
Two of those are frequently skipped in practice. The standby person must be equipped, not merely present — someone standing outside in a hard hat is not what (g)(3)(vi)(A) describes. And the notification at (g)(3)(iv) has to happen before the rescuer enters, which means there is a plan and a phone, not an improvisation.
4 Interior structural firefighting
Paragraph (g)(4) adds three requirements on top of (g)(3) for interior structural fires: at least two employees enter the IDLH atmosphere and remain in visual or voice contact with one another at all times; at least two employees are located outside; and all employees engaged in interior structural firefighting use SCBAs.
That is the origin of the arrangement most people know as two-in, two-out. Note 1 to paragraph (g) adds a practical allowance: one of the two individuals located outside may be assigned an additional role, such as incident commander or safety officer, so long as that individual is able to perform assistance or rescue activities without jeopardizing the safety or health of any firefighter working at the incident.
Paragraph (b) defines interior structural firefighting as the physical activity of fire suppression, rescue or both, inside of buildings or enclosed structures which are involved in a fire situation beyond the incipient stage. The words “beyond the incipient stage” matter: an incipient-stage fire attacked with a portable extinguisher is a different situation, governed by 1910.157.
5 Where IDLH work meets other standards
An IDLH atmosphere almost never arrives alone. Three other standards usually apply at the same time, and their requirements are cumulative, not alternative.
29 CFR 1910.146, permit-required confined spaces. An oxygen-deficient or otherwise hazardous atmosphere inside a permit space brings the entire permit system: entry permit, attendant, entry supervisor, atmospheric testing before and during entry, and rescue arrangements. The (g)(3) standby person and the 1910.146 attendant are related ideas with separate rule sets.
29 CFR 1910.120(q), emergency response. Paragraph (q)(3)(iv) requires employees engaged in emergency response and exposed to an inhalation hazard or potential inhalation hazard to wear positive pressure SCBA until the individual in charge of the incident command system determines through the use of air monitoring that a decreased level of respiratory protection will not result in hazardous exposures. Positive pressure SCBA is the default, and monitoring is what allows stepping down.
29 CFR 1910.147, lockout/tagout, wherever the reason for the atmosphere is a process that has to be isolated before anyone goes in.
6 The honest question before an IDLH entry
Everything in this chapter is expensive: SCBA, trained standby personnel, retrieval equipment, a notified employer, a communication method that survives. That expense is the point. The arrangements are costly because the situation is one where a mistake is unrecoverable, and building them is the standard's way of forcing the question that ought to come first.
Can the atmosphere be eliminated instead? Ventilated, purged, isolated, drained, or the task done from outside? Paragraph (a)(1) asked that question at the very start of the standard, and it is never more worth asking than here. Most IDLH entries that go wrong were entries that did not have to happen.
If the answer is genuinely no, then the two devices at (d)(2)(i), the arrangements at (g)(3) and — where a permit space is involved — the whole of 1910.146 are the minimum. There is no partial version.
- IDLH includes atmospheres that merely impair the ability to escape, not only ones that kill quickly.
- Unknown atmospheres and all oxygen-deficient atmospheres are considered IDLH.
- Only a full facepiece pressure demand SCBA with a 30-minute minimum service life, or a pressure demand SAR with auxiliary SCBA, is acceptable.
- Maximum use concentrations are never applied to IDLH conditions.
- (g)(3) requires standby personnel who are outside, in contact, trained and equipped for rescue, with notification before they enter.
- Interior structural firefighting adds two-in, two-out and SCBA for everyone inside.
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